A. It is intended to prevent the too rapid movement of the intercepting valve which might damage the valve or seat, and it is necessary that the dash-pot should be full of oil to make it work properly.
4. Q. Explain how a Schenectady two-cylinder compound may be operated as a simple engine.
A. To operate the compound as a simple engine, the separate exhaust valve is opened which will cause the intercepting valve to move and stay in position to allow the high-pressure cylinder to exhaust direct to the atmosphere and admits live steam at a reduced pressure to the low-pressure cylinder. This should be done when starting a train or when moving very slowly and about to stall on a grade. The engine should not be operated simple while running except when at low speed.
5. Q. Explain how a two-cylinder compound is changed from simple to compound.
A. Place the handle of the three-way cock or simpling valve in the cab so as to release the air from the cylinder of the separate exhaust valve. A coiled spring will then close this valve. This permits the exhaust steam of the high-pressure cylinder to accumulate in the receiver until sufficient pressure is obtained to force the intercepting valve into compounding position. This shuts off live steam from the low-pressure cylinder and allows exhaust steam from the high-pressure cylinder to feed through the receiver into the low-pressure steam chest.
6. Q. How should a compound engine be lubricated?
A. One-third more oil should be fed to the high than the low-pressure cylinder, using more oil at high speed than at slow.
7. Q. Why feed more oil to high than to a low-pressure cylinder?
A. Because some of the oil from the high-pressure cylinder follows the steam into the low-pressure cylinder.
8. Q. How would you lubricate the valve of low-pressure cylinder if the oil feed became inoperative on that side?