and the size of the riser should be made equal to the size of the
horizontal branch thereto throughout its length, wherever this branch
is not larger than 2¹⁄₂ in. diameter. When larger, reductions in the
riser can be made until 2¹⁄₂ in. is reached when this size should be
maintained throughout the remainder of its length. No riser should be
made less than 2¹⁄₂ in. unless a lift is necessary.
Before finally fixing the size of riser to be used in any case the
size of the branch in the horizontal lines serving the same must be
approximately determined.
These sizes will be dependent on the location in which it is necessary
to install the vacuum producer. In the case of the building (Fig. 61)
the most desirable location for the vacuum producer will be in the
exact center of the building.
With the vacuum producer centrally located the longest run from any
riser will be 55 ft. To this we must add:
5 ft. for each long-turn elbow.
10 ft. for each short-turn elbow.
10 ft. for entrance to each long sweep Y branch.
20 ft. for entrance to a tee branch, except at sweeper inlets on
risers, where 10 ft. is ample.
In calculating the riser friction for risers under 150 ft. in length
the whole capacity of the riser can be assumed as being connected to a
point midway of its length.
In the eight-story building (Fig. 61) the length of the riser from
basement ceiling to eighth floor will be 100 ft. and the length to
be figured, 50 ft. The equivalent length of pipe line for any of the
risers, with the vacuum producer centrally located, will be:
From entrance tee into riser 10 ft.
Length of riser, one-half total length 50 ft.
Turn at base of riser 10 ft.
Run in basement 55 ft.
Y branch or elbow 10 ft.
Elbow at separator 5 ft.
------
Equivalent length 140 ft.
Each riser is to serve two sweepers and must pass 140 cu. ft. of free
air per minute. This will give a friction loss in a 2¹⁄₂-in. pipe of 2
in. mercury, if 10 in. mercury be maintained at the hose cock and 1-in.
hose used; and 1.5 in. mercury if 6 in. mercury be maintained at the
hose cock and 1¹⁄₄-in. hose used. Either of these figures are within
the limits set for the maximum friction loss and 2¹⁄₂-in. pipe will be
the proper size for the risers and their branches in the basement.
The portion of the main in the basement that serves the two risers on
either side of the building (portion “ab,” Fig. 61) must be of such
size as will produce the same loss in vacuum with 280 cu. ft. of air
passing as the 2¹⁄₂-in. pipe gives with 140 cu. ft. of air passing.
This may be determined from any table of equalization of pipes or may
be obtained from the chart, Fig. 48, in the following manner:
Find the intersection of the horizontal line “140” with the diagonal
representing a 2¹⁄₂-in. pipe and pass on the nearest vertical to its
intersection with the horizontal line “280.” The diagonal inclined
toward the left passing nearest this intersection will be the pipe
size required. In this case a 3-in. pipe will give a slightly greater
friction and will be sufficient.
Unfortunately, it is rarely possible to locate the vacuum producer
in as favorable a point as that given in the illustration, but an
effort should always be made to select a location as nearly central to
all risers as possible. The basements of modern office buildings are
generally crowded and the space assigned to the mechanical equipment is
limited and owing to the necessity of ventilation, the vacuum producer
is generally located near the outside of the building.
Probably the best location that could be obtained in this case would be
at “d” (Fig. 62). The length of piping to risers 1 and 2 would now be
the same as that to all risers in case of Fig. 61, but the distance to
risers 3 and 4 will be increased 50 ft. It will be possible to increase
the size of the pipe line “bd” to the maximum size to serve four
sweepers, or 3¹⁄₂ in., the risers and their branches to remain 2¹⁄₂ in.
The total friction loss to risers 1 and 2 will now be:
Entrance to tee in risers, 10 ft. plus 50 ft. 60 ft.
Turn at base of riser, 10 ft., branch from “c” to riser 32 ft. 42 ft.
Entrance to tee in main 20 ft.
-------
Total equivalent length of 2¹⁄₂-in. pipe 122 ft.
When 1-in. hose is used the density of the air entering the 2¹⁄₂-in.
pipe is equivalent to a vacuum of 10 in. mercury and the friction loss
in the 2¹⁄₂-in. pipe will be 1.9 in. mercury. When 1¹⁄₄-in. hose is
used, the density of the air entering the pipe will be equivalent to a
vacuum of 6-in. mercury and the friction loss in the 2¹⁄₂-in. pipe will
be 1.32 in. mercury.
[Illustration: FIG. 62. ELEVATION OF LAYOUT FOR OFFICE BUILDING,
SHOWING BEST LOCATION (AT D) FOR VACUUM PRODUCER.]
The density of the air entering the 3¹⁄₂-in. pipe, “bd,” will be
equivalent to a vacuum of 11.9 in. mercury when 1-in. hose is used,
and to 7.32 in. mercury when 1¹⁄₄-in. hose is used. The friction loss
in the 3¹⁄₂-in. pipe will be 0.31 and 0.23 in. mercury, respectively.
Total friction loss to inlets on risers 1 and 2 will be 2.21 in. with
1-in. hose in use, and 1.55 in. with 1¹⁄₄-in. hose.
To obtain the friction loss to inlets on risers 3 and 4 the friction
loss in the pipe “bc” must be added to the above figures. With 50 ft.
of 3¹⁄₂-in. pipe carrying 280 cu. ft. free air the friction loss is 0.6
in. when the vacuum in the pipe is 12 in. and 0.4 when the vacuum in
the pipe is 8 in.
The total loss of vacuum to inlets on risers 3 and 4 will be 2.91 in.
if 1-in. hose is used and 1.95 in. if 1¹⁄₄-in. hose is used. In this
case, the total loss from inlet to vacuum producer is approximately
equal to the maximum variation of vacuum permitted at sweeper outlets
when 1¹⁄₄-in. hose is used, but is greater than when 1-in. hose is used.
However, it is the variation in vacuum at the hose cock farthest
from and that nearest to the vacuum producer that fixes the maximum
variation allowable. In this case it will be the difference in vacuum
between an inlet on riser 1 or 2 and a similar inlet on riser 3 or
4. The difference in vacuum at the bases of these risers will be the
friction loss in the pipe “bc,” and the total difference in friction in
the risers will occur when one sweeper is attached to the lowest inlet
on one riser, and one sweeper on the eighth and one on the seventh
floor on the other riser. The friction loss in the riser having the two
sweepers attached to its upper inlets will be:
15 ft. of 2¹⁄₂-in. pipe from seventh to eighth floors, 70 cu. ft. of
free air per minute, or 0.051 in. with a density equivalent to 6-in.
vacuum, and 0.075 in. with a density equivalent to 10-in. vacuum.
85 ft. of 2¹⁄₂-in. pipe from first to seventh floors, 140 cu. ft. free
air per minute, or 0.25 in. with a density equivalent to 6-in. vacuum,
and 0.42 in. with a density equivalent to 10-in. vacuum.
The total difference in vacuum at the hose cocks will be:
0.051 + 0.25 + 0.4 = 0.7 in. with 6-in. vacuum at the hose cock.
0.075 + 0.42 + 0.6 = 1.15 in. with 10-in. vacuum at the hose cock.
Either of these values are well within the maximum variation. It is,
therefore, evident that when the vacuum producer cannot be centrally
located that a piping system which will give the most nearly equal
length of pipe to each riser will yield the best results.
A vacuum cleaning system for serving a passenger car storage yard will
best illustrate the effect of long lines of piping. A typical yard
having 8 tracks, each of sufficient length to accommodate 10 cars, is
shown in Fig. 63. The vacuum producer in this case is located at the
side of the yard at one end, which is not an unusual condition.
[Illustration: FIG. 63. VACUUM CLEANING LAYOUT FOR A PASSENGER CAR
STORAGE YARD.]
The capacity of this yard will be 80 cars which must generally be
cleaned between the hours of midnight and 6 A. M., or a period of 6
hours for cleaning.
It will require one operator approximately 20 minutes to thoroughly
clean the floor of one car, on account of the difficulty in getting
under and around the seat legs. In addition to this, it is also
necessary to clean the upholstery of the seats and their backs, which
will require approximately 25 minutes more or 45 minutes for one
operator to thoroughly clean one car. Therefore, one operator can clean
8 cars during the cleaning period and a ten-sweeper plant will be
necessary to serve the yard.
One lateral cleaning pipe must be run between every pair of tracks or
four laterals in all to properly reach all cars without running the
hose across tracks where it might be cut in two by the shifting of
trains.
Outlets should be spaced two car lengths apart in order to bring an
outlet opposite the end of every second car. This will make it possible
to bring the hose in through the end of the car at the door opening and
clean the entire car from one end which can be done by using 100 ft. of
hose. The use of double the number of outlets and 50 ft. of hose would
require two attachments of the hose to clean one car resulting in a
loss of time in cleaning and is not recommended.
In this case, 100 ft. of hose would be the shortest length that would
be likely to be used and 60 cu. ft. of free air would be the maximum to
be allowed for when using 1¹⁄₄-in. hose.
The simplest layout for a piping system to serve this yard would be
that shown in Fig. 63.
When the entire yard is filled with cars and the entire force of ten
operators is started to clean them it would be possible to so divide
them that not over three operators would be working on any one lateral
and this condition will be assumed to exist. The maximum size for the
laterals between the tracks will be that for three sweepers, or 3 in.,
and it will not be safe to use this size beyond the second inlet from
the manifold, from which point to the end of the lateral it must be
made 2¹⁄₂ in., the maximum size for either one or two sweepers. The
total loss of pressure due to friction from the inlet at x (Fig. 63)
to the separator can be readily calculated from the chart (Fig. 56) as
follows:
TABLE 20.
PRESSURE LOSSES FROM INLET TO SEPARATOR IN SYSTEM FOR CLEANING RAILROAD
CARS.
--------+---------+----------+---------+--------+--------+--------
| | | |Average |Friction| Final
|Cubic Ft.|Equivalent| Size of | Vacuum,| Loss, |Vacuum,
Section | Free Air| Length, | Pipe, | Ins. | Ins. | Ins.
of Pipe.| per min.| feet. |In. Diam.|Mercury.|Mercury.|Mercury.
--------+---------+----------+---------+--------+--------+--------
x--5 | 60 | 150 | 2¹⁄₂ | 6 | 0.35 | 6.35
5--4 | 120 | 140 | 2¹⁄₂ | 7 | 1.35 | 7.70
4--2 | 180 | 280 | 2¹⁄₂ | 11 | 7.0 | 14.70
2--w | 180 | 190 | 3 | 16 | 4.0 | 18.70
w--u | 360 | 20 | 5 | 19 | 0.9 | 19.60
u--s | 480 | 20 | 6 | 20 | 0.5 | 20.10
s--sep | 600 | 20 | 6 | 20 | 0.4 | 20.50
--------+---------+----------+---------+--------+--------+--------
This loss will be the maximum that is possible under any condition as
it is computed with three sweepers working on the three most remote
inlets on laterals “xy” and “vw” and with two sweepers on laterals
“tu” and “rs.” The pipes are the largest which will give a velocity
of 40 ft. per second with the full load and at the density which
will actually exist in the pipe lines with the vacuum maintained at
the separator of 20 in. mercury in all cases, except the pipe from
“s” to separator. There the size was maintained at 6 in., as it was
not considered advisable to increase this on account of the reduced
velocity which would occur when less than the total number of sweepers
might be working.
