This class of pumps differs from the centrifugal pump, which is
described and illustrated hereafter, in that it includes a _revolving
piston_, while in the centrifugal pump there is a set of _revolving
blades_ which acts upon the liquid in the same way as a fan acts upon
the air; _the centrifugal pump receives the water in the center and
throws it outward, while the rotary gathers the fluid up and leads it
towards a central discharge_.
The rotary pump substantially corresponds to the pressure blower,
and in many cases is simply the rotary engine reversed; while the
centrifugal pump is analogous to the fan-blower. The functions of a
rotary are almost identical with those of piston and power plunger
pumps.
_The rotary pump on account of its cleanliness_ has been quite
generally adopted for pumping all heavy liquids, such as starch, paint,
soap, gummy oils, beer and hops, sewerage, bleachers, etc.
The rotary pump is used also in places where a piston or steam pump
would be objectionable either on account of floor space occupied or for
the reason that steam could not be had without too much expense for
lifting and forcing water and other liquids which would not nor could
not find their way through the tortuous and narrow passages of the
average piston and plunger pumps.
_For low heads of liquids_ the rotary is also somewhat more efficient
than direct acting pumps and the absence of close fitting parts
renders it possible to handle water containing a considerable
quantity of impurities, such as silt, grain and gravel. This type of
pump is compact and is generally self-contained, especially in the
smaller sizes, and will deliver more water for a given weight and
space occupied than the reciprocating types, while its simplicity of
construction not only lessens the liability to derangement, but enables
persons having a limited knowledge of machinery to set up and operate
these pumps successfully.
Rotary pumps are driven by means of belts from line shafting and by
wheel gearing, and also by direct connection to any prime mover such as
a steam or gas engine, hydraulic or electric motor.
_Rotary pumps may be divided into several classes_ according to the
forms of, and methods of working the pistons or impellers, as they are
usually called, that is, according to the construction and arrangement
of the abutments. The abutment receives the force of the water when
driven forward by the pistons or impellers and also prevents the water
from being carried around the cylinder, thus compelling it to enter the
delivery pipe. _In the construction of the impellers or pistons, and
of the abutments, lie the principal differences in rotary pumps._ In
some pumps the abutments are movable, and are arranged to draw back, as
shown in Fig. 469, to allow the piston to pass. In others the pistons
give way when passing fixed abutments, and in others the pistons are
fitted with a movable wing, as in Fig. 472, which slides radially in
and out when passing the abutment.
[Illustration: FIG. 469.]
Pumps of this type having no packing and springs to prevent leakage and
in which the pistons work in cylindrical casings or cylinders are quite
durable and in many instances have been known to run for months without
stopping. The later construction of this pump is shown in Fig. 470;
this design of pump is more economical, as a rule, owing to the fact
that the strain on the belt is uniform at all points in the revolution
of the pistons.
Fig. 467, page 194, represents one of the oldest and most efficient
forms of the rotary pump. Cog wheels, the teeth of which are fitted to
work accurately into each other, are inclosed in an elliptical case.
The sides of these wheels turn close to those of the case so that water
cannot enter between them. The axle of one of the wheels is continued
through one end of the case (which is removed in the figure to show
the interior) and the opening made tight by a stuffing-box or collar
of leather. A crank is applied at the end to turn it, and as one wheel
revolves it necessarily turns the other, the direction of their motions
being indicated by the arrows. The water that enters the lower part
of the case is swept up by the ends of each cog in rotation; and as
it cannot return between the wheels in consequence of the cogs being
always in contact there, it must necessarily rise in the ascending or
forcing pipe.
Fig. 468 represents a pump similarly constructed to the foregoing, _but
having cams_ shaped so as to reduce the wear.
[Illustration: FIG. 470.]
