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.