As bare floor brushes will be used for cleaning coaches it is not
considered advisable to reduce the air quantity below that required by
such renovators. However, when carpet renovators are used in Pullman
cars and upholstery renovators are used on the cushions of both coaches
and Pullmans, the air quantity will be reduced. This condition may
exist at any time, also one of these carpet or upholstery renovators
may be in use on one of the inlets most remote from the separator at
the same time that nine floor brushes are in use on the remaining
outlets. In that case a vacuum at the separator of less than 20 in.
would result in a decrease in the vacuum at the inlet to which this
renovator was attached. The vacuum at the separator must, therefore, be
maintained at the point stated.
With such a vacuum there will be variation in the vacuum at the hose
cocks of from 6 in. to 20 in. or seven times the maximum allowable
variation in vacuum at the hose cocks.
If 1-in. hose be used, the maximum air quantities will be 40 cu. ft.
per sweeper. If we start with a vacuum at the inlet “x” of 10-in.
mercury, the vacuum at the separator will again be 20 in. and we now
have a variation of 10 in. between the nearest and most remote inlet
from the separator, or five times the maximum allowed.
Either of these conditions is practically prohibitive, due to:
1. The excessive power consumption at the separator. 50 H. P. in case
1¹⁄₄-in. hose is used, and 33 H. P. in case 1-in. hose is used.
2. The excessive capacity of the exhauster in order to handle the air
at such low density, a displacement of 1,800 cu. ft. being necessary in
case 1¹⁄₄-in. hose is used and 1,200 cu. ft. in case 1-in hose is used.
3. The great variation in the vacuum at the hose cocks which will admit
the passage of so much more air through a brush renovator on an outlet
close to the separator as to render useless the calculations already
made, or the high vacuum at the carpet or upholstery renovators would
render their operation practically impossible.
[Illustration: FIG. 64. ARRANGEMENT OF PIPING RECOMMENDED AS BEST FOR
PASSENGER CAR STORAGE YARD.]
Such a layout must be at once dismissed as impractical, and some other
arrangement must be adapted. The arrangement of piping shown in Fig. 64
is considered by the author to be the best that can be devised for this
case.
With this arrangement the vacuum at the separator must be maintained
at 11.50 in. mercury to insure a vacuum of 6 in. mercury at the outlet
“x” under the most unfavorable conditions, and the maximum variation
in vacuum at the inlets will be 3.45 in. mercury when 1¹⁄₄-in. hose
is used. This will give a maximum vacuum under a carpet renovator of
7¹⁄₂ in. mercury with 37 cu. ft. of air passing and will permit 70 cu.
ft. of free air per minute to pass a brush renovator when operating
with 100 ft. of hose attached to the inlet at which the highest vacuum
is maintained. Both of these conditions will permit satisfactory
operation and the increased air quantities will not seriously affect
the calculations already made. The maximum horse power required at the
separator will now be 20.5 as against over 50 in the case of the piping
arrangement shown in Fig. 63, and will require an exhauster having a
displacement of 950 cu. ft. instead of 1,800 cu. ft. required with the
former layout.
If 1-in. hose is used and 10 in. mercury maintained at the outlet “x”
under the same conditions as before, the vacuum at the separator will
be 14.50 in. and the maximum variation in the vacuum at the inlets will
be 3 in., which will give a maximum vacuum under a carpet renovator
of 6 in. mercury with 32 cu. ft. of air passing and will permit the
passage of 45 cu. ft. of free air through a brush renovator when
operated at the end of 100 ft. of hose attached to the outlet at which
the highest vacuum is maintained. This is a more uniform result, than
was noted when 1¹⁄₄-in. hose was used.
The maximum horse power which will be required at the separator will
now be 18.6 and the maximum displacement in the exhauster will be 740
cu. ft.
It is, therefore, evident that, where very long runs of piping are
necessary and where 100 ft. of hose will always be necessary, the
use of 1-in. hose will require less power and a smaller displacement
exhauster than would be required with 1¹⁄₄-in. hose, without affecting
the efficiency of the cleaning operations, and at the same time
rendering the operation of the renovators on extreme ends of the system
more uniform.
The example cited in Figs. 63 and 64 is not by any means an extreme
case to be met in cleaning systems for car yards, and the larger the
system the greater will be the economy obtained with 1-in. hose.
Such conditions, however, are confined almost entirely to layouts of
this character and will seldom be met in layouts within any single
building. This is fortunate, as the train cleaning is practically the
only place where the use of 100 ft. of hose can be assured at all times.
Very tall buildings offer a similar condition although the laterals are
now vertical and can be kept large enough to sufficiently reduce the
friction without danger of deposit of dirt in them, and the horizontal
branches will be short and also large enough to keep the friction
within reasonable limits without danger of deposit of dust.
Where large areas within one or a group of buildings must be served by
one cleaning system, better results can often be obtained by installing
the dust separator at or near the center of the system of risers
instead of close to the vacuum producer, as indicated in Fig. 65.
When this is done, the pipe leading from the separator to the vacuum
producer carries only clean air and can be made as large as desired and
the friction loss reduced, resulting in a considerable reduction in the
power required to operate the system.
[Illustration: FIG. 65. GOOD LOCATION FOR DUST SEPARATOR WHERE LARGE
AREAS ARE SERVED BY ONE CLEANING SYSTEM.]
Where the system becomes still larger, two or more separators located
at centers of groups of risers can be used and clean air pipes of any
desired size run to the vacuum producer (Fig. 66). When more than
one separator is used care should be exercised in proportioning the
pipe lines from the separators to the vacuum producer so as to have
the friction loss from the vacuum producer to each separator the same
in order to give uniform results at all inlets. This loss should
also be kept as low as possible in order to prevent a high vacuum
in a separator serving a portion of the system on which few sweepers
are in operation. If low friction losses in the clean air pipe will
require larger pipes than it is practical or economical to install,
pressure reducing valves might be located in the clean air pipes near
the separators to so regulate the vacuum at the separators and insure
uniform results. A system of this kind might serve several premises
and the air used by each be metered and the service sold much the same
as heat and electricity. However, the power required to operate the
system would be greater than that needed to operate a similar number
of sweepers by individual plants owing to the higher vacuum required
to overcome the friction in the trunk mains. This would be offset by
the use of larger units and the possibility of operating them at full
load at nearly all times. A system of this kind was contemplated in
Milwaukee some seven years ago, but was never installed.
[Illustration: FIG. 66. LOCATION OF SEPARATORS AT CENTERS OF GROUPS OF
RISERS FOR LARGE SYSTEMS.]
The question of pipe friction in connection with the design of vacuum
cleaning systems requires careful consideration, much more than it ever
received in the early days of the art and a great deal more than it
sometimes receives at the present time.
CHAPTER VIII.
SEPARATORS.
The appliances which remove the dust from the air current which has
carried it through the hose and pipe lines, in order to prevent damage
to the vacuum producer, play an important part in the make-up of a
vacuum cleaning system.
=Classification of Separators.=--Separators may be divided into two
classes according to their use:
1. Partial separators, which must be used in conjunction with another
separator in order to effect a complete removal of the dust from the
air. These separators are again divided into two sub-classes, _i. e._,
primary, or those removing the heavy particles of dust and dirt only,
and secondary, or those removing the finer particles of dirt which have
passed through the primary separator.
2. Complete separators, or those in which the removal of both the heavy
and the finer particles of dust is effected in a single separator.
Separators may also be classified, according to the method employed in
effecting the separation, into dry separators in which all operations
are effected without the use of liquid, and wet separators in which
water is employed in the removal of the dust.
=Primary Separators.=--Primary separators are nearly always operated
as dry separators and depend largely on centrifugal force to effect
the separation. The first type of primary separator used by the
Vacuum Cleaner Company is illustrated in Fig. 67. This consists of a
cylindrical tank, with hopper bottom, containing an inner cylinder
fixed to the top head. The dust-laden air enters the outer cylinder
near the top on a tangent to the cylinder. The centrifugal action set
up by the air striking the curved surface of the outer cylinder tends
to keep the heavy dirt near the outside of same, and as it falls
towards the bottom the velocity is reduced and its ability to carry
the dust is lost. When the air passes below the inner cylinder the
velocity is almost entirely destroyed and all but the very lightest of
the dust particles fall to the bottom, while the air and the light dust
particles find their way out of the separator through the opening in
the center at the top.
[Illustration: FIG. 67. EARLY TYPE OF PRIMARY SEPARATOR USED BY VACUUM
CLEANER COMPANY.]
[Illustration: FIG. 68. PRIMARY SEPARATOR USED BY THE SANITARY DEVICES
MANUFACTURING COMPANY.]
The primary separator used by the Sanitary Devices Manufacturing
Company is illustrated in Fig. 68. The inner centrifugal cylinder
is omitted and the air enters through an elbow in the top of the
separator, near its outer extremity, which is turned at such an angle
that the air is given a whirling motion resulting in the dust being
separated much the same as in the case of the Vacuum Cleaner Company’s
apparatus.
Either of these separators will remove from 95% to 98% of the dirt that
ordinarily comes to them through the pipe lines and are about equally
efficient.
[Illustration: FIG. 69. PRIMARY SEPARATOR USED BY THE GENERAL
COMPRESSED AIR AND VACUUM CLEANING COMPANY.]
[Illustration: FIG. 70. PRIMARY SEPARATOR MADE BY THE BLAISDELL
ENGINEERING COMPANY.]
The separator illustrated in Fig. 69 was used by the General Compressed
Air and Vacuum Cleaning Company. The entering air is led to the center
near the bottom and is then released through two branches curved
to give the air a whirling motion. The clean air is removed from
the center of the separator near the top. This separator is not as
effective in its removal of dirt as either of the former types, owing
to the entering air being introduced near the bottom. This tends to
keep the air and the dust in the bottom of the separator continually
stirred up, also the curved inlets give the air more of a radial than
a tangential motion and there is less separation due to centrifugal
action.
The separator illustrated in Fig. 70 is made by the Blaisdell
Engineering Company. In this separator the inner centrifugal cylinder
of the Vacuum Cleaner Company’s separator is replaced by a spiral
extending nearly to the outlet in the center of the top. This
arrangement tends to prevent the reduction in the air velocity and to
limit its effectiveness in the removal of dust.
Separators similar to the Sanitary separator have been manufactured by
many firms producing vacuum cleaning systems. These all differ somewhat
in details of construction but the principle involved, _i. e._,
centrifugal force and reduction in air velocity, is the same in all
cases.
With vacuum producers in which there are no close clearances or rubbing
contacts, these are the only separators used. The finer particles of
dust passing these separators are carried harmlessly through the vacuum
producer and through the exhaust to the outer atmosphere or to the
chimney or other flue where they are effectively sterilized.
=Secondary Separators.=--With vacuum producers having close clearances
or rubbing parts in contact with each other and the air exhausted,
further separation of the finer dust particles is necessary. To
accomplish this, secondary separators are used.
All of the early systems used a wet separator as a secondary separator.
That used by the Vacuum Cleaner Company is illustrated in Fig. 71.
It consists of a cylindrical tank partially filled with water, with
a diaphragm perforated in the central portion and fixed in place
below the water line, and an inverted frustrum of a cone placed just
above the water line. The air enters the separator below the water
line and passes up through the water in the form of small bubbles
which are broken up into still smaller bubbles on passing through the
perforations in the diaphragm. This action is very essential to the
thorough cleansing of the air, as large bubbles of air may contain
entrapped dust which will pass through the water and out into the
vacuum producer. The inverted frustrum of a cone is intended to prevent
any entrained water passing out of the separator with the air. This
separator has always given satisfactory results when used in connection
with reciprocating pumps.
