nearly equalized. This is done by protecting a portion of the top of the
valve from the steam pressure. It is usually balanced by strips held
against the pressure or balance plate by one or more springs. This is
done to prevent live steam from getting on top of valve and thus relieve
the valve from the top pressure which would cause excessive friction
between the bottom of the valve and its seat. The hole through the top
is to allow any steam which might leak by the strips to pass into the
exhaust, so pressure could not accumulate on the top of the valve, also
to equalize the exhaust pressure between the top of the valve and
exhaust cavity as well as to assist in lubricating the balance plate.

28. Q. What is meant by inside and outside admission valves?

A. With an inside admission valve (usually a piston valve), the live
steam comes between the piston valve heads, the outside end of the heads
being connected with and exposed to exhaust pressure, it admits steam
past the inside edges of the valves. An outside admission valve has the
space between the ends connected to the exhaust and a space at the ends
connected with the live steam. It admits steam past its outside edges. A
piston valve can be either inside or outside admission, while a slide
valve is always outside admission.

29. Q. What is the relative motion of the main piston and the steam
valves for inside admission, and, on the other hand, for outside
admission?

A. If the piston is in the front end of the cylinder, an inside
admission valve must move forward in order to connect the inside of the
valve with the front live steam port to admit steam against the piston.
The outside end of the valve opens the exhaust port for the back end of
the cylinder. In the same position of the piston an outside admission
valve must move backwards to open the steam port or in the same
direction as the steam piston when commencing its stroke.

30. Q. What is an Allen ported valve, and what is its object?

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 a