Brett Mohr asked about the felt muffler over the Simplex pedal
valve. That, I believe, is called muffler felt and probably either
glued to a little frame, which in turn is screwed down to the valve
block, or possibly just glued or tacked directly. You can buy muffler
felt in different thicknesses from a pipe organ supply company, but for
a little piece like that, I wouldn't worry.  Build it up with a few
pieces of felt laid on top of each other, punch a circle of very small
holes through the stack and one to clear the valve stem, and tack it
down around the pedal valve with about 4 very small #1 tacks.

   However, a valve should not ever hiss, otherwise, it is leaking. The
only sound you should ever hear from a valve is a faint transit slurp
when its pneumatic relaxes. Hissing when actuated means either 1) the
pouch cannot raise the valve strongly enough, 2) there is a leak
between the outside valve seat and the pneumatic, 3) the valve is not
seating against the outside valve seat. These would not prevent the
pedal from working, necessarily, but the muffler felt described is
really more just to keep dirt out than to prevent noise.

   Just remember, any leak that hisses is a small one.

Craig B.