The separator illustrated in Fig. 72 was manufactured by the General
Compressed Air and Vacuum Cleaning Company. The air enters the
separator through the pipe curved downward and escapes at the center
below the water line. It then rises in the form of bubbles and most of
it strikes the under side of the ribbed aluminum disc “a,” which is
intended to float on the surface of the water, and passes along the
ribbed under surface of this disc, escaping into the upper part of the
separator around the edge.
[Illustration: FIG. 71. SECONDARY SEPARATOR USED BY THE VACUUM CLEANER
COMPANY.]
[Illustration: FIG. 72. SECONDARY SEPARATOR USED BY THE GENERAL
COMPRESSED AIR AND VACUUM CLEANING COMPANY.]
The clean air passes out of the top of the separator to the vacuum
producer. The successful operation of this separator is dependent on
the freedom of motion of the disc “a,” which will always keep it on
the surface of the water, and on all of the air passing up through the
water under the disc.
Should the disc become caught on the supporting pipe the violent
agitation of the water, which occurs when the system is in operation,
will cause the disc to be left high and dry above the water at times,
and submerged at other times. When this disc is above the water line
it will not break up any of the large bubbles. Also, when there is a
large quantity of air passing through the separator, there is great
likelihood that considerable of the air bubbles will pass up through
the water entirely outside of the disc and these bubbles will not be
broken up. This separator has given somewhat unsatisfactory results in
some installations tested by the author.
[Illustration: FIG. 73. SECONDARY SEPARATOR USED BY THE SANITARY
DEVICES MANUFACTURING COMPANY.]
[Illustration: FIG. 74. TYPE OF DRY SEPARATOR USED AS SECONDARY
SEPARATOR.]
The separator used by the Sanitary Devices Manufacturing Company
differs from those already described in that the air and water are
mixed before they enter the separator and the air comes into the
separator above the water line. The air enters the pipe “a” (Fig. 73)
and passes to the aspirator “b,” which is connected to the separator
by the pipe “d” below the water line and the pipe “e” above the water
line. The excess of vacuum in the separator draws the water out of
the aspirator and its pipe connections until the water line in this
pipe is lowered below the top of the horizontal portion of the piping,
when the air bubbles up through the demonstrator glass “c” and passes
into the separator through the pipe “e.” The filling of the vertical
pipe leading to “c” with air causes the static head of the water in
the separator to produce a flow of water through the pipe “d” into
the aspirator “b.” This is formed in the shape of a nozzle and the
water enters in the form of a spray and thoroughly mixes with the air.
The cleansing action of this water spray has been found to be very
effective in removal of all fine dust and this separator has been found
to be the most effective wet separator ever produced.
While the wet separator when properly designed will effectively remove
the finest of dust, greasy soot will not emulsify with the water and
its removal is practically impossible. Fortunately, this form of
material in the finely-divided condition in which it passes the primary
separator is not gritty and does not produce injurious effect on the
vacuum producer.
The wet separator is also at a disadvantage in that there is a loss
of vacuum in passing through same equal to the head of water that is
carried between the inlet and the surface of the water. This generally
amounts to nearly 2 in. mercury.
Means must be provided to observe the height of the water in the wet
separator. For this purpose a glass window in the side of the separator
has been found to be the most effective. The use of an ordinary gauge
glass such as is used on boilers has been tried, but it has been found
that they readily become so clouded by the action of the muddy water
as to render them useless while the constant agitation of the water
against the window when the system is in operation tends to keep the
glass clean.
Dry separators have been used for secondary separators to a limited
extent. All of these contained a bag made of canvas or some other
fabric. The separator illustrated in Fig. 74 contains a bag made of
drilling which is slightly smaller than the inner diameter of the
cylindrical casing of the separator. The air enters the inside of the
bag, inflating it, and passes through the bag and out through the
opening in one side of the casing. A wire guard is placed over this
opening to prevent the bag being drawn against the opening and thus
rendering only a small portion of it effective.
These bags offer very little resistance to the passage of the air when
they are clean but they soon become filled with dust and produce an
increased resistance which, if neglected, may result in so great a
difference in pressure as to hinder the action of the system and result
in the rupture of the bag, letting the dust into the vacuum producer.
Some trouble has been experienced in finding a suitable material
through which the dust will not pass. Hush cloth, such as used on
dining tables, has been found to be the best material for this
purpose. Better results are obtained by passing the air from the
outside of the bag towards the inside than when the air is passed as
indicated in Fig. 74. When this arrangement is adopted, it is necessary
to stretch the bag over a metal screen or frame in order to prevent
collapse.
=Complete Separators.=--Complete separators are of two classes,
_i. e._, dry and wet. The first complete separator that the author
has knowledge of was used by the Vacuum Cleaner Company, in the
form of a cylindrical tank and contained centrifugal cylinder and
also a perforated plate. It was practically a combination of the
separators indicated in Figs. 67 and 71. This separator was installed
in connection with a small rotary pump and mounted on a truck. It
worked very well until it became filled with dirt when, in one case,
the entire contents were ejected into an apartment in which it was
being used. This separator was then rebuilt in the form shown in Fig.
75, the bag being made of hush cloth stretched over a wire screen.
The air enters the cylinder tangentially and much of the separation
is accomplished by centrifugal force, the remainder of the dust
being removed as the air passes through the bag. This separator was
successfully used as long as this company continued to manufacture such
apparatus.
Another form of complete separator quite similar to that above
described has recently been brought out by the Electric Renovator
Manufacturing Company and is shown in section in Fig. 76. The air
enters this separator tangentially below the line of the dust bag,
which is made of muslin folded back and forward over a set of
concentric cylinders thus giving a large area for the passage of the
air. Being entirely above the line of the entering air, none of the
heavy dirt strikes the bag and what dirt is caught on the bag is on the
lower side of same and is shaken off every time the bag is agitated.
This agitation occurs every time there is any change in the volume
of air passing the separator, and when these separators are used in
connection with fan type of exhausters there is a constant surging
whenever the exhauster is operated with a small volume of air passing.
This tends to keep the bag clean automatically.
[Illustration: FIG. 75. FORM OF COMPLETE SEPARATOR USED BY THE VACUUM
CLEANER COMPANY.]
The separator illustrated in Fig. 77 is manufactured by the American
Radiator Company. The air enters this apparatus through the pipe in
the center and passes directly down to the bottom, the velocity being
gradually reduced due to the expansion of the air as it passes down the
cone-shaped inlet, the heavy dirt falling to the bottom. The air then
passes up along the inner surface of the cylindrical shell and thence
through the bag, which is stretched over a screen, to the outlet. In
this separator we see the first case in which centrifugal action is not
utilized in separating the heavy dust, the makers evidently considering
the reduction of air velocity and the action of gravitation to be
ample. This bag is arranged to permit the air passage from the outside
towards the inside and it is tapered to allow the dirt to fall off.
The vacuum gauge is connected to the inner and outer sides of the bag
by means of a three-way cock to permit of measuring the difference in
vacuum between the inside and outside of the bag to determine when the
bag is in need of cleaning, which is accomplished by a reversal of the
air current through the bag. This is quite necessary in order to keep
the separator always in an efficient condition.
[Illustration: FIG. 76. COMPLETE SEPARATOR BROUGHT OUT BY THE ELECTRIC
RENOVATOR MANUFACTURING COMPANY.]
[Illustration: FIG. 77. COMPLETE SEPARATOR MADE BY THE AMERICAN
RADIATOR COMPANY.]
A separator was devised by the Sanitary Devices Manufacturing Company
in which the bag was held extended by a wire ring having a weighted rod
passing out through the top of the separator attached thereto. When
the bag became clogged the difference in pressure on the two sides
would result in a tendency of the bag to collapse and the rod would be
raised up out of the separator, indicating that cleaning was necessary,
which could be easily accomplished by drawing the rod up and down a few
times thus shaking the dust off the bag. This separator never came into
general use, although its arrangement was ingenious and should have
been easy to operate.
The great difficulty with all bags which must be cleaned periodically
is that they are almost universally neglected even when there is a
visual indicator to show the accumulation of dirt, and when it becomes
necessary to manipulate a three-way cock in order to ascertain when
this cleaning must be done it will seldom if ever be attended to. A bag
that will clean itself, such as the Capitol Invincible, is shown in
Fig. 76.
The separator used by one manufacturer consists of a simple cylindrical
tank into which the air is blown tangentially, with a screen near the
top, the whole forming a base for the vacuum producer. This separator
does not remove any but the heaviest dirt and is suitable for use only
with a vacuum producer having very large clearances and in locations
where the discharge of considerable dirt into the atmosphere is not
objectionable.
=Total Wet Separator.=--The only total wet separator which is in
commercial use is manufactured by the American Rotary Valve Company.
This separator is contained in the base of the vacuum producer and is
provided with a screen near the point of entrance of the dust-laden
air, which screen is cleaned by a mechanically-driven bristle brush.
When the water in the separator becomes foul, the contents of the
separator are discharged direct to the sewer by means of compressed
air. If this separator receives proper attention it makes the most
sanitary arrangement that has been introduced in the vacuum cleaning
line to date. However, the separator should be emptied at frequent
intervals or the volume of solid matter contained in the same will
become so great that there will not be enough water present to flush
the sewer and stoppage is likely. These separators are often neglected
until the contents become of the consistency of mortar or molasses
which is not a fit substance to discharge into a sewerage system.
There is still another form of apparatus used in connection with vacuum
cleaning systems which should be called an emulsifier rather than a
separator. That is the type used with the Rotrex and the Palm systems.
The dust is mixed with water when it first enters the pump chamber,
a screen being used to remove the lint and larger particles of dirt
and then the mud produced by the combination of the dust and water is
passed through the pump along with the air. The air and muddy water are
separated on the discharge side of the vacuum producer. In many cases
where the exhaust pipe is long, there is considerable back pressure on
the discharge which is often sufficient to force the seals in traps
on the sewerage system, allowing sewer gas to be discharged into the
building in which the cleaning system is installed. No means are
provided for automatically cleaning the screen used in these appliances
and the author knows of cases where the screen has become so completely
clogged with lint that its removal from the machine was necessary in
order to render the operation of the cleaning tools possible.
When dry separators are used, the manual removal of the dry dirt
accumulated is necessary and is an objectionable as well as unsanitary
operation. The author considers that the ideal arrangement of
separator would be one in which the dirt can all be emulsified with
water and retained in the separator, only the air passing through the
vacuum producer, and in which the contents of the separator would be
discharged automatically to the sewer when the density of this mixture
becomes as heavy as will readily run through the sewer. This discharge
should be of sufficient volume to completely fill an ordinary house
sewer in order to insure a thorough flushing of the drain, and should
be discharged into the sewer under atmospheric pressure in order
to guard against the forcing of water seals in any of the plumbing
fixtures.
[Illustration: FIG. 77a. INTERIOR CONSTRUCTION OF DUNN VACUUM CLEANING
MACHINE.]
A separator of this type has recently been patented by E. D. Dunn,
originator of the Dunn Locke system. It is illustrated in Fig. 77a. The
action of the separator is as follows: After starting the motor and
turning on a small quantity of water, a vacuum is produced in one tank
and through a system of piping to the cleaning implement in use. The
dust and dirt collected by the implement is saturated as it approaches
the plant and in this saturated condition enters the bottom of a body
of water in the tank.