_In Eve’s pump_, shown in Fig. 469, a solid or hollow drum, _A_,
revolves in a cylindrical case. On the drum are three projecting
pieces, which fit close to the inner periphery of the case. The surface
of the drum revolves in contact with that of a smaller cylinder, _B_,
from which a portion is cut off to form a groove or recess sufficiently
deep to receive within it each piston as it moves past. The diameter
of the small cylinder is just one-third that of the drum. The axles
of both are continued through one or both ends of the case, and the
openings made tight with stuffing-boxes. On one end of each axle is
fixed a toothed wheel of the same diameter as its respective cylinder;
and these are so geared into one another, that when the crank attached
to the drum-axle is turned (in the direction of the arrow) the groove
in the small cylinder receives successively each piston, thus affording
room for its passage, and at the same time, by the contact of the edge
of the piston with its curved part, preventing water from passing. As
the machine is worked, the water that enters the lower part of the pump
through the suction-pipe is forced round and compelled to rise in the
discharging one, as indicated by the arrows. Other pumps of the same
class have a portion of the small cylinder cut off, so that the concave
surface of the remainder forms a continuation of the case in front
of the recess while the pistons are passing; and then, by a similar
movement to that in the figure described, the convex part is brought in
contact with the periphery of the drum until the return of the piston.
NOTE.—In the year 1825, one Mr. J. Eve, an American, took out a
patent in England which was practically the beginning of the modern
era of rotary engines and pumps. His pump consisted chiefly of a
revolving cylinder having three teeth or projections and revolved
within a case. A second and smaller cylinder was also placed within
this case. The smaller cylinder had one side scooped out to permit
each of the teeth upon the large cylinder to pass as they came
opposite the small cylinder. The two shafts being geared together the
small cylinder was caused to revolve three times to one of the large
so that the teeth might pass the small cylinder without interruption.
[Illustration: FIGS. 471 AND 472.]
The next improvement in rotary pumps is shown in Fig. 470, page 197.
This type was used for many years as a fire pump. The Silsby fire
engine of the present day is practically this pump in design although
it has packing strips in the center of each of the long teeth of the
elliptical gears.
Following Eve’s invention were a series of claims which embodied the
design shown in the engraving, see Fig. 471, where a sliding partition
or abutment, A, was used to imprison the steam. As the piston or inside
cylinder turned around, the abutment was pushed up and fell of its
own gravity. A strip of metal supported this abutment and furnished
a suitable wearing surface upon the surface of a revolving cylinder
and also accommodated itself to the tilting motion introduced by the
eccentricity of the revolving cylinder.
In Fig. 472 the sliding abutment has been placed in the side of
revolving cylinders and the axis of this cylinder is in its center. In
this case the abutment is pushed in by its pressure upon the inside of
the case and is thrown out by its centrifugal force assisted by spiral
springs.
The engraving, Fig. 468, gives a view of _Gould’s rotary pump_, with
the case removed; long practical experience has demonstrated that the
revolving cams or pistons are of such a shape as to produce the minimum
of friction and wear with the greatest results.
The cases which receive these cams are engine lathe turned and bored
and so true and smooth that the cams when in operation create almost a
perfect vacuum and will “pick up” water for a long distance and hold it
efficiently. The cams are carefully and accurately planed to mesh into
each other to fit their case.
It is a point worth noting that if a little good oil be put into the
case of these pumps before and after using at first, or simply to pump
air with the oil a few times, the cams become as hard upon the surface
as tempered steel, and are almost unaffected by long use afterwards.
Drip plugs are provided for draining pumps in cold weather. To do this,
turn the cams backward a single revolution to release all water.
_The Taber pump_ is one of the best known of the rotary class. It
consists of three parts only, that is to say, (1) the outside shell or
case, (2) the piston, and (3) the valves.
Referring to the engravings herewith (Figs. 474 to 481), the outside
case or shell, A, is made either of brass or iron as the case may be,
Fig. 476, bored out at F to receive the piston, C, Fig. 478, to which
power is applied at G.
[Illustration: FIG. 474.]
This cylinder has two heads or covers, BB, Figs. 475 and 477, which
close the cylinder and has journal bearings to carry the piston
combined with packing boxes to prevent leakage of the liquid passing
through the pump. The valves, Figs. 479, 480 and 481, DDD, are plates
of composition which slip through the piston fitting neatly into the
slots, EE, Fig. 478.
[Illustration: FIGS. 475-477.]
[Illustration: FIG. 478.]
[Illustration: FIGS. 479-481.]
These valves really perform the work of pumping. It will be observed
that substances which would easily clog up an ordinary pump with clack
valves, will pass through this pump without difficulty; there are no
springs in this pump, nor will it get out of order with the average
treatment, and it pumps all kinds of liquids, either thick or thin,
such as are found between the two extremes of water, and _brewers’
grains_.
