THE INSTALLATION OF AN ENGINE
In the preceding chapter the various structural details of an engine
have been summarized and those arrangements indicated which, from a
general standpoint, seem most commendable. No particular system has been
described in order that this manual might be kept within proper limits.
Moreover, the best-known writers, such as Hutton, Hiscox, Parsell and
Weed, in America; Aime Witz, in France; Dugald Clerk, Frederick Grover,
and the late Bryan Donkin, in England; Gueldner, Schottler, Thering, in
Germany, have published very full descriptive works on the various types
of engines.
We shall now consider the various methods which seem preferable in
installing an engine. The directions to be given, the author believes,
have not been hitherto published in any work, and are here formulated,
after an experience of fifteen years, acquired in testing over 400
engines of all kinds, and in studying the methods of the leading
gas-engine-building firms in the chief industrial centers of Europe and
America.
=Location.=--The engine should be preferably located in a well-lighted
place, accessible for inspection and maintenance, and should be kept
entirely free from dust. As a general rule, the engine space should be
enclosed. An engine should not be located in a cellar, on a damp floor,
or in badly illuminated and ventilated places.
=Gas-Pipes.=--The pipes by which fuel is conducted to engines, driven by
street-gas, and the gas-bags, etc., are rarely altogether free from
leakage. For this reason, the engine-room should be as well ventilated
as possible in the interest of safety. Long lines of pipe between the
meter and the engine should be avoided, for the sake of economy, since
the chances for leakage increase with the length of the pipe. It seldom
happens that the leakage of a pipe 30 to 50 feet long, supplying a 30
horse-power engine, is much less than 90 cubic feet per hour. The
beneficial effect of short supply pipes between meter and engine on the
running of the engine is another point to be kept in mind.
An engine should be supplied with gas as cool as possible, which
condition is seldom realized if long pipe lines be employed, extending
through workshops, the temperature of which is usually higher than that
of underground piping. On the other hand, pipes should not be exposed to
the freezing temperature of winter, since the frost formed within the
pipe, and particularly the crystalline deposition of naphthaline,
reduces the cross section and sometimes clogs the passage. Often it
happens that water condenses in the pipes; consequently, the piping
should be disposed so as to obviate inclines, in which the water can
collect in pockets. An accumulation of water is usually manifested by
fluctuations in the flame of the burner. In places where water can
collect, a drain-cock should be inserted. In places exposed to frost, a
cock or a plug should be provided, so that a liquid can be introduced to
dissolve the naphthaline. To insure the perfect operation of the engine,
as well as to avoid fluctuations in nearby lights, pipes having a large
diameter should preferably be employed. The cross-section should not be
less than that of the discharge-pipe of the meter, selected in
accordance with the prescriptions of the following table:
GAS-METERS.
Table Headings--
Column A: Capacity.
Column B: Normal hourly flow.
Column C: Height.
Column D: Width.
Column E: Depth.
Column F: Diameter of pipe.
Column G: Power of engine to be fed.
_________________________________________________________________
| | |
| | Dimension in inches. |
| |_______________________________________|
| | | | | |
A. | B. | C. | D. | E. | F. | G.
________|_________|_________|__________|__________|_______|______
| | | | | |
burners | cu. ft. | | | | | h.-p.
3 | 14.726 | 13 | 11 | 9-13/16 | 0.590 | 1/2
5 | 24.710 | 18 | 13-3/4 | 10-5/8 | 0.787 | 3/4
10 | 49.420 | 21-1/4 | 18-1/2 | 12-9/16 | 0.984 | 1-2
20 | 98.840 | 23-3/16 | 19-11/16 | 15-5/16 | 1.181 | 3-4
30 | 148.260 | 25-5/8 | 21-11/16 | 18-3/16 | 1.456 | 5-6
50 | 247.100 | 29-1/2 | 24-5/16 | 20-7/16 | 1.592 | 7-10
60 | 296.520 | 30-5/16 | 25-5/8 | 25-5/8 | 1.671 | 11-14
80 | 395.360 | 33-5/16 | 30-5/16 | 27-1/8 | 1.968 | 15-19
100 | 494.200 | 35 | 33-7/16 | 29-15/16 | 1.968 | 20-25
150 | 741.300 | 40-3/16 | 40-3/16 | 33-13/16 | | 30-40
________|_________|_________|__________|__________|_______|______
The records made are exact only when the meters (Fig. 40) are installed
and operated under normal conditions. Two chief causes tend to falsify
the measurements in wet meters: (1) evaporation of the water, (2) the
failure to have the meter level.