When the accumulating dirt and water reach a certain level a valve
is automatically operated which closes the tank’s communication with
the vacuum pump and allows its contents to flow off to the sewer by
gravity. The mechanism for operating the valve is rather unique and
includes a float which, on rising with the water, makes a positive
electrical contact, as shown in the figure. In this illustration one
tank is about to discharge and the other tank is about to become
operative. The electrical contact causes the core of the magnet at O¹
to rise, making the lever, K, turn over, which action opens one valve
and closes the other. In this way the tanks alternately partly fill and
empty their collections of water and sweepings.
This system has not as yet been in commercial use for a sufficient
length of time to insure its successful operation, and the author does
not consider the passing of dirt and water through ordinary check
valves to be commercially possible without rendering these checks
inoperative.
Check valves have been used where partial wet and dry separators are
operated in tandem to prevent drawing water into the dry separator,
in the event of the plant being shut down with all inlets on the pipe
line closed. In such a case, the leakage through the pump into the wet
separator may raise the pressure in this separator faster than leakage
on the pipe line raises the pressure in the dry separator.
This is accomplished by providing a small connection between the upper
part of the two separators, fitted with a check valve opening towards
the dry separator. When the vacuum producer is in operation, the
vacuum in the wet separator is approximately 2 in. greater than that
in the dry and the check is held closed. When the vacuum producer is
stopped and the vacuum in the wet separator falls faster than in the
dry separator, this check opens and clean air passes from the wet to
the dry separator. When operating under these conditions, the action of
the check valve is satisfactory. However, the author has known of cases
where the check leaked and when this happened the check was immediately
clogged by the dust-laden air from the dry separator.
CHAPTER IX.
VACUUM PRODUCERS.
The next portion of the cleaning system is that which produces the
motion of the air through the system and that to which the motive power
is applied, namely, the vacuum producer.
=Types of Vacuum Producers.=--Vacuum producers can be divided into
general classes: 1. Displacement type, in which a constant volume
of air is displaced during each complete cycle of operations of the
machine, and 2. Centrifugal type, in which the volume of air passing
the producer during each complete cycle of operations varies with the
resistance to the passage of such air through the system.
=Displacement Type.=--Under this head the piston and rotary pumps
are classed, and they are subdivided according to construction into
reciprocating and rotary, valved and valveless, air cooled and water
cooled.
=Centrifugal Type.=--Under this head the fan type of vacuum producers
are classed. They may be divided, according to construction, into
single stage and multi-stage, horizontal and vertical.
=Power Required to Produce Vacuum.=--In order to ascertain the
efficiency of the various types of exhausters to be discussed in this
chapter it is necessary to ascertain the actual power necessary to move
one cubic foot of free air at any degree of vacuum.
As nearly all machines tested by the author were driven by electric
motors and the power was, therefore, indicated in watts, the curve C-D
in Fig. 78 showing the actual power necessary to exhaust one cubic
foot of free air at the vacuum noted in the lower margin, assuming no
clearance and adiabatic compression, is used as a basis for calculation
of efficiency. This shows that to produce a vacuum of 8 in. mercury
there will be required an expenditure of 16 watts for each cubic foot
of free air exhausted, and to produce a vacuum of 12 in. mercury will
require an expenditure of 27 watts. If these quantities be divided
by the efficiency of the machine the actual power required will be
determined.
[Illustration: FIG. 78. POWER CONSUMPTION AND EFFICIENCY OF AIR
COMPRESSOR USED AS A VACUUM PUMP.]
=Reciprocating Pumps.=--The reciprocating pump was used on the majority
of the earlier vacuum cleaning systems. The most common form in early
use was a commercial air compressor which was used as a vacuum pump
without any change in its construction. It was usually fitted with
mechanically-operated induction and poppet type of eduction valves
of heavy pattern, fitted with cushions of the dash pot principle,
the same as are used on air compressors working against terminal
pressures as high as 100 lbs. per square inch. The cylinders were water
jacketed to remove the heat of high compression. The valves in these
compressors were heavy and required considerable pressure to open them
and the friction of the valve gear and other moving parts, which were
made heavy enough to withstand the strains of high compression, was
excessively high for a machine where the compression did not exceed 8
or 9 lbs. per square inch. Their efficiency, therefore, is lower under
actual operating conditions than if they were working against pressures
for which they were designed. A curve of the power consumption of a
14-in. × 8-in. Clayton compressor is shown on Fig. 78, the abscissae
being the vacuum in inches of mercury and the ordinates of curve “AB”
the watts required to exhaust one cubic foot of free air. Curve “cd”
represents the theoretical watts required to do the same work. These
compressors were used in connection with systems operating with 1-in.
hose and the vacuum usually carried was 15 in. mercury. They require
approximately 77 watts per cubic foot of free air at this vacuum and
the efficiency, shown in curve “ce” (Fig. 78) is 46%.
[Illustration: FIG. 79. MODIFICATION OF RECIPROCATING PUMP MADE BY THE
SANITARY DEVICES MANUFACTURING COMPANY.]
Were this compressor used in connection with a system operating through
1¹⁄₄-in. hose and a vacuum of 8 in. mercury maintained, the efficiency
would drop to 31%.
A modification of the reciprocating pump was manufactured by the
Sanitary Devices Manufacturing Company in which light-weight poppet
valves placed in the heads of the cylinder were used, as indicated in
Fig. 79. Curves of the watts per cubic foot and efficiency of this
type of compressor are shown in Fig. 80. It will be noted that this
compressor shows a better efficiency than the air compressor at all
degrees of vacuum and it is the best reciprocating pump that the writer
has ever tested.
This pump was made for several years without water jacket and no
trouble was ever experienced with overheating. However, owing to the
commercial air compressors being jacketed, the makers using same made
this a talking point and this company was obliged to jacket its pumps.
[Illustration: FIG. 80. POWER CONSUMPTION AND EFFICIENCY OF MODIFIED
RECIPROCATING PUMP.]
The Vacuum Cleaner Company used a Clayton pump on its smaller plants
which was fitted with a semi-rotary valve in each end serving as an
induction and eduction valve, while the heavy poppet eduction valve of
the air compressor was dispensed with. The increase in efficiency that
should have resulted from this change was not realized. The reason for
this can be more readily seen by inspection of the indicator cards,
Figs. 81 and 82.
Fig. 81 is a card taken from one of the Clayton compressors fitted
with combined induction and eduction valves, and Fig. 82 a card from a
compressor with light steel induction and eduction valves of the poppet
type.
It will be noted that the compression line, a-d, Fig. 81, extends above
the atmosphere line, the pressure at the time of opening the eduction
valve being 4 lbs. per square inch above the atmosphere. This is due
to the failure of the mechanically-operated valve to open soon enough.
This valve being also the induction valve, it is necessary for the
eduction port to be closed before the induction port can be opened, in
order to prevent a short circuit of air from the atmosphere into the
separators. This fact is responsible for the sudden increase in the
pressure at b, the eduction port having closed before the completion of
the stroke and the air in the clearance space being compressed to 6¹⁄₂
lbs. above atmosphere. The induction port is not opened until after the
beginning of the suction stroke resulting in the high degree of vacuum
at c.
[Illustration: FIGS. 81 AND 82. INDICATOR CARDS FOR CLAYTON AND
MODIFIED PUMPS.]
Compare this with the card, Fig. 82. Here the compression does not
extend above the atmosphere line more than ¹⁄₄ lb. per square inch and
the eduction valve does not close until the end of the stroke so that
the vacuum at the beginning of the suction stroke is no lower than
during the entire stroke.
These pumps were working under the same conditions, _i. e._, 15-in.
vacuum in the separator. The M. E. P. for Fig. 81 is 7.05 while that in
Fig. 82 is 6.7 and is higher than is usually the case with this pump,
due to the fact that the exhaust pipe from this pump was very long and
crooked, a condition which should be avoided whenever possible. Also,
the pump from which this card was taken is one of the older pattern and
the clearance was greater than in the later models. The point at which
the eduction valve opens in Fig. 81 is 53% of the stroke and it closes
at 95% of the stroke and is, therefore, open 42% of the stroke, while
in Fig. 82 the eduction valve opens at 46% of the stroke and remains
open to the end of the stroke, and, therefore, is open for 54% of the
stroke. Thus the pump with the poppet valves will move more air at
the same vacuum with less expenditure of power than the pump with the
mechanically-operated valves.
Another type of reciprocating pump has been introduced in the past two
or three years in which a single valve which rotates continuously in
one direction is used for induction and eduction valve, for both ends
of the cylinder. This valve is a plain cylindrical casting having ports
cored through to alternately connect the cylinder ports with the intake
and exhaust ports.
By rotating this valve 180° on its stem the vacuum pump is changed to
an air compressor. This arrangement is adopted in order to discharge
the contents of the separator into the sewer as was explained in
Chapters I and VIII. In this pump there must be points at which both
the induction and eduction valves are closed at the same time and
results similar to those found with the semi-rotary valves of the
Clayton pump will naturally be in evidence. The author has endeavored
to obtain an indicator card from one of these pumps but has been
unable to do so. The effect of simultaneous closing of both induction
and eduction ports would naturally be more marked in this pump than
in the Clayton, as the motion of the valve in this case is uniform at
all times while the motion of the valve gear of the Clayton pump is so
arranged that the valve moves very fast at the time that both ports are
closed. One of the two pumps of this type which was recently installed
in the New York Post Office is illustrated in Fig. 83. These pumps have
a displacement of 1,200 cu. ft. each and are the largest reciprocating
pumps in use for vacuum cleaning at this writing.
An interesting property of the piston pump which lends itself to the
economical control of the vacuum in the system is illustrated by the
curve at the top of Fig. 78 which shows the total power required to
operate the Clayton type air compressor, the efficiency of which is
indicated by the lower curves on this figure. The compressor was
operated at constant speed and the air volume varied to give various
degrees of vacuum from atmospheric pressure to a closed suction and
the power to operate the compressor read at intervals of two inches.
The current input to the motor in amperes is indicated by ordinates
and the vacuum in the separator by the abscissae. This indicates that
the piston pump requires the maximum power to operate at about 15-in.
vacuum and that the least power is required when the vacuum is at the
highest point possible to obtain. The method employed in utilizing this
characteristic of a piston pump will be discussed in a later chapter.
[Illustration: FIG. 83. ONE OF THE PUMPS INSTALLED IN CONNECTION WITH
THE VACUUM CLEANING SYSTEM IN THE NEW YORK POST OFFICE, THE LARGEST
RECIPROCATING PUMP USED FOR THIS PURPOSE UP TO THE PRESENT.]
=Rotary Pumps.=--The Garden City rotary pump is a good example of the
single-impeller type of pump and is or has been used to some extent
by at least two makers of vacuum cleaning systems. Its interior
arrangement is shown in Fig. 84. A solid cylindrical impeller, A, is
mounted eccentrically in the cylindrical outer casing, the impeller
being fitted with four sliding vanes which are provided with distance
pieces, E, and wearing faces, B. The oil reservoir is provided with
a needle valve which is automatically opened as soon as there is any
vacuum produced and closes automatically when the machine is shut down.
The rate of feed of oil is adjusted by the screw I. This type of pump
offers a large surface in rubbing contact with the case and becomes
very hot when in operation. It requires liberal lubrication in order
to prevent heating and cutting of the surface of the casing. End wear
in these pumps causes leakage, and, as usually constructed, there are
no means provided for taking up this wear. It can be provided for,
however, by using metal shims on the ends of the cylindrical casing.
[Illustration: FIG. 84. INTERIOR ARRANGEMENT OF THE GARDEN CITY ROTARY
PUMP.]
[Illustration: FIG. 85. POWER REQUIRED TO OPERATE GARDEN CITY TYPE OF
ROTARY PUMP.]
