Chapter 3 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; Aimé Witz, in France; Dugald Clerk, Frederick Grover, and the late Bryan Donkin, in England; Güldner, 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.

Capacity. Normal hourly flow. Height, inches. Width, inches. Depth, inches. Diameter of pipe, inches. Power of engine to be fed.

burners cu. ft. in. in. in. in. h.-p.

3 14.726 13 11 913?16 0.590 1?2

5 24.710 18 133?4 105?8 0.787 3?4

10 49.420 211?4 181?2 129?16 0.984 1-2

20 98.840 233?16 1911?16 155?16 1.181 3-4

30 148.260 255?8 2111?16 183?16 1.456 5-6

50 247.100 291?2 245?16 207?16 1.592 7-10

60 296.520 305?16 255?8 255?8 1.671 11-14

80 395.360 335?16 305?16 271?8 1.968 15-19

100 494.200 35 337?16 2915?16 1.968 20-25

150 741.300 403?16 403?16 3313?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.

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.

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.

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.

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.

Fig. 44.-Rubber bag to prevent fluctuations of the ignition flame.

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.

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.

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.

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).

Fig. 50.

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.

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.

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.

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