steam leaking into the cylinders can come from a leaky throttle or leaky
dry pipe.

79. Q. Is it possible to distinguish between a leaky throttle and a
leaky dry pipe?

A. Yes; a leaky throttle usually leaks steam at all times. A leaky dry
pipe will leak both steam and water. It will show a stream of water at
the cylinder cocks when the water level in the boiler is raised above
the leak in the dry pipe.

80. Q. What effect have leaky steam pipes in the smoke-arch, and how
should they be tested?

A. Leaky steam pipes waste steam and very seriously affect the draft in
the front end. A bad leak in the back part of the joint at the bottom
will blow into the tubes and make the engine smoke at the door with
throttle wide open while standing still. To test them, open the front
door and cover the joint with fine cinders. When the engine is given
steam, the cinders will blow away from the leak; to properly test them
in the shop, water under heavy pressure should be used.

81. Q. How should the test for a leaky exhaust pipe joint, or a leaky
nozzle joint be made?

A. About the only test that can be made on the road is to open the front
end and reverse the engine with throttle partly opened, watching the
suspected joint at the same time. For the bottom one with cinders around
the joint, for the top one it can sometimes be detected by holding a
torch near the joint.