The power required to operate this type of pump (Curve a-b, Fig. 85),
is nearly the same as that required to operate a piston pump for vacuum
less than 12 in. mercury, but when the vacuum becomes higher, the power
required becomes much greater than that required by the piston pump.
The efficiency (Curve c-e, Fig. 85), is identical with that obtained
with the light-weight poppet valve pump (Curve c-e, Fig. 80) from 0 to
11 in. vacuum, but for higher vacuum the efficiency of this type of
pump falls off, while the efficiency of the piston pump becomes greater
as the vacuum becomes higher. This difference in the characteristics
of the two types of pumps is due to the presence of valves in one case
and their absence in the other. With the piston pump the atmospheric
pressure reaches the cylinder only while air is being discharged, the
eduction valves being closed at other times and a partial vacuum exists
on both sides of the piston. The higher the vacuum produced, the less
time there is atmospheric pressure on the piston until, when no air is
discharged, the air contained in the clearance space of the cylinder
is compressed and expanded, the compression and expansion lines being
coincident. The indicator card will have no area, and the only power
expended is that required to overcome the friction in the moving
parts. With the rotary pump there are no discharge valves to hold the
atmospheric pressure from the discharge side of the impeller and the
compression of the rarified air is accomplished by the atmospheric
pressure admitting air through the eduction port into the chamber. As
it comes opposite the eduction port there is no difference in the time
during which the impeller is subject to atmospheric pressure, no matter
what the quantity of air being discharged. The higher the vacuum in the
spaces containing rarified air, the greater the difference in pressure
on the opposite sides of the sliding vane and, therefore, the greater
total power required to turn the rotor.
[Illustration: FIG. 86. ARRANGEMENT OF DOUBLE-IMPELLER ROOT TYPE ROTARY
PUMP FOR VACUUM CLEANING WORK.]
Another type of rotary pump which is fast becoming the most popular is
the double-impeller type. This is generally known as the Root blower,
as the firm of this name was the first to manufacture same. They have
been in use for many years as blowers for gas works, and as vacuum
producers for various purposes, mainly the operation of pneumatic tube
systems.
Why this form of vacuum producer was not earlier adopted in vacuum
cleaning systems, instead of the sliding-vane type, is hard to
understand. This pump contains two impellers or cams which are mounted
on shafts geared together and revolve in opposite directions inside of
a case, always being in close proximity to the case and to each other,
but never touching. They are, therefore, frictionless in operation and
the introduction of a small amount of water renders them practically
air tight. There being no metallic contact between the moving parts,
internal lubrication is unnecessary and there is no wear on either the
impellers or the casing and no means of taking up wear are necessary.
The arrangement of the impellers and the method of providing water to
seal the parts is shown in Fig. 86. A reservoir containing water is
provided on the discharge side of the pump and a small pipe leads from
this reservoir to the suction side of the pump. The vacuum lifts water
from the reservoir and discharges same in a spray into the suction
chamber. This water passes through the pump and is separated from the
air in the discharge chamber to be returned to the suction chamber by
the vacuum. This operation will start automatically as soon as any
degree of vacuum is formed and will cease as soon as the pump is shut
down.
[Illustration: FIG. 87. ROTARY PUMP ARRANGED WITH DOUBLE-THROW SWITCH
FOR REVERSING PUMP.]
Any of these rotary pumps having no valves can be changed to an air
compressor by reversing the direction of rotation. This is adapted
by the American Rotary Valve Company in connection with their wet
separators to discharge the contents of the separator into the sewer,
on all of their smaller-sized plants. Fig. 87 shows one of these plants
arranged with double-throw switch for reversing the electric motor used
to operate the pump and also shows the arrangement of the rotary brush
which is used to clean the screen in the wet separator, as has been
explained in Chapter VIII.
[Illustration: FIG. 88. POWER CONSUMPTION AND EFFICIENCY ROOT TYPE OF
PUMP.]
[Illustration: FIG. 89. THE ROTREX VACUUM PUMP, USED BY THE VACUUM
ENGINEERING COMPANY.]
The power consumption and efficiency of this type of pump are shown in
Fig. 88. The watts per cubic foot of free air (Curve a-b) show a much
lower consumption of power at the lower vacuum than any of the pumps
already tested. This is probably due to the fact there is no internal
friction. It will be noted that the power to operate at no vacuum is
but 10 watts per cubic foot of free air, while all the others require
from 24 to 34 cubic feet. This also results in the efficiency curve
(c-e, Fig. 88) reaching its maximum value at a lower vacuum than in the
case of the sliding vane pump (Fig. 85).
[Illustration: FIG. 90. LATE TYPE OF CENTRIFUGAL EXHAUSTER MADE BY THE
SPENCER TURBINE CLEANER COMPANY.]
The efficiency is fairly constant between 6-in. and 10-in. vacuum and
is much higher than is obtained with any of the other types of pumps at
these vacua. When they are operated at higher vacuum the efficiency is
about the same as obtained with the sliding vane pumps and lower than
that obtained with the reciprocating pumps. The best efficiency of this
pump is at the vacuum necessary to operate a cleaning system provided
with 1¹⁄₄-in. hose.
A slight modification of this type of pump is that used by the Vacuum
Engineering Company, known as the Rotrex. This pump has but one
impeller, of nearly the same form as the impellers in the Root blowers
and has a follower driven by crank and connecting rods which is always
in close proximity to the impeller but does not touch same. The
arrangement of this pump is illustrated in Fig. 89 which also shows
the saturation chamber and screens used instead of a separator, as
explained in Chapter VIII.
[Illustration: FIG. 91. POWER AND EFFICIENCY CURVES FOR THE SPENCER
MACHINE.]
The author has never tested the economy of these pumps but would infer
that their economy should be about the same as that of the Root blower.
=Centrifugal Exhausters.=--This type of exhauster has always taken
the form of a fan. The first stationary fan type of exhauster was
manufactured by the Spencer Turbine Cleaner Company. Their latest type
is illustrated in Fig. 90. It consists of a series of centrifugal
fans mounted on a vertical shaft, stationary deflection blades being
provided between the wheels to conduct the air from the periphery of
one wheel to the center of the next.
[Illustration: FIG. 92. INTERIOR ARRANGEMENT OF INVINCIBLE MACHINE,
MANUFACTURED BY THE ELECTRIC RENOVATOR MANUFACTURING COMPANY.]
These centrifugal exhausters do not have a positive displacement, as do
all those already described, and therefore the variation of the vacuum
is not as much as in case of the positive displacement machines. The
vacuum produced when the machine is moving no air is slightly less
than the maximum that the exhauster can produce and there is very
little variation in the vacuum with air quantities which can be moved
without exceeding the capacity of the motor or other means producing
the power. The curves showing the power required to operate and the
efficiency of this type of vacuum producer are, therefore, plotted
with abscissae representing the air moved in cubic feet per minute.
The vacuum produced and the power required to operate are plotted as
ordinates. The curves for the Spencer machine are shown in Fig. 91.
This curve is taken from a four-sweeper machine and the vertical lines
numbered 1 to 4 represent the conditions when that number of sweepers
are in operation; that is, bare floor renovators, with 50 ft. of hose
or 80 cu. ft. of free air per minute. The maximum efficiency is reached
at full load and is approximately 42%. The vacuum at this efficiency is
5¹⁄₂ in. mercury, a drop of ³⁄₄-in. from the maximum which was obtained
at one-fourth load.
[Illustration: FIG. 93. POWER CONSUMPTION. VACUUM AND EFFICIENCY OF
FIRST TYPES OF INVINCIBLE MACHINE.]
These machines have rather large clearances and a preliminary separator
is all that is required. They operate at a speed of about 3,600 R. P.
M. and the peripheral speed of the fans varies from 15,000 to 22,000
ft. per minute. This produces some noise and considerable vibration
and care must be exercised in mounting the machine. In order to insure
quiet running the usual method is to place the machine on a felt pad of
considerable thickness.
[Illustration: FIG. 94. POWER CONSUMPTION, VACUUM AND EFFICIENCY OF
INVINCIBLE MACHINE AFTER VALVE WAS FITTED TO DISCHARGE.]
The machines made by the Electric Renovator Manufacturing Company are
horizontal and have much smaller clearances than the Spencer machines.
They operate at approximately the same rotary and peripheral speed
and are, therefore, as noisy. However, the center of gravity of these
machines is lower and the vibration is not so great. The Spencer
Company is now making a horizontal machine which it furnishes only when
required, the claim for their vertical machine being that the weight
of the moving parts counteracts the thrust of the atmospheric pressure
against the fans and relieves the work of the thrust bearings, at the
expense of greater vibration. With ball bearing thrusts, the author
does not consider this to be of great importance.
A view of the interior arrangement of the Invincible machine, as
manufactured by the Electric Renovator Manufacturing Company, is shown
in Fig. 92.
These machines, when first made, were without valves and the power
consumption, vacuum and efficiency are shown in Fig. 93. It will be
noted that the vacuum produced, when the machine is operated at or
below one-half load, is considerably lower than is obtained at greater
loads. This characteristic produces a disagreeable noise when the
machine is not handling any air, evidently due to air rushing back
through the outlet when the vacuum tends to build up to the maximum
which occurs at intervals of about one-half second.
[Illustration: FIG. 95. FOUR-SWEEPER INVINCIBLE PLANT INSTALLED IN THE
UNITED STATES POST-OFFICE AT LOS ANGELES, CAL.]
In order to overcome this trouble a valve has been fitted to the
discharge, as indicated at 4, Fig. 92. With this valve in place the
power consumption, efficiency and vacuum are as shown in Fig. 94. It
will be noted that the vacuum is as high at no load as at any load up
to full load and is practically constant. The efficiency at light loads
is the same as before but it is slightly lower at full load, being 50%
without the valve and 47% with the valve. This is due to the power
being expended in opening the valve for large quantities of air and to
friction in the valve passage.
A four-sweeper plant of this manufacture is shown in Fig. 95. This
plant is installed in the United States Post Office at Los Angeles,
Cal. The separate centrifugal separator, shown at the left of the cut,
is not used in the regular equipment and was added in this case to
fulfill the specification requirements.
A centrifugal pump with a single impeller is manufactured by The United
Electric Company and is known as the Tuec system. A phantom view of
the pump and separator is shown in Fig. 96. It will be noted that the
shaft is vertical. However, the vacuum is under the impeller in this
case, and the thrust due to the atmospheric pressure is down instead of
up, as in the case of the Spencer machines. This throws the weight of
the parts, plus the thrust due to atmospheric pressure, on the thrust
bearing. These machines do not produce a vacuum greater than 3-in.
mercury, and the additional thrust is not as great as in the case of
the machines producing higher vacuum, the impeller being 24 in. in
diameter, its area 450 sq. in. and the thrust, with a vacuum of 3-in.
mercury, 675 lbs., which is worth considering. This downward thrust
is partially counterbalanced by mounting the armature of the electric
motor used to operate the fan, slightly below the magnetic center,
thereby causing an upward magnetic pull. These machines are intended to
be used with large hose and pipe lines to reduce the friction to a very
low point. When operating carpet renovators the vacuum at the renovator
rises to 1-³⁄₄-in. mercury and the type of renovator used by them
passes approximately 50 cu. ft. of air, while the bare floor renovators
pass approximately 95 cu. ft. They are extensively used where bare
floor work is required, their first cost being low.
