No two pipes should discharge into a T from opposite directions, thus
retarding the motion of both or one of the returning currents. This is
called “butting” and is one of the most vexatious things to encounter
in pipe fitting.
[Illustration: Fig. 131.]
[Illustration: Fig. 132.]
[Illustration: Fig. 133.]
All steam piped rooms should be frequently dusted, cleaned and kept
free from accumulation of inflammable material.
The use of the air valve is as follows: In generating steam from cold
water all the free air is liberated and driven off into the pipe, with
the air left in them, all of which is forced up to the highest point
of the coils or radiators, and compressed equal to the steam pressure
following it. Now, by placing a valve or vent at the return end of the
pieces to be heated, the air will be driven out by the compression. Why
the vent is placed at the return is, that the momentum of the steam, it
being the lightest body, will pass in the direction of it, falling down
into the return as it condenses, thus liberating the air. Otherwise,
should the vent not work, and the air is left in the radiator, it will
act as an air spring, and the contents of the pipes left stationary
will be the result; no circulation, no heat; and the greater steam
pressure put on, the greater the chances are of not getting any heat;
and thus a little device, with an opening no larger than a fine needle,
will start what a ton of pressure would not do in its absence.
If the drip and supply pipes are large there is very little danger of
freezing, provided suitable precautions are taken to leave the pipes
clear. They should be blown through, when left, and the steam valve
should be closed. There should also be a free chance for air to escape
in all systems of piping.
No rule can be given relating to capacity for heating pipes and
radiators which do not require to be largely modified by surroundings.
The field of steam heating would seem to be limitless—in one public
building it required recently 480,000 dollars to meet the expenditures
in this single line. As an example of warming on an extensive scale may
be taken a large office in New York, of which the following are the
particulars:
Total number of rooms, including halls and vaults. 286
Total area of floor surface. sq. ft. 137,370
Total volume of rooms. cub. ft. 1,923,590
A second example is furnished by the State Lunatic Asylum at
Indianapolis:
Length of frontage of building, more than. 2,000 lin. ft.
Total volume of rooms. 2,574,084 cub. ft.
Warming {indirect radiating surface 23,296
Apparatus {Direct 10,804
{Total 34,100 sq. ft.
Boilers {Grate area 180 sq. ft.
{Heating surface 5,863 sq. ft.
The “overhead” system of heating with steam pipes has several
advantages. 1. The pipes are entirely out of the way 2. They do not
become covered with odds and ends of unused materials. 3. If they leak
the drip fixes the exact location of place needed to be repaired. 4.
The room occupied overhead cannot be well otherwise utilized, hence in
shops the system has proved efficient.
But for offices or store rooms the overhead system is not approved of
owing to the heat beating down upon the occupants and causing headache.
When overhead heating pipes are used, they should not be hung too near
the ceiling. If the room be a high one, it is better to hang them
below, rather than above, the level of the belts running across the
room, and they should not be less than three or four feet from the
wall.
[Illustration: Fig. 134.]
It is important to protect all wood work or other inflammable material
around steam pipes from immediate contact with them, especially where
pipes pass through floors and partitions. A metal thimble should be
placed around the steam pipe, and firmly fastened on both sides of the
floor, in such a way as to leave an air space around the steam pipe.
For indirect radiating surfaces, the box coils are the forms most
used. The chambers or casings for containing them are made either of
brickwork, or often of galvanized sheet-iron of No. 26 gauge, with
folded joints. The coils are suspended freely within the chambers,
which are themselves attached to the walls containing the air inlet
flues. Besides coils of wrought iron tubes, cast-iron tablets or hollow
slabs, having vertical surfaces with projecting studs or ribs, have
been extensively used for the radiating surfaces.
As the amount of heat given off from the radiator cannot be
satisfactorily controlled by throttling the steam supply, it is usual
to divide all radiators into sections, each of which can be shut off
from the supply and return mains, separately from the rest of the
sections. This method of regulation applies to radiators for indirect
heating as well as for direct.
Vertical pipe coils, constitute a distinctive form of radiator now
largely used. In these a number of short upright 1-inch tubes, from
two feet 8 inches to 2 feet 10 inches long, are screwed into a hollow
cast iron base or box; and are either connected together in pairs by
return-bends at their upper ends, or else each tube stands singly with
its upper end closed, and having a hoop iron partition extending up
inside it from the bottom to nearly the top. The supply of steam is
admitted into the bottom casting; and the steam on entering, being
lighter than the air, ascends through one leg of each siphon pipe and
descends through the other, while the condensed water trickles down
either leg, and with it the displaced air sinks also into the bottom
box. For getting rid of the air, a trap is provided, having an outlet
controlled by metallic rods; as soon as all the air has escaped and the
rods become heated by the presence of unmixed steam, their expansion
closes the outlet.