Evaporation occurs incessantly, owing to the flowing of the gas through
the apparatus, and increases with a rise in the temperature of the
atmosphere surrounding the meter. Consequently this temperature must be
kept down, for which reason the meter should be placed as near the
ground as possible. The evaporation also increases with the volume of
gas delivered. Hence the meter should not supply more than the volume
for which it was intended. In order to facilitate the return of the
water of condensation to the meter and to prevent its accumulation, the
pipes should be inclined as far as possible toward the meter. The
lowering of the water-level in the meter benefits the consumer at the
expense of the gas company.
[Illustration: FIG. 40.--Wet gas-meter.]
Inclination from the horizontal has an effect that varies with the
direction of inclination. If the meter be inclined forward, or from left
to right, the water can flow out by the lateral opening at the level,
and incorrect measurements are made to the consumer's cost.
During winter, the meter should be protected from cold. The simplest way
to accomplish this, is to wrap substances around the meter which are
poor conductors of heat, such as straw, hay, rags, cotton, and the like.
Freezing of the water can also be prevented by the addition of alcohol
in the proportion of 2 pints per burner. The water is thus enabled to
withstand a temperature of about 5 degrees F. below zero. Instead of
alcohol, glycerine in the same proportions can be employed, care being
taken that the glycerine is neutral, in order that the meter may not be
attacked by the acids which the liquid sometimes contains.
[Illustration: FIG. 41.--Dry gas-meter.]
=Dry Meters.=--Dry meters are employed chiefly in cold climates, where
wet meters could be protected only with difficulty and where the water
is likely to freeze. In the United States the dry meter is the type most
widely employed. In Sweden and in Holland it is also generally
introduced (Fig. 41).
In the matter of accuracy of measurement there is little, if any,
difference between wet and dry meters. The dry meter has the merit of
measuring correctly regardless of the fluctuations in the water level.
On the other hand, it is open to the objection of absorbing somewhat
more pressure than the wet meter, after having been in operation for a
certain length of time. This is an objection of no great weight; for
there is always enough pressure in the mains and pipes to operate a
meter.
[Illustration: FIG. 42.--Section through a dry gas-meter.]
In many cases, where the employment of non-freezing liquids is
necessary, the dry meter may be used to advantage, since all such
liquids have more or less corroding effect on sheet lead and even tin,
depending upon the composition of the gas.
[Illustration: FIG. 43.--Section through a dry gas-meter.]
The dry meter comprises two bellows, operating in a casing divided into
two compartments by a central partition. The gas is distributed on one
or the other side of the bellows, by slides _B_. The slides _B_ are
provided with cranks _E_, controlled by levers _M_, actuated by
transmission shafts _O_, driven by the bellows. The meter is adjusted by
a screw which changes the throw of the cranks _E_ and consequently
affects the bellows. The movement of the crank-shaft _D_ is transmitted
to the indicating apparatus. In order to obviate any leakage, this shaft
passes through a stuffing-box, _G_. The diagrams (Figs. 42-43) show the
construction of a dry meter, the arrows indicating the course taken by
the gas.
[Illustration: FIG. 44.--Rubber bag to prevent fluctuations of the
ignition flame.]
[Illustration: FIG. 45.--Rubber bags on gas-pipes.]
Care should be taken to provide the gas-pipe with a drain-cock, at a
point near the engine. By means of this cock, any air in the pipe can be
allowed to escape before starting; otherwise the engine can be set in
motion only with difficulty. If the engine be provided with an
incandescent tube, the gas-supply pipe of the igniter should be fitted
with a small rubber pouch or bag, in order to obviate fluctuations in
the burner flame, caused by variations in the pressure (Fig. 44). As a
general rule, the supply-pipe should be connected with the main pipe on
the forward side of the bags and gas-governors. The main pipe and all
other piping near the engine should extend underground, so that free
access to the motor from all sides can be obtained, without possibility
of injury.
=Anti-pulsators, Bags, Pressure-Regulators.=--The most commonly employed
means of preventing fluctuation of nearby lights, due to the sharp
strokes of the engine, consists in providing the gas-supply pipe with
rubber bags (Fig. 45), which form reservoirs for the gas and, by reason
of their elasticity, counteract the effect produced by the suction of
the engine. Nevertheless, in order to insure a supply of gas at a
constant pressure, which is necessary for the perfect operation of the
engine, there are generally used, in addition to the bags, devices
called gas-governors, or anti-pulsators (Fig. 46).
