=COMPOUND LOCOMOTIVES=
1. Q. Wherein do compound locomotives differ from ordinary or simple ones?
A. Simple engines take live steam from the boiler and after one expansion in a single cylinder it is exhausted to the atmosphere. A compound engine has two cylinders, sometimes one on each side of the locomotive; other types have four cylinders or two on each side of the locomotive. The live steam first pa.s.ses into one cylinder, expanding down for a portion of its pressure, and then being allowed to pa.s.s into the second cylinder where it expands a second time, thus getting two expansions from each volume of live steam. Both simple and compound locomotives consist of two engines coupled to the same set of driving wheels. Balanced compounds have four sets of main rods and crank pins.
Mallet compounds have two complete sets of engines under one boiler.
2. Q. Why is one cylinder on a compound locomotive called the high-pressure cylinder and the other one a low-pressure cylinder?
A. The high-pressure cylinder takes that name because it works live steam direct from the boiler at high pressure. The low-pressure cylinder receives the steam after the first expansion and works with a low pressure. It is always larger than its companion high-pressure cylinder in order to get the same power from the low-pressure steam.
3. Q. In the Schenectady two-cylinder compound, what is the duty of the oil dash-pot?
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 c.o.c.k 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 acc.u.mulate 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?
A. Feed an increased quant.i.ty through the oil pipe to the intercepting valve. Shut the engine off occasionally and cut into simple position.
Oil will then go direct from the intercepting valve into the low-pressure steam chest and cylinders. This would avoid going out on steam chest to oil by hand.
9. Q. How much water should be carried in the boiler of a compound locomotive?
A. A very moderate level, never allowing it to get so high that moist steam will pa.s.s through the cylinders, because for satisfactory service a compound engine should always have dry steam.
10. Q. How should a compound locomotive be started with a long train?
A. In simple position with cylinder c.o.c.ks open.
11. Q. When drifting what should be the position of the separate exhaust valve, the cylinder and port c.o.c.ks?
A. Open position.
12. Q. What will cause two exhausts of air to blow from the three-way c.o.c.k or simpling valve in the cab when the engine is being changed to compound?
A. A sticky exhaust valve. It does not move when air is first discharged. The second exhaust comes when it does move.
13. Q. What does steam blowing at the three-way c.o.c.k indicate?
A. The separate exhaust valve not seating properly caused by stuck valves, a weak or broken spring, or the packing rings of separate exhaust valve leaking.
14. Q. What can be done if the engine will not operate compound when the air pressure on the separate exhaust valve is released by the three-way c.o.c.k?
A. The separate exhaust valve has failed to close. Try jarring it with a hammer on the front side, near the exhaust valve. With a bad case, take the valve out, clean it and replace, if not broken.
15. Q. If the engine stands with high-pressure side on the dead center and will not move when given steam, where is the trouble, and what may be done to start the engine? Why?
A. The intercepting valve is stuck in compound position, so live steam cannot get to the low-pressure cylinder. In a case of this kind, close the throttle, open cylinder and port c.o.c.ks; when all pressure is relieved, use a bar to move forward the rod that works through the oil dash-pot, thus moving the valve to simple position and steam will pa.s.s to the low-pressure cylinder as soon as throttle is open. The engine will not start, because with the low-pressure piston on the quarter, steam must be admitted to its cylinder to start the engine.
16. Q. In the event of a breakdown, how should one disconnect?
A. The same as a simple engine with separate exhaust valve open, so engine will work simple instead of compound.
17. Q. What may be done to shut off steam pressure from the steam chest and low-pressure cylinder?
A. To shut off steam from the low-pressure chest, pull out the rod that runs through the dash-pot as far as possible and fasten it in this position. Then open the separate exhaust valve.
18. Q. Is it important that air be pumped up on a two-cylinder compound before the engine is moved? Why?
A. Yes. Because the separate exhaust valve is opened by air pressure and the engine cannot be simpled without sufficient pressure.
19. Q. How are the blows in a compound located?
A. The same as in a simple engine with the exception that any blow on the high-pressure side will not be heard when the separate exhaust valve is closed. A blow on the high-pressure side will increase the pressure in the low-pressure side, so relief valves will pop on low-pressure side when working compound with full throttle.
20. Q. What should be done if high-pressure piston of a cross compound is broken off the rod, or if the high-pressure or low-pressure cylinder head is broken?
A. Cover the ports on that side, open separate exhaust valve and run in; use live steam in low-pressure cylinder only, for the broken piston.
With broken cylinder head, would cover ports on that side. Open separate exhaust and run in with low-pressure side. Would not take down main rod, but would take out pop valves in both cylinder heads and see that the cylinder is properly oiled. For low-pressure head broken, would cover ports on that side, open separate exhaust valve and use high-pressure side; need not take down main rod, but would see that the cylinder is well oiled.
21. Q. In the event of separate exhaust valves failing to work when throttle is wide open, what can be done to a.s.sist in opening?
A. Ease throttle off very fine to reduce the receiver pressure; in a moment or two the separate exhaust valve should then move. If this did not work, would shut off entirely, even at the risk of stalling, as in that event the train could be started again with engine cut in simple.
22. Q. If a transmission bar on a cross compound is broken, what would you do for the right side? For the left side?
A. For right side would cover ports on that side, take out pop from cylinder head, open separate exhaust and run in with other cylinder. For left side, cover ports and fasten valve stem same as for right side.
Would leave main rods up, keep separate exhaust open in both cases and see that cylinder is well oiled.
23. Q. In the event of a cross compound beginning to jerk badly and cylinder head pops in low-pressure cylinder popping, where would you look for the trouble?
A. That either the high-pressure valve or piston packing was blowing live steam into the receiver and then into low-pressure steam chest. If possible would locate trouble and report accordingly.
24. Q. If during a trip you found the piston valve rings of a cross compound were broken, what would you do?