also a steam port for live steam from the boiler. As the pressure on
this valve is equal in both directions it is practically balanced.

27. Q. What is a balanced slide valve? How is it balanced, and why? For
what purpose is the hole drilled through the top of the valve?

A. One in which the steam pressure on the top and bottom of the valve is
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