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 passes into one cylinder, expanding down for a portion of its pressure, and then being allowed to pass 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 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?
A. Feed an increased quantity 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 pass 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 cocks open.
11. Q. When drifting what should be the position of the separate exhaust valve, the cylinder and port cocks?
A. Open position.
12. Q. What will cause two exhausts of air to blow from the three-way cock 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 cock 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 cock?
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 cocks; 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 pass 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 assist 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?
A. If nothing but rings were broken, would reduce boiler pressure about 25 per cent. and go on with my train if possible.
25. Q. If piston valve on cross compound was broken so it became necessary to remove it, what should you do?
A. Remove the broken piston valve, reduce boiler pressure to 100 pounds and proceed.
26. Q. What is the difference between a Vauclain four-cylinder compound, a four-cylinder tandem, a balanced and a Mallet compound in their arrangement of cylinders?
A. A Vauclain compound has two cylinders on each side, one above the other, and both piston rods connected to one cross-head. A four-cylinder tandem has four cylinders, the high pressure being ahead of the low pressure on each side, and both pistons connected to one piston rod and one cross-head. A balanced compound has four cylinders, the two high-pressure cylinders being between the frames, each having a main rod connected to a crank axle. The two low-pressure cylinders are located outside the frame, each having a main rod and crank pin connected to the driving wheel center. A Mallet compound consists of two separate and independent engines, one fixed to the boiler, the other swinging from a center and sliding back and forth under the front end of the boiler. The rear engine works steam at high pressure; steam from this engine exhausts through a receiver pipe having flexible joints to the forward engine which works the steam at low pressure, then exhausts it to the front end and stack.
27. Q. How many main steam valves has each type?
A. The Vauclain has one valve on each side, distributing steam to the high and low-pressure cylinder on that side. The four-cylinder tandem has two valves on each side, one for each of the two cylinders. A Baldwin balanced compound has two valves the same as the Vauclain. The American balanced compound has four valves, one for each cylinder, the two valves for one side of the engine being connected to one valve rod. A Mallet compound has a separate valve for each cylinder the same as a simple locomotive.
28. Q. How do you test for blow in high and low-pressure cylinder packing for each type of compound engine?
A. Simple the engine if a cross compound, then make test the same as for a simple engine. For Vauclain four-cylinder compounds, test low pressure first. A blow past the low-pressure piston will show the same as on a simple engine; a blow past the high-pressure piston will make the engine stronger on that side when working a full throttle and the exhaust from the low-pressure cylinder will be heavier. To test the valve on either side, cover the ports. Broken packing rings in the steam valve will show a blow in one position and be tight in another. For tandem compound, to test high-pressure piston packing, stand engine on the top quarter, lever in back gear, drivers blocked and starting valve closed; remove back indicator plug or open back cylinder cock of high-pressure cylinder. Steam coming from the back cylinder cock must get by the piston packing or by-pass or starting valve. Now put reverse lever ahead and try the other indicator plug or cylinder cock. If a leaky by-pass valve in the front end is the trouble, no steam will come through. To test the low-pressure piston packing, place the engine in the same position, lever in position to admit steam into the front end of high-pressure cylinder. Open starting valve, remove back indicator plug of low-pressure cylinder and give engine steam; if steam comes from the indicator plug opening or open back cylinder cock, either packing or by-pass is leaking. To determine which one, put reverse lever in another position, close back indicator plug and open forward one; if blow still continues, the packing rings are leaking or else both by-pass valves. Would then inspect the by-pass valves.
29. Q. How can the blow through sleeve packing between high and low-pressure cylinder of the tandem compound be located?
A. Place the engine as before on the top quarter, put reverse lever in forward gear, see that starting valve is closed, block the drivers or set the brakes solid and open the throttle. Until the engine moves, unless there is a leak, no steam can get into the front side of the low-pressure cylinder. Remove the indicator plug in front end of the low-pressure cylinder for this test.
30. Q. How test for piston packing blow with balanced compound?
A. For a Baldwin balanced compound to test the high-pressure piston packing, place the engine with the outside main pin on that side of the engine on the bottom quarter, the reverse lever in the forward notch, starting valve closed, set the brakes solid or block the drivers, remove the indicator plug in the front end of either the high or low-pressure cylinder. With throttle open this will admit steam to the back end of high-pressure cylinder. Steam coming out of this plug opening, will indicate a leak past the piston or the high-pressure valve. If uncertain, next test the high-pressure valve by moving the reverse lever to the center notch. This should cover the ports and if the valve is tight the blow will stop. To test the low-pressure piston, place the engine in the same position with wheels blocked, starting valve open, back indicator plug out; when throttle is opened, the leaky packing will be shown by steam issuing from the plug opening. If uncertain, the valve can be tested by bringing reverse lever to the center of quadrant, which will spot valve over port and if it is tight the blow will stop. In any compound engine a blow past the high-pressure packing tends to increase the pressure in the low-pressure cylinder. A blow past the low-pressure packing can always be heard at the exhaust, and is usually on both forward and back strokes, while a blow past the by-pass valves or valve bushings occurs at a certain part of a complete revolution only.
31. Q. In case it was necessary to disconnect on one side of a compound engine, how would you cover ports and hold valves in position?
A. The easiest way is to clamp the valve stem to hold valve in mid position; this should cover all ports. It may be necessary to take off head of piston valve chest and block in there.
32. Q. Is it a disadvantage to work a compound engine in short cut-off? Why?
A. Yes. If cut-off is too short the proper proportion of steam passing the throttle will not get to the low-pressure cylinder. The work should be divided between the two cylinders on same side.