The results of tests of two of these machines of four-sweeper capacity,
driven by alternating and direct-current motors, respectively,
are shown in Fig. 96a. These curves indicate a considerably higher
efficiency with the alternating than with the direct-current
motor. This is due to the low efficiency of the special high-speed
direct-current motors used with all centrifugal fan-type exhausters.
The alternating-current motors are not so affected, in fact, the speed
at which these fans are operated is fixed by the requirements of the
alternating-current motors.
[Illustration: FIG. 96. CENTRIFUGAL PUMP WITH SINGLE IMPELLER,
MANUFACTURED BY THE UNITED ELECTRIC COMPANY.]
The efficiency of the other types of centrifugal exhausters (Figs. 91,
93 and 94) is in every case accomplished with direct-current motors.
This machine has an efficiency about the same as the Spencer machine.
It will be noted that the vacuum produced does not fall off as the load
increases, as in the case of the multi-stage fans. This characteristic
is probably due to the fact that there is no wire drawing in the
diversion vanes, as in the case of the multi-stage exhauster.
[Illustration: FIG. 96a. TEST OF CENTRIFUGAL PUMP WITH SINGLE IMPELLER.]
=Steam Aspirators.=--The steam aspirator as a vacuum producer in
connection with vacuum cleaning systems was first used by the American
Air Cleaning Company, and has been used to a limited extent by the
Sanitary Devices Manufacturing Company. The type of apparatus used by
the American Air Cleaning Company is illustrated in Fig. 97. A single
partial separator is used with this system and the lighter dust is
allowed to pass through the aspirator, where it is mixed with the
steam and sterilized. The aspirator is in the form of an ejector, with
a specially designed nozzle, and is always fitted with an automatic
device for cutting off the steam when the vacuum in the separator
reaches the degree desired.
[Illustration: FIG. 97. STEAM ASPIRATOR USED BY THE AMERICAN AIR
CLEANING COMPANY.]
The steam consumption required to exhaust 1 cu. ft. of free air at
various vacua, as determined by actual test of four different nozzles,
is shown in Fig. 98, the steam being the actual weight of dry and
saturated steam at the gauge pressures noted. The American Air Cleaning
Company used to guarantee a steam consumption of 250 lbs. per hour from
and at 212° F., assuming that the feed water temperature was 32° F.,
the vacuum to be maintained at 9 in. mercury at the aspirator.
Taking the results of the test of the three-sweeper nozzle as an
average, 0.066 lbs. of steam will be required to exhaust 1 cu. ft. of
free air at 9 in. vacuum. The total heat in 1 pound of dry steam at 110
lbs. gauge is 1187 B. T. U. and at 212° F. the latent heat is 970 B.
T. U. The factor of evaporation, therefore, is 1.235, and the weight of
steam at 110 lbs. allowed by the guarantee is 202 lbs. This amount of
steam will exhaust 3,060 cu. ft. per hour, or 51 cu. ft. per minute,
which is more than sufficient to operate a carpet renovator, and is a
little less than will pass through a bare floor brush attached to the
end of 50 ft. of 1 in. diameter hose, if the hose is attached directly
to the aspirator. With a line of pipe between the hose cock and the
aspirator, the air quantity will be somewhat less, and this guarantee
will undoubtedly be fulfilled in every case.
[Illustration: FIG. 98. STEAM CONSUMPTION OF STEAM ASPIRATOR.]
The advisability of using an aspirator will depend on the conditions
to be met at the building in each case. Three typical cases are cited
below:
=1. When there is a Generating Plant in the Building, and a Plant Using
1¹⁄₄-in. Hose and 8-in. Vacuum is Desired.=--A Root blower will require
27 watts for each cubic foot of air exhausted (Fig. 88), and the
three-sweeper aspirator, 0.065 lbs. of steam. Then the pounds of steam
required by the aspirator to do the same work as one K. W. hour at the
motor of the Root blower will be
0.065 × 60
---------- = 146.3
0.027
The generating plant will produce a kilowatt hour at the switchboard
with not exceeding 60 lbs. of steam, and if the transmission loss is
10% there will be required by the Root blower not over 66 lbs. of steam
to do the same work that takes 146 lbs. with the aspirator. This case
would require that the Root blower, driven by an electric motor, be
used.
=2. When there is High Pressure Steam Available, but no Generating
Plant.=--Then we may use either the aspirator or a Root blower driven
by a steam engine. This engine should have an economy of 60 lbs. per
indicated horse power, with not over 15% friction loss, which will
require 69 lbs. per brake horse power. This will be equivalent to 69 ×
0.776 = 90¹⁄₂ lbs. per K. W. hour, which is still much better than 146
lbs. required by the aspirator.
=3. When Steam is Generated on the Premises with Coal Costing $3.00
per ton and all Machinery Must be Driven by Electricity Purchased for
5 Cents per K. W. Hour.=--Cost of steam to do the same work in the
aspirator that 1 K. W. hour will do in a motor driving a Root blower is:
146 × 300
--------- = 2.8 cents
7 × 2240
as against 5 cents that would have to be paid for current. In this case
there would be a saving in using the aspirator, which would not require
as much attention as the motor, and at loads less than full load, the
steam used by the aspirator would be in direct proportion to the load,
as the control would shut the steam off entirely during a portion of
the time, while the motor would require some current as long as it was
in operation, even if no air was being exhausted. On the other hand,
the steam which is exhausted from the aspirator is not suitable for use
in heating, as it is mixed with air and fine dirt, and must be thrown
away, a condition that must always be considered where there is an
opportunity to use exhaust steam for heating or other purposes.
CHAPTER X.
CONTROL.
When the displacement type of vacuum producer of more than one-sweeper
capacity is used with a vacuum cleaning system, some means must
be employed to prevent the vacuum rising above that necessary for
efficient operation of the sweepers when there are less renovators in
use than the capacity of the vacuum producer or when carpet renovators
are in use on all outlets.
If the displacement pump be run at constant speed, every change in the
quantity of air exhausted will cause a change in the vacuum produced.
This will result in inefficient operation and may result in undue
effort being necessary to operate the renovator and in excessive wear
on the carpets.
The earlier systems were not provided with any control and the first
attempt to control the vacuum was by placing a spring relief valve on
the pipe line near the separator, which admitted additional air when
the vacuum tended to rise. This resulted in full load being thrown on
the pump at all times when the same was in use, which does not give
economical operation.
The controllers that have been devised for maintaining a constant
vacuum without the introduction of air into the system operate on one
of three principles:
1. Closing the suction of the vacuum producer.
2. Opening the suction of the vacuum producer and holding vacuum in the
system.
3. Varying the speed of the vacuum producer.
[Illustration: FIG. 99. FIRST TYPE OF CONTROLLER INTRODUCED BY THE
SANITARY DEVICES MANUFACTURING COMPANY, KNOWN AS THE “UNLOADING VALVE.”]
The first type of controller was introduced in the vacuum cleaning
field by the Sanitary Devices Manufacturing Company, and was known as
the “unloading valve.” It was similar to the unloader which had been
used for some time in connection with air compressors. The detail of
construction is shown in Fig. 99, and consists of a balanced valve,
which is connected to a weighted piston, operating in a chamber
communicating with the separators by a pilot valve. The pilot valve
is operated by an auxiliary piston which is weighted to overcome the
lifting effort due to the vacuum desired. When the vacuum in the
cylinder becomes great enough to overcome the weights attached to the
auxiliary piston, it rises, allowing vacuum to reach the main piston,
which is drawn up and the suction valve closed. When this valve is
closed the vacuum in the pump at once starts to build up to the maximum
possible for the pump to produce, and if the pump used is of the piston
type the vacuum will run up to nearly 28 in., resulting in the pump’s
taking the least power on which it can be operated. As soon as the
vacuum in the separators falls below that which will sustain the weight
on the auxiliary piston the valve falls open and the pump again draws
air through the system. In actual practice this valve will operate at
more or less frequent intervals. The author timed the action of one of
these valves connected to the suction of an eight-sweeper piston pump,
and its time varied from ²⁄₅ second to 65 seconds. The current taken
by the pump when the suction was open was 100 amperes at 220 volts.
When the valve was closed for but ²⁄₅ second the current dropped to
75 amperes, there not being sufficient elapsed time for the pump to
produce a perfect vacuum. When the valve was closed for 2¹⁄₅ seconds,
the vacuum reached its maximum value and the current fell to 32 amperes.
Fig. 100 is a curve plotted from the results of this test and shows an
increase in the power above that necessary to overcome the friction in
the moving parts of the pump in direct proportion to the percentage of
full load that the pump was serving.
[Illustration: FIG. 100. TEST OF CONTROLLER CONNECTED TO SUCTION OF
8-SWEEPER PISTON PUMP.]
This is as near an ideal condition as one could expect to obtain by any
means other than stopping the pump or otherwise decreasing the friction
load. However, this form of unloader is not suitable for a pump without
valves, as the power will increase with an increase in vacuum, and
other means must be employed to control such a pump.
The second form of control is adapted to this type of pump. The
arrangement of one of these controls is shown in Fig. 101. This
consists of a single-ported valve opened by the vacuum in the cylinder,
M, the action of which is controlled by a pilot or auxiliary control
valve actuated by the vacuum in the separator. This auxiliary valve is
fitted with two pistons, S and O, which are held together by springs,
and when so held the main cylinder is open to the atmosphere through
the small ports in the piston, O. When the vacuum in the separator
becomes great enough to overcome the compressive strength of the
springs, T and P, the pistons, S and O, are drawn apart, closing the
port in the piston, O, and opening the port in piston, S, allowing the
vacuum to enter the main cylinder, M, and open the main valve. This
valve permits the atmospheric pressure to enter the pump suction, the
air being prevented from entering the separators by a check valve, not
shown. The pump then operates without producing any vacuum, and the
power required to operate the pump is reduced. A relief valve of the
common vacuum-breaker type is shown at the left of the cut. This valve
is provided to prevent overload in case the control fails to operate.
[Illustration: FIG. 101. TYPE OF CONTROLLER FOR USE ON PUMPS WITHOUT
VALVES.]
This type of control does not effect as great a reduction in the power
as the first type of control described, since it requires a greater
per cent. of the full load power to operate the pump at no vacuum than
at perfect vacuum. No air is moved in the latter case, and the maximum
volume of air is moved in the former case.
Either of these controls gives fairly economical results when the pump
is serving at least a part of the sweepers at all times. However, when
the system is used in a building where there may be cleaning done at
any time and vacuum must be “on tap” at all times, as in a hotel, there
will be many occasions when no sweepers will be in use, and the pump
might then be stopped entirely, provided that it could be automatically
started when needed.
[Illustration: FIG. 102. REGULATOR FOR MOTOR-DRIVEN VACUUM PUMP,
MANUFACTURED BY THE CUTLER-HAMMER MANUFACTURING CO.]
Where the steam aspirator is used, the control (Fig. 97) is attached to
the steam supply valve. When the valve is closed no steam is consumed
by the aspirator. This is the ideal condition where we must keep vacuum
“on tap,” and is a characteristic of the aspirator system which has led
to its introduction in many instances.
The same economy can be obtained with a steam-driven pump by inserting
a throttle valve, controlled by the vacuum in the separators, which
will start and stop the engine driving the pump and vary its speed in
accordance with the quantity of air required by the system.
Several appliances for varying the speed of a motor-driven vacuum
pump have been placed on the market, the simplest and probably the
best of these appliances being that manufactured by the Cutler Hammer
Manufacturing Company, illustrated in Figs. 102 and 103.
[Illustration: FIG. 103. INSPIRATOR TYPE VACUUM CONTACTOR, USED TO
CONTROL PILOT MOTOR OF CUTLER-HAMMER CONTROLLER.]
