Chapter 8 HOW TO START AN ENGINE-PRELIMINARY PRECAUTIONS

The first step which is taken in starting an engine driven by street-gas is, naturally, the opening of the meter-cock and the valves between the meter and the engine. When the gas has reached the engine, the rubber bags will swell up and the anti-pulsator diaphragm will be forced out. The drain-cock of the gas-pipe is then opened. In order to ascertain whether the flow of gas is pure, a match is applied to the outlet of the cock. The flame is allowed to burn until it changes from its original blue color to a brilliant yellow.

If the hot-tube system of ignition be employed, the Bunsen burner is ignited, care being taken that the flame emerging from the tube is blue in color. If necessary the admission of air to the burner is regulated by the usual adjusting-sleeve. A white or smoky flame indicates an insufficient supply of air to the burner. A characteristic sooty odor is still other evidence of the same fact. Sometimes a white flame may be produced by the ignition of the gas at the opening of the adjusting-sleeve. A blue or greenish flame is that which has the highest temperature and is the one which should, therefore, be obtained. About five or ten minutes are required to heat up the tube, owing to the material of which it is made. When the proper temperature has been attained the tube becomes a dazzling cherry red in color. While the tube is being heated up, it is well to determine whether the engine is properly lubricated and all the cups and oil reservoirs are duly filled up. The cotton waste of the lubricators should be properly immersed, and the drip lubricators examined to determine whether they are supplying their normal quantity of oil.

The regulating-levers of the valves should be operated in order to ascertain whether the valves drop upon their seats as they should. The stem of the exhaust-valve should be lubricated with a few drops of petroleum.

If the ignition system employed be of the electric type, with batteries and coils, tests should be made to determine whether the current passes at the proper time on completing the circuit with the contact mounted on the intermediary shaft. This contact should produce the characteristic hum caused by the operation of the coil.

If a magneto be used in connection with the ignition apparatus, its inspection need not be undertaken whenever the engine is started, because it is not so likely to be deranged. Still, it is advisable, as in the case of ignition by induction-coils, to set in position the device which retards the production of the spark. This precaution is necessary in order to avoid a premature explosion, liable to cause a sharp backward revolution of the fly-wheel.

After the ignition apparatus and the lubricators have been thus inspected, the engine is adjusted with the piston at the starting position, which is generally indicated by a mark on the cam-shaft. The starting position corresponds with the explosion cycle and is generally at an angle of 40 to 60 degrees formed by the crank above the horizontal and toward the rear of the engine. The gas-cock is opened to the proper mark, usually shown on a small dial. If there be no mark, the cock is slowly opened in order that no premature explosion may be caused by an excess of gas.

The steps outlined in the foregoing are those which must be taken with all motors. Each system, however, necessitates peculiar precautions, which are usually given in detailed directions furnished by the builder.

As a general rule the engines are provided on their intermediary shafts with a "relief" or "half-compression" cam. By means of this cam the fly-wheel can be turned several times without the necessity of overcoming the resistance due to complete compression. Care should be taken, however, not to release the cam until the engine has reached a speed sufficient to overcome this resistance.

Engines of considerable size are commonly provided with an automatic starting appliance. In order to manipulate the parts of which this appliance is composed, the directions furnished by the manufacturer must be followed. Particularly is this true of automatic starters comprising a hand-pump by means of which an explosive mixture is compressed,-true because in the interests of safety great care must be taken.

The tightness and free operation of the valves or clacks which are intended to prevent back firing toward the pump should be made the subject of careful investigation. Otherwise, the piston of the pump is likely to receive a sudden shock when back firing occurs.

When the engine has been idle for several days, it is advisable, before starting, to give it several turns (without gas) in order to be sure that all its parts operate normally. The same precaution should be taken in starting an engine, if a first attempt has failed, in order to evacuate imperfect mixtures that may be left in the cylinder. Before this test is made, the gas-cock should, of course, be closed in order to prevent an untimely explosion. It is advisable in starting an engine not to bend the body over the ignition-tube, because the tube is likely to break and to scatter dangerous fragments.

Under no condition whatever should the fly-wheel be turned by placing the foot upon the spokes. All that should be done is to set it in motion by applying the hand to the rim.

Care During Operation.-When the engine has acquired its normal speed, the governor should be looked after in order that its free operation may be assured and that all possibility of racing may be prevented. After the engine has been running normally for a time, the cocks of the water circulation system should be manipulated in order to adjust the supply of water to the work performed by the engine. In other words the cylinder should be kept hot, but not burning, as previously explained in the paragraph in which the water-jacket is discussed. The maintenance of a suitable temperature is extremely important so far as economy is concerned. All the bearings should be inspected in order that hot boxes may be obviated.

Stopping the Engine.-The steps to be taken in stopping the engine are the following:

1. Stopping the various machines driven by the engine,-a practice which is followed in the case of all motors;

2. Throwing out the driving-pulley of the engine itself, if there be one;

3. Closing the cock between the meter and the gas-bags in order to prevent the escape of gas and the useless stretching of the rubber of the bags or of the anti-pulsating devices;

4. Actuating the half-compression or relief cam as the motor slows down, in order to prevent the recoil due to the compression;

5. Closing the gas-admission cock;

6. Shutting off the supply of oil of free flowing lubricators, and lifting out the cotton from the others.

If the engine be used to drive a dynamo, particularly a dynamo provided with metal brushes, the precaution should be taken of lifting the brushes before the engine is stopped in order to prevent their injury by a return movement of the armature-shaft;

7. Shutting off the cooling-water cock if running water is used.

If the engine is exposed to great cold, the freezing of the water in the jacket is prevented while the engine is at rest, either by draining the jacket entirely, or by arranging a gas jet or a burner beneath the cylinder for the purpose of causing the water to circulate. If such a burner be used the cocks of the water supply pipe should, of course, be left open.

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