Although these devices are constructed in different ways, the underlying
principle is the same in all. They comprise a metallic casing,
containing a flexible diaphragm of rubber or of some fabric impermeable
to gas. Suction of the engine creates a vacuum in the casing. The
diaphragm bends, thereby actuating a valve, which cuts off the gas
supply. During the three following periods (compression, explosion, and
exhaust) the gas, by reason of its pressure on the diaphragm, opens the
valve and fills the casing, ready for the next suction stroke.
[Illustration: FIG. 46.--An anti-pulsator.]
Other devices, which are never sold with the engine, but are rendered
necessary by reason of the conditions imposed by the gas supply are sold
under the name "pressure-regulators" (Fig. 47). They consist of a bell,
floating in a reservoir containing water and glycerine (or mercury), and
likewise actuate a valve which partially controls the flow of gas. This
valve being balanced, its mechanical action is the more certain. Such
devices are very effective in maintaining the steadiness of lights. On
the other hand, they are often an obstacle to the operation of the
engine because they reduce the flow and pressure of the gas too much. In
order to obviate this difficulty, a pressure-regulator should be chosen
with discrimination, and of sufficiently large size to insure the
maintenance of an adequate supply of gas to the engine. Frequent
examinations should be made to ascertain if the bell of the regulator is
immersed in the liquid. In the case of anti-pulsators, care should be
taken that they are not spattered with oil, which has a disastrous
effect on rubber. Anti-pulsators are generally mounted about 4 inches
from a wall, in order that the diaphragm may be actuated by hand, if
need be.
[Illustration: FIG. 47.--A pressure-regulator.]
=Precautions.=--In order not to strain the rubber of the bags or of the
anti-pulsators, it is advisable to place a stop-cock in advance of these
devices so that they can not be filled while the motor is at rest.
The capacity of the rubber bags that can be bought in the market being
limited, it is necessary to place one, two, or three extra bags in
series (Figs. 48 and 49), for large pipes; but it should be borne in
mind that the total section of the branch pipes should be at least equal
to that of the main pipe. It is also advisable to extend the tube
completely through the bag as shown in Figs. 48 and 49.
[Illustration: FIGS. 48-49.--Arrangement of rubber bags.]
If there be two branch pipes the minimum diameter which meets this
requirement is ascertained as follows: Draw to any scale a semicircle
having a diameter equal or proportional to that of the main pipe (Fig.
50). The sides of the isosceles triangle inscribed within this
semicircle give the minimum diameter of each of the branch pipes.
Sometimes engines are provided with a cock having an arrangement by
means of which the gas feed is permanently regulated, according to the
quality and pressure of the gas and according to the load at which the
engine is to run. This renders it possible to open the cock always to
the same point (Fig. 51).
[Illustration: FIG. 50.]
[Illustration: FIG. 51.]
=Air Suction.=--In a special chapter the precautions to be taken to
counteract the influence of the suction of the engine in causing
vibration will be treated. The manner in which the suction of air is
effected necessarily has as marked an influence on the operation of the
engine as the supply of gas, since air and gas constitute the explosive
mixture.
Resistance to the suction of air should be carefully avoided, for which
reason the length of the pipe should be reduced to a minimum, and its
cross-section kept at least equal to that of the air inlet of the
engine. Since the quality of street-gas varies with each city, the
proper proportions of gas and air are not constant. In order that these
proportions may be regulated, it is a matter of some importance to fit
some suitable device on the pipe. Good engines are provided with a plug
or flap valve. Generally the air-pipe terminates either in the hollowed
portion of the frame, or in an independent pot, or air chest. The first
arrangement is not to be recommended for engines over 20 to 25
horse-power. Accidents may result, such as the breaking of the frame by
reason of back firing, of which more will be said later. If an
independent chest be employed, its closeness to the ground renders it
possible for dust easily to pass through the air-holes in the walls at
the moment of suction, and even to enter the cylinder, where its
presence is particularly harmful, leading, as it does, to the rapid wear
of the rubbing surfaces. This evil can be largely remedied by filling
the air-chest with cocoa fiber or even wood fiber, provided the latter
does not become packed down so as to prevent the air from passing
freely. Such fibers act as air-filters. Regular cleaning or renewal of
the fiber protects the cylinder from wear. In a general way, care should
be taken, before fitting both the gas and air pipes, to tap the pipes,
elbows, and joints lightly with a hammer on the outside in order to
loosen whatever rust or sand may cling to the interior; otherwise this
foreign matter may enter the cylinder and cause perturbations in the
operation of the engine. Under all circumstances, care should be taken
not to place the end of the air-pipe under the floor or in an enclosed
space, because leakage may occur, due to the bad seating of the
air-valve, thereby producing a mixture which may explode if the flame
leaps back, as we shall see in the discussion of suction by pipes
terminating in the hollow of the frame. On the other hand, sand or
sawdust should not be sprinkled on the floor.
