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?