A thorough drainage of steam pipes will effectually prevent cracking
and pounding noises.
The windward side of buildings require more radiating surface than does
the sheltered side.
When floor radiators are used, their location should be determined
by circumstances; the best situations are usually near the walls of
the room, in front of the windows. The cold air, which always creates
an indraft around the window frames, is thus, to some extent, warmed
as it passes over the the radiators, and also assists in the general
circulation.
Water of condensation will freeze quicker than water that has not been
evaporated, for the reason that it has parted with all its air and is
therefore solid.
Whatever the size of the circulating pipes, the supply and drip pipes
should be large, to insure good circulation; the drip pipes especially
so. This is also the more necessary when the pipes are exposed, or when
there is danger of freezing after the steam is shut off.
It is important to see that no blisters or ragged pipes go into the
returns, and also to make sure that the ends are not “burred in” with
a dull pipe cutter wheel so as to form a place of lodgment for loose
matter in the pipe to stop against.
[Illustration: Figs. 135-137.]
Experiments recently made on the strength of bent pipes have developed
some things not commonly known, or at least not recognized, that is,
the strain on the inside of the angles, _due to the effort of the
pipes to straighten themselves under pressure_. The problem is one of
considerable intricacy, resolvable, however, by computation, and is a
good one for practice. In the experiment referred to, a copper pipe of
6-3/4 in. bore, 3/16 in. thick, was used. The angle was 90 degrees, and
the legs about 16 in. long from the center. At a pressure of 912 pounds
to an inch, the deflection of the pipe was nearly 3/8 in., showing an
enormous strain on the inner side, in addition to the pressure.
Steam valves should be connected in such a manner that the valve closes
against the constant steam pressure.
Interesting experiments show that the loss by condensation in carrying
steam one mile is 5 per cent. of the capacity of the main, and a steam
pressure of seventy-five pounds carried in five miles of mains, ending
at a point one-half mile from the boiler house only shows a loss of
pressure of two pounds.
In steam warming it is necessary to bring the water to a boiling point
to get any heat whatever; in hot water warming, a low temperature will
radiate a corresponding amount of heat.
Never use a valve in putting in a low pressure apparatus if it is
possible to get along without it. All the valves or cocks that are
actually required in a well-proportioned low pressure apparatus are, a
cock to blow off the water and clean out the return pipes, another to
turn on the feed water. Of course the safety valves, gauge cocks, and
those to shut fire regulators and such as are a part of the boiler, are
not included in this “point.”
The most important thing in connecting the relief to return pipes is,
that it should always be carried down below the line, the same as all
vertical return pipes. In connecting the reliefs, so that the lower
opening can at any time be exposed to the steam, there will be the
difficulty of having the steam going in one direction, and the water in
another.
The relief pipe should “tap” the steam at its lowest or most depressed
points. It should always be put in at the base of all steam “risers”
taking steam to upper floors.
In leaving the boiler with main steam pipe, raise to a height that will
allow of one inch fall from the boiler to every ten feet of running
steam pipe; this is sufficient, and a greater fall or pitch will cause
the condensed water in the pipe to make at times a disagreeable noise
or “gurgling.”
The flow pipe should never start from the boiler in a horizontal
direction, as this will cause delay and trouble in the circulation.
This pipe should always start in a vertical direction, even if it
has to proceed horizontally within a short distance from the boiler.
Reflection will show that the perfect apparatus is one that carries
the flow pipe in a direct vertical line to the cylinder or tank; this
is never, or but rarely possible, but skill and ingenuity should be
exercised to carry the pipes as nearly as possible in this direction.
The flow of steam ought not to be fast enough to prevent the water of
condensation from returning freely. All the circulating pipes should be
lowest at the discharge end, and the inclination given them should not
be less than one foot in fifty.
[Illustration: Fig. 138.]
[Illustration: Fig. 139.]
[Illustration: Fig. 140.]
[Illustration: Fig. 141.]
The general rule is to lay the main pipes from the boiler so that the
pipe will drain from the boiler. Where this is done it is necessary to
have a drip just before the steam enters the circulation. This drip
is connected to a trap, or, if the condensed water is returned to the
boiler, the drip is arranged accordingly.
