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.