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