The object of the apparatus shown in Fig. 102 is to automatically
start a motor-driven vacuum pump and control the speed of the motor
so that the vacuum is maintained at the desired degree, irrespective
of variation in the number of sweepers in use. This control of the
degree of variation is accomplished in a more efficient manner than if
the pump were to be driven at its maximum speed at all times and the
pressure kept at the desired point by means of a blow-off or by-pass
valve. With this system a motor is used having a control, by shunt
field weakening, of approximately 3:1 in order that the control of the
speed may be as efficient as possible.
Referring to Fig. 103, a small pilot motor is mounted on brackets
at the side of the panel, driving directly, through an insulating
coupling, a screw shaft which carries a traveling cross-head. This
cross-head is shown in the photograph at the extreme right of its
travel, which corresponds to the maximum speed of the motor, the
left-hand end corresponding to zero speed of the motor. In this
position the motor circuit is opened by the clapper type magnetic
switch. Assuming that the cross-head is in the extreme left-hand
position and the knife switch is closed, the pilot motor will be
started in such a direction as to move the cross-head to the right.
A slight movement in this direction completes a connection to the
magnetic switch, which thereupon closes the motor circuit through all
of the resistance, starting the pump motor.
Inasmuch as the pilot continues to move the cross-head toward the
right, the speed of the pump will be gradually increased until, at a
point about midway of its travel, all of the resistance in the armature
circuit of the motor will have been cut out upon the upper segments and
further movement then serves to weaken the field. This is accomplished
by means of the contact buttons shown just below the screw shaft.
As soon as the cross-head has weakened the field to its minimum
value and thus speeded the motor up to its maximum point, a limit
switch stops the pilot motor and thus prevents further motion in that
direction. As soon as the pump working this at its maximum speed has
produced a vacuum in the cleaning system of, say, 12 in. of mercury,
the cross-head will begin to move backward and reduce the speed to a
point corresponding with the air required.
This control of the pilot motor is accomplished by means of what is
termed “inspirator type vacuum contactor.” This apparatus is shown more
in detail in Fig. 103, and consists of a diaphragm closing one side of
a chamber. The diaphragm is pressed outward by an internal spring whose
tension may be adjusted by means of a hexagonal head cap screw, visible
in the photograph of the complete regulator.
The diaphragm is coupled to a pivoted arm carrying insulated
conical-pointed silver screws, so located that they enter holes in
small silver plates mounted on opposite sides, respectively, of the
upper and lower contact posts. These contact posts are hollow and
communicate with the diaphragm chamber, which latter is connected by
piping to the vacuum system.
Normally, the internal spring forces the diaphragm over so that the
lever makes contact with the lower post. This serves to drive the pilot
motor in a direction to move the cross-head to increase the speed of
the pump. When the degree of vacuum for which the apparatus is adjusted
is reached the lever starts to move toward the left hand, and in so
doing stops the pilot motor. This maintains the pump speed at that
particular value. Should the vacuum increase to a sufficient degree the
lever will be drawn further over toward the left and contact will then
be established with the upper post, which will cause the pilot motor to
move the cross-head to the left, and thus decrease the pump motor speed.
Inasmuch as the motion of the diaphragm lever is very gradual,
destructive arcing would take place at the pilot motor contacts were
it not for the small openings in the silver contact plates, which, as
the pointed screw leaves the hole, immediately sucks the arc inward and
extinguishes it.
This method of preventing arcing is exceedingly unique and is subject
to patents now pending.
It is possible to adjust the high and low limits by changing the
setting of the pointed silver screws, the usual adjustments being such
as to maintain the vacuum within 2 in. of mercury. The speed of the
pilot motor may be adjusted by means of the small link shown in the
upper left-hand corner of the panels to correspond with the capacity
of the system, it being found that systems of large capacity require a
slower motion than those in which the amount of piping, etc., is less
for the same size of pump. In practice, the regulator will very quickly
find the position corresponding to the proper speed for the number of
outlets in use, and only moves a slight amount either side of this
particular position.
With this regulator it is possible to employ remote control permitting
the establishment of vacuum in the piping system by the turning of a
pilot switch located at any point in the building. If desired, several
such switches may be placed in parallel, and, under these conditions,
the turning on of any switch will establish the vacuum supply which
will be maintained until all of the pilot switches are turned off. By
this means it is possible to have several janitors working at the same
time on different floors of the building, and each will be independent
of the others in his control of the vacuum; although one man may finish
and turn off the switch on his floor, the pump will not be stopped if
the vacuum is still required by workers on other floors.
When the total size of one installation becomes greater than 25 H. P.,
it is found desirable to provide two pumping units, and, in this case,
the same system is applicable. The cross-head is then arranged to start
first one pump and increase its speed to a maximum. If this does not
supply the necessary amount of air, the cross-head continues to move,
and starts the second pump, which will then be run at a necessary speed
to supply the remaining amount of air.
The first pump always remains in motion at its point of highest
efficiency. It is evident that this duplex arrangement is more
efficient than one large pump when only a very few sweepers are in
operation, since, for this condition, the very large pump would have
to be run at such a slow speed that the armature resistance would be
in circuit, while the single smaller pump would be running at a more
efficient speed and with less proportionate motor losses.
In duplex outfits switches are provided for disconnecting either motor
in case of its being necessary to clean or repair either unit. When
so disconnected the other unit may be operated and maintain the same
degree of vacuum within the limits of its capacity.
While this type of control is more economical in current consumption
than either of the former types described, its cost is much higher, and
it is seldom used unless specifically ordered.
When the centrifugal type of vacuum producers is used no control is
necessary, as the inherent feature of this type of apparatus insures a
practically constant vacuum at all air quantities within the capacity
of the machine.
CHAPTER XI.
SCRUBBING SYSTEMS.
Vacuum cleaning systems in which appliances for scrubbing are provided
in addition to the usual appliances for the removal of the dust
and other materials in a dry state have been introduced by a few
manufacturers, none of which has come into general use.
The usual method employed is to provide an ordinary corn scrubbing
brush which has a connection to the water supply of the building, with
control valves in the tool handle for regulating the flow of water to
the brush. Soap is applied either in the form of soap powder sprinkled
on the floor, in a liquid state fed into the water supply by means of a
sight-feed oil cup or soft soap in a plastic state fed into the water
supply by means of a compression grease cup.
In any case, the water is run onto the floor mixed with the soap and
the floor scrubbed by manipulating the corn brush, in the same manner
that an ordinary corn scrubbing brush without attachments would be used.
After the dirt has been loosened from the floor, the floor may be
rinsed by the application of more water. The water is then drawn up
from the floor by the suction of the cleaning machine, and passes
through the hose and piping system to the separator and vacuum
producer. To effectively remove the water a rubber-faced tool is
usually employed. In one system this rubber face is arranged to permit
the corn brush to be fitted over same when scrubbing is being done, and
the brush must be removed from the tool before the water can be drawn
up from the floor. Other manufacturers provide a double-faced tool
having the brush on the opposite side of the tool from the rubber-faced
slot. By reversing the tool, scrubbing and mopping can be accomplished
without the removal of the corn brush from the tool, which is more
convenient for the operator.
With either of the above forms of scrubbing tools it is necessary or
desirable to cut off the suction to the mopping attachment when using
the corn brush, and it is also necessary to cut off the water supply
to the brush when using the mopping attachment. One system, introduced
several years ago, conducted the water to the brush and away from the
rubber-faced mopping appliance through the same hose. This arrangement
requires the use of a special three-way hose cock, which had to be
manipulated frequently during the scrubbing operation, requiring the
time of another person in addition to the operator, or else greatly
delaying the scrubbing process by requiring the operator to constantly
pass back and forth between the hose cock and the scrubbing tool. This
method of supplying water also requires the use of a removable corn
brush attached over the rubber mopping device.
Other forms of scrubbing appliances are provided with separate hose
for the water supply and suction and with valves in the handles for
controlling the suction and water supply. These valves to be efficient
and quick in action are generally made self-closing, otherwise they
will be short-lived, as explained in Chapter V. When springs are used
to close the valves, the hand and wrist will be quickly fatigued, as
stated in Chapter V.
With either of the above systems all of the scrubbing, that is, the
agitation of the brush, has to be performed by the operator, as in the
case of the ordinary scrubbing brush. However, the combination tool is
much heavier and clumsier than the ordinary scrubbing brush, and the
only advantage obtained by using this heavy and clumsy appliance is
the ability to supply water without carrying it in buckets, also the
removal of the dirty water after scrubbing. These appliances cannot be
termed mechanical scrubbers, nor can they be classed with scrubbing
machines with motor-driven brushes, such as have been recently
introduced.
A real mechanical scrubbing device for use with a vacuum cleaning
system was manufactured by Foster & Glidden, of Buffalo, N. Y., but
was never placed on the market, although at least one is in commercial
operation to-day. This machine is provided with a turbine motor
operated by the air current passing through the machine. This turbine
revolves a pair of scrubbing brushes turning in opposite directions.
Water is fed through a separate hose, and an auxiliary air inlet is
opened when the suction under the brushes is closed, in order to supply
the necessary air to keep the turbine running. Mr. Foster states that
he has experienced no trouble in operating this machine on from 8 in.
to 12 in. of vacuum, being able to scrub and remove the dirt and water
with one operation. The speed with which the work was done depended on
the condition of the floor, the usual rate, as given by Mr. Foster,
being from 10 to 12 yds. per minute.
Mr. Foster also states that he has not pushed the introduction of this
scrubber, as he considers it so far ahead of the times as to require
the education of the public in the use of the hose and ordinary vacuum
cleaning tools before users would be capable of successfully operating
this type of scrubber.
The author considers this condition to be lamentable if true, for until
some such appliance is in commercial use scrubbing attachments to a
vacuum cleaning system can never compete with the mechanical scrubbing
machines now on the market, and are little if any better than the old
method of scrub-brush, mop and pail, and certainly not as rapid in
operation.
When the vacuum cleaning systems combine scrubbing with dry cleaning,
the separator and vacuum producer must provide for the removal of
water as well as air. A few manufacturers have attempted this, among
which are the makers of the Rotrex system, described in Chapter IX, in
which the water is passed through the pump and into the sewer under
sufficient pressure to overcome the friction in the exhaust pipe
through which the expelled air passes after leaving the separator. This
may be sufficient to force the trap seals of the plumbing system, and,
if used, the discharge connection should be made to the sewer outside
the main running trap, close to the fresh air inlet. As large articles
cannot be allowed to pass through the pump, a screen is necessary on
the inlet side of the vacuum producer, but this may give trouble, due
to the clogging with litter.
The Atwood Vacuum Cleaner Company uses a wet tank on the suction side
of the vacuum producer into which the dirt and water are discharged,
the air being separated and passed to the vacuum producer. When this
tank becomes partly filled it is necessary to shut down the plant and
empty the contents of the tank by gravity into the sewer.
This method overcomes the objections to clogged screens and forced
trap seals, and all litter is discharged direct to the sewer, together
with a quantity of water which is presumably sufficient to flush the
litter through the sewer. The last named system is still open to
two objections; first, it is not automatic, and, if neglected, the
tank will fill with water and force same into the vacuum producer.
With the Root type of vacuum pump this will do little harm unless a
large quantity of floating litter should pass into the pump. Second,
the system may be operated with dry renovators exclusively for a
considerable portion of the time, in which case the contents of the
separator may become of such a consistency as will not readily flush
through the sewer, and stoppage of the same may occur.
