A. An Allen ported valve is an outside admission slide valve having an
extra port from one end of the valve to the other, above the exhaust
cavity and through the body of the valve. This extra port is calculated
to admit steam through the valve at the same time that steam passes by
the end of the valve into the same steam port, thus doubling the area of
opening for live steam when the port is first opened.
31. Q. What is the difference in the valve motion for outside admission
valves and for inside admission valves?
A. An outside admission valve must be moved in the opposite direction to
an inside admission valve in relation to the movement of the steam
piston when beginning its stroke; therefore either the position of the
eccentric or the position of the rocker arms in relation to the rocker
shaft must be opposite for a change in these valves.
32. Q. What is a direct motion valve gear? What is an indirect motion
valve gear?
A. A direct motion valve gear is one in which the valve moves in the
same direction as the eccentric rod, that is doing the work, in many
cases no rocker arm is used. In case a rocker arm is used, both arms
point in the same direction like the letter U. An indirect motion valve
gear is one in which the valve moves in an opposite direction to the
eccentric rod doing the work. A rocker is used in which the arms point
in opposite directions from the shaft connecting them. Owing to the
design and construction of the Walschaert valve gear, it is a direct
motion gear when the engine is running in one direction with the link
block in the bottom of the link, an indirect motion when the engine is
running in an opposite direction with the link block in the top of the
link; usually direct motion when running forward.
33. Q. How can you detect the difference between a blow in valve or
piston packing?
A. A blow from the valve is more constant and has a somewhat different
sound, while a blow from cylinder or piston packing will blow stronger
at the beginning of the stroke and gradually decrease as the stroke is
completed.
34. Q. How would you place engine to locate broken admission steam ring
in piston valve?
A. Would place engine on quarter, reverse lever in center so as to cover
ports, then open throttle; and the steam will blow out of cylinder cock
at the end of cylinder where broken valve ring is located.