With the exception of the and 1 H. P. sizes, which run at a speed of 180 revolutions per minute, these engines are all speeded to run at 160 revolutions. Instructions for Fixing the "Otto" Gas Engine. Always leave plenty of room to get at the fly wheel for starting. These engines, with the exception of the larger sizes, are frequently fixed on the upper floors of buildings, where they require no special foundation. When fixed on the ground floor or basement, no special foundation is necessary if the floor is concreted. Where there is only loose earth, stone blocks of from 9 inches to 12 inches thick should be laid at each end, or about 6 inches or 9 inches of concrete for the smaller sizes. For the larger engines, concrete 12 inches to 24 inches thick, or a stone bed about 24 inches thick, is required. For holding down, Lewis bolts are used with stone. When new concrete beds are laid, it is advisable to place a tube about 2 inches diameter temporarily round the bolt when filling in, to allow it to have a certain amount of play when the tube is withdrawn, so that the bolt can adapt itself to the position of the hole in engine bed when it is let down over the bolts. In cases where the concrete is already laid, bolts of sufficient length may be firmly fixed by arranging them head downwards in a hole made large enough to receive a stout washer, 4 inches to 6 inches square, which rests on the head at the bottom of the hole. This is filled in with cement, which holds the bolt firmly in position. As gas engines are often placed in dwelling houses, underneath offices, and in other places where no one would dream of fixing a steam engine and boiler, great care is often necessary to prevent the noise that is inseparable from the working of quick-running machinery, being conveyed to portions of the building where it would be objectionable. This can generally be effected by isolating the engine bed completely from the walls of the building, and by insulating any pipes or other material that is likely to convey the sound. The Sizes of Gas-Pipes for the various engines are given in the table of the sizes of gas engines. In fixing gas-pipes, all sharp elbows should be avoided. The Pipe for the Slide-Light should be taken, if possible, from a separate meter, or at some distance from the gas-bag if taken from the same pipe that supplies the engine. This is to provide against the possibility of the slide-lights being sucked out by the working of the engine itself. The Exhaust-Pipe should be carefully kept away from all woodwork, and on no account should the exhaust-box be placed on or close to wood, as the heat is likely to char it. The exhaust-pipe should be laid in such a manner that the water from condensation can easily flow away, and not lodge in the pipes to cause back pressure. The exhaust-pipe should discharge into the open air, not into a chimney, flue, or drain, lest damage arise from an accumulation of gas therein. The Water-Pipes should be arranged with an inclination of about 1 inch per foot from the engine to the water-vessel. During frosty weather, a gas jet should be kept burning close underneath the cylinder, to prevent the water in the jacket from freezing. The engine is provided with a governor, which performs two distinct. functions; it cuts off the gas both when the proper speed is exceeded, and when the engine stops. The piston is so constructed as to be capable of perfect adjustment, it being of primary importance that the piston should not leak. Consumption of Gas.-Regular working requires a certain proportion of gas to air, when the engine is working full power. The movement of the finger of the gas meter may be watched and the number of explosions counted, thus:-A nominal horse-power engine should make, say, 145 explosions per cubic feet of gas burned, and a 1 horse-power say 95 explosions; a 2 horse-power, say, 55; a 3 horse-power, say, 40; a 6 horsepower, say, 19; an 8 horse-power, say, 16; a 12 horse-power, say, 11; and a 16 horse-power, say, 6 explosions. One explosion occurs after each lift of the small gas valve. When full gas is used, the engines indicate much beyond their nominal power-a 16 horse indicating up to, say, 40 horse, and others as stated in the above table. Fine sperm oil is found to be the best lubricant for gas engines. Table 6.-SHOWING THE EFFICIENCY OF AN "OTTO" GAS ENGINE COMPARED WITH A STEAM ENGINE, EACH DEVELOPING 6 ACTUAL HORSE |