33. Q. In what way do the Mallet or articulated compounds differ from other steam locomotives in the distribution of the steam?
A. Mallet compounds have two separate and complete engines under one boiler. The rear engine has a rigid connection to the back end of the boiler; this engine works boiler steam direct the same as a simple locomotive. Under the front end of the boiler is another engine so constructed that the entire front engine can move from side to side under the boiler, having a hinged connection at the front end of the rear engine to allow the locomotive to pass curves more easily. The front engine takes the exhaust steam from the rear engine through a flexible pipe or receiver and works it through a larger set of cylinders and thus compounds the steam. From the low-pressure cylinders the steam is exhausted to the atmosphere through the stack.
34. Q. How do you get the use of both engines when starting a train?
A. To get steam into the low-pressure cylinders before the high-pressure engine has exhausted, some types of the Mallet compound have a live steam pipe with a valve in the cab to admit boiler steam to the receiver pipe and thus get the use of the front engine in starting a train. The American Locomotive Company articulated compounds have an intercepting valve similar to the one used in the Richmond cross compound, located between the exhaust passage of the rear engine and the flexible receiving pipe of the front one. This intercepting valve when in SIMPLE position, allows the high-pressure cylinders of the rear engine to exhaust directly to the stack instead of into the receiver, and feeds boiler steam at a reduced pressure into the receiver pipe for the low-pressure cylinders without giving any back pressure on the high-pressure pistons. This increases the power of the complete locomotive about 20 per cent. When in compound position, the intercepting valve cuts off the supply of live steam to the receiver pipe and forces the exhaust steam to go to the low-pressure engine ahead.
35. Q. How is the American articulated compound changed from compound to simple, and back to compound again?
A. To work the locomotive simple, place the handle of operating valve in the cab to point toward the rear. This admits steam against the piston that operates the emergency exhaust valve and opens it. Exhaust steam from the high-pressure engine can pass to the exhaust nozzle instead of to the low-pressure engine. The intercepting valve then moves over so that live steam reduced to 40 per cent. of boiler pressure goes through the receiver pipe to the low-pressure engine. To work compound, place the handle of the operating valve to point forward. This will exhaust the steam, holding the emergency exhaust valve open; a spring and the pressure of the steam exhausted from the rear engine will close the emergency exhaust valve and build up a pressure against the intercepting valve that will open it so exhaust steam from the rear engine will go to the forward one and at the same movement close the reducing valve so no more live steam goes to the receiver.
36. Q. When is it necessary to use the operating valve to change the locomotive from compound to simple, or from simple to compound?
A. When giving the engines steam to start, the intercepting valve should automatically go to simple position until exhaust steam from the rear engine builds up a receiver pressure that shifts the valve to compound; if it does not, use the operating valve. When moving less than four miles an hour or when about to stall on a grade, set the engines working simple; changing to compound when the danger of stalling is over or the speed is more than four miles an hour. If there is no intercepting valve to furnish live steam to the forward engine, open the starting valve to admit live steam to the receiver pipe and low-pressure engine.
37. Q. If in starting the locomotive the forward engine does not take steam, what is the trouble?
A. The reducing valve may be stuck shut on account of being dirty or stuck on the stem of the intercepting valve. In case the reducing valve is stuck shut, the head of the dash-pot can be taken off and the valve worked back and forth to loosen it. The intercepting valve should be liberally oiled just before starting and occasionally during long runs to keep it free from sticking.
38. Q. Why does the Mallet compound have more power when working simple than compound?
A. If a starting valve is used to admit live steam to the receiver pipe and thence to the low-pressure engine, this gives a higher pressure to the low-pressure cylinders. If an intercepting valve is used, the open emergency exhaust valve allows exhaust steam from the rear engine to go direct to the stack; this takes away the back pressure of the receiver steam from the high-pressure pistons, about 30 per cent. of the boiler pressure, and thus adds to the power of the rear engine. The reducing valve when feeding live steam gives about 40 per cent. of boiler pressure to the low-pressure engine instead of the 30 per cent. it gets from the receiver; the added power of both engines working simple is about 20 per cent. over the compound operation.
39. Q. What is the duty of the by-pass valves on the sides of the low-pressure cylinders? Should they be kept clean of gum and grit?
A. These valves are connected to the steam ports at each end of the cylinders and open to allow air and steam to pass from one end of the cylinder to the other; away from the moving piston when the engine is drifting. If not kept clean they may stick open; when working steam the engine will blow badly; if they stick shut the engine will pound when drifting.
40. Q. In what position should the reverse lever be when the steam is shut off and the engine drifting?
A. Below three-quarters of full gear, so the valves will have nearly full travel.
41. Q. Why should the power reversing gear of the Mallet compound always have its dash-pot cylinder full of oil?
A. To prevent the too rapid movement of the reverse gear piston and its damage.
42. Q. In what position should the engines stand to test for blows in valves and piston packing?
A. Put the operating valve, or starting valve, in simple position. Spot the engine in the proper position and test each engine for blows the same as for a simple engine.
43. Q. What power is used with Ragonnet or Baldwin power reverse gear?
A. Air pressure.
44. Q. Can and should steam pressure be used?
A. Yes. However, steam should never be used except in an emergency when air is not available.
45. Q. What precaution should be taken regarding steam check and throttle?
A. That they are tight and check working properly, to insure that steam is kept from entering main reservoir, for if it should do so it would burn out the gaskets in the air brake equipment, allow moisture to accumulate, which would result in freezing and bursting of equipment as well as being dangerous.
46. Q. What would cause the gear to fail to hold links in intended cut-off, and allow them to raise and lower without operating valve in the cab being changed?
A. Leaks in main valve and piston packing.