But it is the best practice to lay the main pipe with the lowest part
at the boiler, so that the drip will take care of itself, and not
require an extra trap, nor interfere with the return circulation.
When steam is turned into cold pipes the water of condensation gets
cold after running a short distance, and if it has to go through a
small drip pipe full of frost it will probably be frozen. Then, unless
it is followed up with a pail of hot water, the whole arrangement will
be frozen and a great many bursted pipes will result. Whenever turning
steam on in a system of very cold pipes, only one room should be taken
at a time, and a pail of hot water should be handy so that if the pipe
becomes obstructed it can be thawed immediately without damage.
When pipes become extensively frozen there is nothing to do but take
them out and put in new ones.
[Illustration: Fig. 142.]
[Illustration: Fig. 143.]
The manner in which a temperature too low to start rapid combustion
in wood in steam pipes, operates in originating a fire is by first
reducing the oxide of iron (rust) to a metallic condition. This is
possible only under certain external conditions, among them a dry
atmosphere. _Just as soon as the air is recharged with moisture, the
reduced iron is liable to regain, at a bound, its lost oxygen, and
in doing so become red hot._ This is the heat that sets the already
tindered wood or paper ablaze.
Where there is no rust there is no danger from fire with a less than
scorching temperature in the pipe or flue. Hence the necessity of
keeping steam or hot water fittings in good order.
The indirect system of heating is the most expensive to put in; as to
the cost of providing nearly double the heating surface in the coils
must be added the cost of suitable air boxes, pipes and registers. For
a large installation, this is a serious matter, although for office
warming the advantages gained on the score of healthfulness and greater
efficiency of employees much more than counterbalance the extra expense.
One horse power of boiler will approximately heat 6,000 to 10,000 cubic
feet in shops, mills and factories—dwellings require only one horse
power for from 10,000 to 20,000 cubic feet.
From seven to ten square feet of radiating surface can be heated from
_one square foot of boiler surface_, _i.e._, the heating surface of the
boiler and each horse power of boiler will heat 240 to 360 feet of
1-inch pipe.
The profession most nearly related to that of steam engineers is the
working steam fitters’ occupation. Strictly speaking, the engineer
should produce the steam, and it is the steam fitters’ place to fix
up all the steam pipes and make all the necessary connections: but
where the steam plants are small, the engineer may be steam fitter
also: hence the introduction in this work of these “Points” which are
necessary to be known for the proper care and management of any system
of steam or hot water heating.
The care and patience, the mental strain and not infrequently the
physical torture incident to fitting up a complicated pipe system
cannot adequately be set forth in words.
It is stated to be a fact, that in high pressure hot water heating the
water frequently becomes red hot, pressures of 1000 to 1200 pounds per
square inch being reached, and when the circulation of the system is
defective the pipe becomes visibly red in the dark.
Pipes under work benches should be avoided, unless there is an opening
at the back to permit the escape of the heated air, which would
otherwise come out at the front.
When both exhaust and live steam are used for heating, many engineers
prefer to use independent lines of pipe for each, rather than run
the risk of interference and waste caused by admitting exhaust and
live steam into the same system at the same time. Nevertheless, the
advantages gained by being able to increase the heating power of a
system in extremely cold weather by utilizing the entire radiating
surface for high pressure steam, are so great that it is probably
better so to arrange the system of pipes and connections that this can
be done.
Double extra heavy pipe (XX) is used for ice and refrigerating machines
(see page 246), as a general rule, makers of this class of machinery
obtain but little satisfaction in the use of the ordinary thread
joining and use special dies _with uniform taper_—both for couplings,
flanges and threading the pipe itself. They do this to protect their
reputation and guarantees.
_Welding boiler and other tubes._—The following is a good way in cases
of emergency and can be done on a common forge:
Enlarge one end of the shortest piece, and one end of the long piece
make smaller, then telescope the two about 3/4 of an inch. Next get an
iron shaft as large as will go into the tube and lay across the forge
with the tube slipped over it. _Block the shaft up so that the tube
will hang down from the top of the shaft._ By such an arrangement the
inside of the tube will be smooth for a scraper. When the tube gets to
a welding heat strike on the _end_ of the short piece first, with a
heavy hammer, then with a light and broad-faced hammer make the weld.
Borax can be used to good advantage, but it is not necessary. The next
thing is to test the tube, which can be done in the following manner:
Drive a plug in one end of the tube, stand it up on that end, and fill
it with water, if it does not leak the job is well done, if a leak
exists the welding must be again done.