Here are some pictures of a
reversing/throttling steam valve that controls a drum winch, like for a
marine railway. The handle will rotate about 45 deg with the
center being off or closed.
The seemingly apparent problem with this is
the D-valve would try to unseat itself in reverse. This is taken
care of in a few different ways. One is the valve is captive on the
seat by the steam box cover. Not a very good way, but
effective. Another way is to hold the D valve in place by a balance
disc on the back of the valve. Both of these ways are effective, but
not very efficient. Obviously, with a piston valve this type of
reversing valve arrangement works much better.
slippers are held out from the stem by a spring in the center to keep them
in contact and seated with the bore of the valve. The interior
'cavities' of the slippers are the low pressure sections, or exhaust,
which also forces the slippers against their seats.
exhaust is from the bottom of the valve body.
is a Gies Reversing gear. They were found in marine use quite
often. The design is still popular today for industrial reversing