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at either end. The extent of silencing is determined by the number of baffle plates, which are held together by a bolt passing through centre, though not held hard between the two end covers.

When using this form of silencer it is necessary

FIG. 164

FIG. 165

FIGS. 164, 165.-
.—EXHAUST SILENCER (JUSTICE)

to fix the box some feet from the engine to avoid 'back' pressure. It can be fixed in a horizontal or vertical position.

Fig. 168 is a section, and fig. 169 a cross section of another design of the same type, where the loose plates are held in

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position by bolts outside the main casting, instead of through the centre, the end covers pressing hard on the plates.

In every arrangement of exhaust silencer provision should be made for draining off the water which may collect through condensed gases or rain getting into the escape pipe. A convenient method is to arrange a moderate sized pocket in the form of a standpipe, arranged in the lowest position and fitted with a drain cock.

CHAPTER XXIII

GAS METERS

THE capacity of a meter is calculated by the number of lights, consuming 6 cubic feet per hour, it is designed to supply. Thus, a 5-light meter is capable of passing 30 cubic feet per hour, though meters are very often worked to a considerably higher capacity than that for which they are designed, and the dry form can be safely expected to give 11⁄2 times the duty stamped.

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The size of service pipes depends upon the distance and size of the main gas supply. If, however, the pressure of the gas is above, or not less than, 1 inch water pressure, and the distance from the main not more than 30 yards, the above meter sizes will be found suitable. It is advisable rather to increase the size of pipes to the meter than decrease them, and gas pipes of less than inch bore should never be placed in the ground.

REESE LIBRARY

OF THE

UNIVERSITY

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CHAPTER XXIV

GENERAL ARRANGEMENT OF ENGINE

FIG. 170 is an elevation and fig. 171 a plan of a 9 B.H.P. gas engine, giving a convenient arrangement of engine, tanks, &c.,

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but the varying conditions of space and machinery to be driven make it impossible to fix any definite arrangement to suit all

cases.

For the foundation, brick, stone, concrete, or wood is used; where convenient, concrete makes a good foundation, and admits of holding-down bolts having a firm hold.

It will be seen that two cooling tanks are used; the inlet and outlet of the water to the cylinder and combustion chamber are shown by the direction of the arrows. A number of vessels arranged so that the hot water from the cylinder and combustion chamber returns to the top of the first water vessel, falling to the bottom and rising up the partition and into the top of the second vessel, and falling again to the bottom and to the engine, makes a most efficient method of circulating. The capacity of these vessels equals 56 cubic feet. The way in which a gas engine is fixed has frequently a great influence upon its future running. If the air necessary for combustion flows into the cylinder through a long, continuous pipe, indifferent firing of the charges will probably follow, causing great loss in power and troublesome explosions. Large gas engines should be provided with an air regulator, which in most cases is fixed near the engine, although much better results are obtained by arranging regulator on the end of air pipe. In some cases much longer air pipes are used than when testing engine at the works. For this reason air pipes should always be larger beyond the air box.

Gas standing in ordinary gas pipes for any length of time becomes mixed with air by diffusion. If the mixture of gas and air is not allowed to flow out before attempting to start an engine, a difficulty will be experienced; and it will be found the best plan to always test the gas before attempting to start for the first time, or after it has been standing for a few days, and a cock should be fixed in the gas pipe near the gas cock, with a pipe leading to the under-side of the water inlet pipe, with a small cock attached, which will not only serve the purpose of testing the quality of the gas, but may be left burning in frosty weather to prevent the water in the circulating pipe from freezing. If, on lighting the gas at this cock, it burns with a blue

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