It is designed to handle a large amount of fluids and semi-fluids under
a medium pressure, and being well balanced it may be run fast or slow
as desired.
_Directions for setting and operating Taber pumps._
1st. Bolt pump firmly to the floor, and if possible set it so that the
liquid runs into it, which will add very much to the life and duty of
the pump.
2nd. See that all parts are well oiled.
3rd. Experience has proved that common candle wick soaked in tallow is
the best material with which to pack rotary pumps. The wick should be
double and twisted into a compact rope and driven into the boxes as
tightly as possible with a piece of hard wood tapered to fit the box.
Such a tool as described is furnished with each pump. Do not under any
circumstances use iron calking tools which mar the bearing and causes
them to quickly cut out the packing.
4th. If from any cause the pump should become clogged, do not use a
lever in starting it. Remove the plug from bottom and work the pulley
back and forth till the pump is relieved. If this does not free it,
remove the outside head and all parts will be accessible.
NOTE.—Many of the modern breweries are built with the hop-jack
situated upon the upper floors of the brewery, to which the beer
and hops mixed are pumped, and the beer allowed to flow directly
to the coolers. This pump has been very successfully installed for
the past five years, pumping in some breweries 90 feet in height
above the pump. The handling of wet brewers’ grains by use of chain
conveyors, which are seldom free from infection and which are a
continual source of annoyance from breakage, is now overcome by this
pump. All styles of these pumps can be washed out clean after use,
thereby overcoming entirely the noxious smell so disagreeable to this
part of the brewery when conveyors are used. There should be a fall
of six to eight feet from the wash-tub into the pump and as nearly
perpendicular as possible. Right angle bends in the discharge pipe
should also be avoided. By using twenty-four-inch bends wet grains at
70% moisture can be pumped without additional water.
When putting heads back on the pump use ordinary _newspaper for
packing, nothing thicker_, as thicker packing destroys the suction.
Prevent all leaks in suction pipe which would impair the vacuum.
The suction should furnish an uninterrupted supply to the pump, to
enable the pump to throw its full capacity. Never use pipes smaller
than the openings in pump.
Open all drips in cold weather to prevent freezing.
All packing boxes should be kept in order and never allowed to leak.
The illustration, Fig. 482, page 204, represents a rotary pump of the
Holyoke pattern to be attached by a clutch to a line shaft—the gears,
as shown, are merely to transmit the power to the impellers. The safety
valve with lever and weight, shown in the cut, are designed to be
attached to the discharge pipe to guard against over pressure, which
might occur through the closing of valves.
Fig. 483 shows an emergency pump of the Holyoke rotary pattern. It
is of the same general design as the one previously alluded to. It
is driven directly from the line shaft by friction gearing instead
of toothed wheels. The hand wheel attached to the end of a screw is
used to press the smaller friction wheel against the larger and thus
transmit the power to drive the pump.
This mechanism is not liable to injury by being thrown instantly into
gear in case of fire, as would be the case if gear wheels were used.
These pumps are largely used in mills located in the Eastern United
States, _as they may be started up in a few moments at full speed_
without slowing down the engine or motor driving the line shaft.
The shaft bearings are all made of large proportions to avoid heating
and excessive wear when suddenly put under full load.
[Illustration: FIG. 482.]
[Illustration: FIG. 483.]
Figs. 484 and 485 are views of a _rotary pump driven by steam_ and
largely used for fire apparatus. These pumps are in general use in
mills and factories, and can be installed wherever the necessary steam
and water supply are available.
The pump is built on a rigid iron base plate, and is furnished with air
chamber, water-pressure gauge, oil feeders and everything necessary to
make it complete and ready for permanent steam and water connections.
The discharge outlets can be adapted for forcing water through either
pipe or hose.
A perspective view of this pump is given in Fig. 484 and a sectional
plan of the same appliance appears in Fig. 485.
Both engine and pump are of the rotary type and the construction of
these parts is precisely as described in connection with its adaptation
to use in the Silsby steam fire engine.
These pumps can be thoroughly drained and, with their interior surface
well coated with oil and No. 2 pure Graphite, they can be “laid up”
indefinitely and with certainty as to their starting promptly when
wanted in an emergency. Water accumulated in the steam pipe will pass
through this cylinder without causing damage, and the free action
of the pump will not be defeated by the “sticking” of valves or the
corrosion of exposed parts.