Another separator of this type has recently been patented by E. B.
Dunn, the originator of the Dunn Locke, in which the mud and the water
are automatically discharged alternately from one of two separators, as
described in Chapter VIII.
Such a separator, in which sufficient water is automatically introduced
to dilute the dirt and which will automatically empty when sufficiently
filled, when so constructed that it will operate continuously,
is considered to be the ideal separator for use with a combined
cleaning and scrubbing system. Until the mechanical scrubber and an
automatically operated separator are commercially introduced the author
does not consider that the use of scrubbing attachments, in connection
with the vacuum cleaning system, is advisable.
CHAPTER XII.
SELECTION OF CLEANING PLANT.
We have considered in detail the various appliances which, taken
together, make a complete vacuum cleaning system, but without
considering their relation to one another. It now becomes necessary to
choose an exact type and form of each of these appliances which will
produce in combination a complete vacuum cleaning system best suited to
the conditions to be met in a given installation.
In selecting a vacuum cleaning system consideration must be given to
the character of the material to be removed, the kind and quality of
the surfaces to be cleaned, the rate at which cleaning must be done,
the extent of the cleaning system, and the cost of labor to operate the
system, all of which must be considered in each step in the selection
of a suitable plant.
In assembling the complete system, the author will take up the various
parts thereof in the order in which they were discussed in the
preceding chapters.
=Renovators.=--The selection of renovators is the most important step
in making up a vacuum cleaning system, as the entire makeup of the
system, whether good or bad, is dependent on the proper selection of
these tools. The carpet renovator is generally considered first in
importance, because the cleaning of carpets has nearly always been
found to be the principal field of usefulness in vacuum cleaning work.
This is due, perhaps, largely to the fact that from the beginning of
the art of vacuum cleaning, this function of the system has been held
before the eyes of the public by the manufacturers of the earlier
systems. Nearly all demonstrations of cleaning systems shown to the
public consist of the removal of ordinary wheat flour from a carpet.
The reason for this is two-fold; first, because it is the most striking
demonstration to the eye of the layman, and, second, it is the easiest
to accomplish with a small air displacement and small power, which was
characteristic of the apparatus made by these manufacturers.
The author was at one time of the opinion that this function of the
cleaning plant was given too much prominence by builders of systems
having small air displacement, and letters were sent to the officials
in charge of sixteen Government buildings in which vacuum cleaning
systems were installed, asking them, among other questions, whether
the cleaning system was used to any extent in cleaning bare floors, of
which there were large areas, both wood and marble, in the buildings
in question. The plants installed were of various makes, some of
which maintained 12 in. mercury at the separator and used 1-in. hose,
while about an equal number of others maintained 6 in. mercury at the
separator and used 1¹⁄₂-in. hose. The answers showed that out of the
sixteen buildings the cleaner was used on bare floors in but two of
the buildings. One writer, who had a plant maintaining 6-in. vacuum,
provided with Type F renovators and 1¹⁄₂-in. hose, stated that he
had tried cleaning bare floors without success, as the renovator and
hose became so clogged with litter as to be inoperative. The majority
stated that the cleaning system displaced brooms on carpets and rugs
and several stated that the cleaning system was used to advantage in
cleaning walls, cases, pigeon holes and relief work.
This indicates that for the average office and departmental building
the cleaning of carpets is the most important function of the vacuum
cleaner. This is also true of residence work. Schools, department
stores and manufacturing buildings contain very little floor space
covered with carpets, and in buildings of this character the cleaning
of bare floors is of the greatest importance. In such cases the
efficiency of the carpet renovator can be sacrificed to a more
efficient and economical operation of bare floor renovators.
In a building where carpet cleaning is an important function of
the cleaning system, the selection of the carpet renovator is most
important. Of all the various types of carpet renovators discussed in
Chapter III, only two need to be considered, Type A and Type F. Of
these, Type A is superior in all respects except the picking up of
large litter, and, unless the character of the material to be removed
contains a large amount of material which can be picked up by Type F
renovator that will not pass Type A, Type A renovator should always be
used. Even when Type F renovators are desirable, the writer considers
that the plant should still contain some Type A renovators for use in
places where this unusual litter will not be encountered.
Among the bare floor renovators, described in Chapter IV, only the one
having a felt face, curved to permit its running over the dirt, is
worthy of serious consideration. This renovator requires an inlet or
vacuum breaker to keep same from sticking to the surface cleaned, the
extent of such opening being dependent on the vacuum maintained in the
carpet renovators, as explained in Chapter VII.
When carpet cleaning is considered as of secondary importance to bare
floor cleaning, the degree of vacuum maintained at the separators
may be reduced to that which will produce a vacuum of 1 in. mercury
at the bare floor renovator, allowing the vacuum maintained at the
carpet renovator to be whatever the conditions of hose and pipe line
will produce. Under such conditions, the area of the inrush or vacuum
breaker in the bare floor renovator may be reduced considerably.
The use of brush renovators is dependent on the capacity of the air
exhauster supplied, as explained in Chapter VI. If it is decided that
brush renovators are necessary, then the “large volume” exhauster must
be installed. The advisability of such installation is dependent on the
time allowed for cleaning and the cost of the operators. In residences
and small buildings where the cleaning operations can be done with one
or even two domestics or laborers, very little, if any, saving in the
wages of operators can be effected by increasing the rate at which the
cleaning can be done. In such buildings a small-volume plant will be
the most economical in first cost and operation. If such a plant is
installed, the brush renovators should be omitted.
In cases where bare floor cleaning is the principal function of the
cleaning system the extra quantity of air at the low vacuum necessary
will not require much larger expenditure of power than that needed
by the small-volume plants when maintaining sufficient vacuum for
effective carpet cleaning and brush renovators should be provided with
systems of this character.
=Hose.=--In Chapter VI it is shown that when carpet renovators are
operated efficiently in combination with bare floor renovators,
1¹⁄₄-in. hose will produce the best results with the lowest expenditure
of power at the hose cock. In Chapter VII it is shown that with pipe
lines of ordinary length 1¹⁄₄-in. hose also gives the best results,
with the least expenditure of power at the separator, but that in cases
of exceedingly long pipe lines, 1-in. hose will be the most economical.
In a system where bare floor cleaning is the principal function,
the vacuum to be maintained at the carpet renovator is no longer
considered, and for such systems the largest hose which can easily
be handled will cause the least hose friction and require the lowest
vacuum at the hose cock. It is, therefore, the most economical to use
on such a system. The author does not recommend the use of a hose
larger than 1-³⁄₄-in. diameter for this type of plant.
The proper hose sizes, therefore, will be: For ordinary buildings where
carpet cleaning is important, 1¹⁄₄-in. diameter. For installations with
unusually long lines of piping, where carpet cleaning is important,
1-in. diameter.
For all systems where carpet cleaning is of secondary importance,
1¹⁄₂-in. or 1-³⁄₄-in. diameter.
=Pipe Lines.=--Pipe lines should always be as large as possible without
reducing the velocity in same below 40 ft. per second, as explained in
Chapter VII.
=Separators.=--The type of separator to be used is dependent on the
type of vacuum producer adopted. Where reciprocating exhausters are
used, or other type of exhauster where there is rubbing contact between
the moving parts and the dust, the combination of a wet and dry
separator is recommended. When rotary or centrifugal exhausters having
close clearances are used, total separators with bags are recommended.
When exhausters with large clearances are operated, partial separators
are satisfactory.
The use of any form of apparatus contemplating the adoption of a
satisfactory scrubbing system is not considered advisable, as the
author believes that separators for handling water will be improved
before scrubbing becomes commercially successful. Changes in the
existing separators can be made when satisfactory scrubbing appliances
are placed on the market, at no greater expense than would be necessary
to bring up to date any of the present systems for handling water.
=Vacuum Producers.=--The selection of the vacuum producer is dependent
on the degree of vacuum that must be maintained to effectively operate
the system selected. For the operation of a system where carpet
cleaning is the principal function and 1¹⁄₄-in. hose is used, the
vacuum required at the producer will be from 6 in. to 9 in. mercury.
Inspection of the efficiency curves of the various types of vacuum
producers, given in Chapter IX, shows that the two-impeller rotary pump
has the highest efficiency at this vacuum.
For the operation of systems where carpet cleaning is the most
important function and 1-in. hose is found to be the most economical,
14 in. to 15 in. of vacuum at the vacuum producer is necessary, and
efficiency curves, given in Chapter IX, show that the piston pump is
the best suited for such service.
For the operation of a system where carpet cleaning is of secondary
importance a vacuum at the producer of from 2 in. to 4 in. of mercury
will be sufficient. For this work, the multi-stage or even single-stage
centrifugal fan is practically as efficient as the two-impeller rotary,
and will be lower in first cost and cost of maintenance. Either of
the above mentioned vacuum producers are satisfactory for operating a
system of this type.
=Control.=--Every system of more than one-sweeper capacity in which a
displacement type of exhauster is used should be provided with some
means of economically controlling the vacuum at the producer. On
one-sweeper plants an automatic starter which will stop the motor when
the vacuum reaches a point 2 in. above that required and start same
when the vacuum drops to 1 in. below that required is convenient, but
not necessary.
For piston pumps and all other displacement pumps fitted with
eduction valves, an unloading device, which closes the suction when
the necessary vacuum is exceeded, is the least expensive to install
and gives very good economy when the demand on the plant is fairly
continuous during the time it is in operation. Where the service is
intermittent and required at nearly all hours, the Cutler Hammer
control, described in Chapter X, is the most economical.
With displacement exhausters having no eduction valves, the by-pass
type of control is satisfactory where the service is continuous, but
is not as economical, as the unloader used with producers having
eduction valves and the Cutler Hammer control is more efficient under
all conditions of service. Centrifugal exhausters need no control, as
vacuum control is an inherent feature of these machines.
Summing up the subject, we can divide the vacuum cleaning systems
into four classes, each of which requires a different selection of
appliances. They are as follows:
=Class 1.=--Plant for residence or small office or departmental
building, to be not more than one-sweeper capacity.
Renovators: See list given for “small volume” plant, Chapter IV.
Hose: 1¹⁄₄-in. diameter.
Separator: Centrifugal, dry, with bag or screen.
Vacuum Producer: Two impeller, rotary, alternate centrifugal fan.
Capacity, 30 cu. ft. of free air per minute, 4 in. vacuum at producer.
Control: Automatic starter, operated by vacuum.
Size of motor: ¹⁄₂ to 1 H. P.
=Class 2.=--Large office or departmental building where carpet cleaning
is important and pipe lines are of reasonable length.
Renovators: See list given for “large volume” plant, Chapter IV.
Hose: 1¹⁄₄-in. diameter.
Separator: Centrifugal, dry, with bag or screen.
Vacuum Producer: Two impeller, rotary. Capacity, 70 cu. ft. of free air
per minute for each sweeper of plant capacity at 7 in. to 9 in. vacuum.
Size of motor: 2¹⁄₂ H. P. per sweeper capacity.
Control: Cutler Hammer.
=Class 3.=--Large building or group of buildings where carpet cleaning
is important and long lines of piping are necessary.
Renovator: See list for “large volume” plants, Chapter IV.
Hose: 1-in. diameter.
Separators: One centrifugal dry and one wet.
Vacuum Producer: Piston type pump. Capacity, 45 cu. ft. of free air per
minute for each sweeper of plant capacity at 14 in. vacuum.
Size of motor: 4 H. P. for each sweeper of plant capacity.
Control: Automatic unloader for continuous service. Cutler Hammer for
intermittent work at all times.