=Exhaust.=--For the exhaust, cast-iron or drawn pipes as short as
possible should be used. Not only the power of the engine, but also its
economic consumption, can be markedly affected by the employment of long
and bent pipes. Resistance to the exhaust of the products of combustion
not only causes an injurious counter-pressure, but also prevents the
clearing of the cylinder of burnt gases, which contaminate the aspired
mixture and rob it of much of its explosiveness. The necessity of
evacuating the cylinder as completely as possible is, nevertheless, not
always reconcilable with local surroundings. To a certain extent, the
objections to long exhaust-pipes are overcome by rigorously avoiding the
use of elbows. Gradual curves are preferable. In the case of very long
pipes it is advisable to increase their diameter every 16 feet from the
exhaust. The exhaust-chest should be placed as near as possible to the
engine; it should never be buried; for the joints of the inlet and
outlet pipes of the exhaust-chest should be easily accessible, so that
they may be renewed when necessary. The author recommends the placing
of the exhaust-chest in a masonry pit, which can be closed with a
sheet-metal cover. For engines of 20 horse-power and upward, these
joints should be entirely of asbestos. Pipes screwed directly into the
casting are liable to rust. Exposed as they are to the steam or water of
the exhaust, they cannot be detached.
[Illustration: FIG. 52.--Method of mounting pipes.]
The water, which results from the combination of the hydrogen of the gas
with the oxygen of the air, is deposited in most cases at the bottom of
the exhaust-chest. It is advisable to fit a plug or iron cock in the
base of the chest. Alkaline or acid water will always corrode a bronze
cock. In order that the pipes may not also be attacked, they are not
disposed horizontally, but are given a slight incline toward the point
where the water is drained off. If pipes of some length be employed,
they should be able to expand freely without straining the joints, as
shown in the accompanying diagram (Fig. 52), in which the exhaust-chest
rests on iron rollers which permit a slight displacement.
For the sake of safety, at least that portion of the piping which is
near the engine should be located at a proper distance from woodwork and
other combustible material. By no means should the exhaust discharge
into a sewer or chimney, even though the sewer or chimney be not in use;
for the unburnt gases may be trapped, and dangerous explosions may ensue
at the moment of discharge.
The joints or threaded sleeves employed in assembling the exhaust-pipe
should be tested for tightness. The combined action of the moisture and
heat causes the metal to rust and to deteriorate very rapidly at leaky
spots.
When several engines are installed near one another, each should be
provided with a special exhaust-pipe; otherwise it may happen, when the
engines are all running at once, that the products of combustion
discharged by the one may cause a back pressure detrimental to the
exhaust of the next.
It is possible to employ a pipe common to all the exhausts if the pipe
starts from a point beyond the exhaust-chests, in which case Y-joints
and not T-joints are to be used.
The manner of securing the pipes to walls by means of detachable
hangers, lined with asbestos, is shown in a general way in the
accompanying Fig. 53. The object of this arrangement is to render
detachment easy and to prevent the transmission of shocks to the
masonry.
The precautions to be taken for muffling the noise of the exhaust will
be discussed later.
The end of the exhaust-pipe should be slightly curved down in order to
prevent the entrance of rain. Exhaust-pipes are subjected to
considerable vibration, due to the sudden discharge of the gases. To
protect the joints, the pipes should be rigidly fastened in place.
[Illustration: FIG. 53.--Method of securing pipes to walls.]
=Legal Authorization.=--In most countries gas-engines may be installed
only in accordance with the provision of general or local laws, which
impose certain conditions. These laws vary with different localities,
for which reason they are not discussed here.