In the operation of rotary pumps trouble is often experienced through
an improper adjustment of _the ends of the case_. If the case is too
long there will be leaks of water pass the ends of the impellers and on
the other hand if the case is too short the ends of the impellers will
bind and cut, through excessive friction. Hence great care is necessary
in adjusting the ends of the case so that the pump may run freely yet
without leaks. The packing boxes around the shafts must not be screwed
up too tight otherwise the shaft will be injured.
It has been found by costly experience that _for emergency fire pumps
leather belts are unreliable_, hence these two pumps, Figs. 482 and
483, are driven by direct connection with the shaft in the first
instance and through cast iron friction gearing in the second.
[Illustration: FIG. 484.]
[Illustration: FIG. 485.—See page 205.]
[Illustration: FIG. 486.—See page 210.]
The engraving, Fig. 487, shows _Root’s rotary pump_. This has two
impellers which are geared together and each turn at equal speeds
towards one another at the top. The engraving, Fig. 488, also shows
a Root pump with _two impellers each having three wings or lobes_.
The pump proper consists of half circles, _AA_, with air chambers,
_DD_, cast with them, the head plates, _B_, carrying the bearings,
and the revolvers, _CC_, together with shafts, _EE_. The shafts carry
involute gears at each end which keep the lobes of the two impellers
in their relative positions, and rotate them. Either shaft may be made
the driving shaft and to deliver water, as shown by the arrows in the
cross section, the shafts revolve so that the tops move toward one
another.—Same as in the preceding case.
[Illustration: FIG. 487.]
[Illustration: FIG. 488.]
_The action of this pump is as follows_: the suction pipe on starting,
being full of air, the first few revolutions of the pump expel the
air until the required vacuum is formed, which allows atmospheric
pressure to raise water into the pump. It then flows between the case
and the lobes into the space, _F_, and is carried by the impellers
to the discharge edge of the case, point, _G_, where it enters the
discharge pipe. Each succeeding lobe brings up an amount of water
equal to spaces, _FF_, thus delivering the contents of the six at each
revolution. The irregular form of the lobes keeps them in contact at
the center line, thus preventing the return of water into the suction
below.
Heads of water from 10 to 250 feet are successfully handled by this
type of pump, with a slip of from 5 to 15 per cent., according to the
discharge pressure.
The three-lobe impellers provide a double lock against the return of
water between the case and impellers, at the same time allowing a very
free inlet and outlet for the water. The delivery of water from this
pump is smooth and continuous.
The large engraving, Fig. 486, page 208, shows the exterior of this
same pump with journal bearings and gears encased at each end. This
pump may be driven by motor or engine.
_Large rotary pumps for dredging purposes_ with their engine equipment
for _salt water service_, include surface condenser outfits with air
pumps, feed pumps, fire pumps, etc. The dredges _for fresh water_
are very large cross-compound engines, double-acting air pumps
and jet condensers with the usual complement of vertical duplex
feed pumps, fire pumps, etc. The air pumps are of a very novel
arrangement, inasmuch as it is possible by the manipulation of valves
and cocks provided for the purpose to separate the pumps and run
one side entirely independent of the other side. These dredges are
self-propelling and sea-going; some of them are fitted with immense
bins in which the dredged material is deposited, and when full, the
vessel propels herself out to deep water, dumps the sand or mud and
steams back to repeat the operation.
NOTE.—The operation of these machines is very interesting. A long
flexible tube 12 to 15 inches in diameter drops down from the side of
the vessel 20 to 30 feet or more to the bottom of the river or harbor
upon which the dredging operation is being performed. The upper end
of this tube is connected to an immense rotative centrifugal pump
revolving at several hundred revolutions per minute and capable of
handling many hundreds of tons of water per hour. The lower end of
the tube is manipulated from the vessel against the sand bars and mud
banks and as the water is sucked upward by the centrifugal pumps a
very large proportion of sand and mud goes with it. The centrifugal
pumps discharge this water with its suspended material into the tanks
on board the vessel or into scows, where the heavy material quickly
settles to the bottom, the water flowing back into the sea.
The mixture of sand and water which is drawn up the suction pipe is
forced a distance of 3,800 feet through a 30-inch pipe to the place
where it is to be deposited; the water draining off allows the solid
matter to remain.