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MMD > Archives > December 1997 > 1997.12.07 > 15Prev  Next


Rebuilding Simplex Pneumatics
By Craig Brougher

Roger Waring was asking why, after he followed every word in the
Reblitz book on Rebuilding a Simplex Player piano, it was still leaking
somehow.

That's the way it always is, with any book, unless you also learn all
the little principles as you go along that would make the statements
fully true or partly true.  So much has to go unstated, and it's hoped
that you can pick up the idea from the overall text, along with some
details that you might miss, otherwise.  In the interest of time, he
has provided many pictures, instead.

There are several places Simplexes tend to leak in their stacks.
First and foremost is the big edge gasket.  Seal this temporarily with
masking tape and use the principle of the leakage tester I show in my
book.  If it leaks about the equivalent of two 3/32" holes at 10" of
vacuum, you are about right for a perfect Simplex.  If it leaks like
four 3/32" holes, you will definitely feel it in your pedals with the
air motor paused.

Other places to look are:

2. A number of slightly "cocked" unit pneumatics which are not sealing
quite well enough.  Cure: Get some Dow Corning 111 Silicone grease,
coat them well, avoid the bleed hole, and don't trust the screws to
pull them tight!  Align them with the screws in, and keep them pressed
firmly while tightening the screws evenly.

3. The valves in the unit pneumatics.  When you replace the pouch
leather valve covers, the grain in the leather prevents the valve from
sealing off tightly.  (I'd be surprised if Art didn't mention this,
though) So what you have to do when you seat the valves is to "crush
them hard" (don't overdo it) down on their inside valve seats.  You are
trying to make an impression into the leather.  You can probably still
do this through the valve's top hole.  However, you may have another
problem that you can't take care of this way.

4. Leaky pouch leather valve seats.  Modern day pouch leather is no
longer "staked" and worked at the tanners for strength and tightness.
Nor is it made from registered herds of Scottish sheep bred for the
purpose!  So it is NOT the same stuff, anymore.  You should always seal
the pouch skin BEFORE you ever cut out those valves in the first place.
But try these other things, first.  Then if your stack still leaks, you
may have no choice but to get it right-- the second time.

5. Underpunching off-center.  The underpunching that centers the valve
in the inside valve seat hole is placed under the bottom leather,
between the wood and the new leather.  If this has been replaced and is
either not the right diameter, or a few of them are off-center, or, if
they were not replaced at all and are now either dry and leaky, or the
rubber face was scraped off, then your valves will have to be rebuilt.

That was the "Simple" part about the Simplex!  That's why the valves
sealed off.  One little "squirm" to seat, and they were down tight
again.  To the valve seat, it looks like a little "cork" because the
valve isn't just sitting on top of the face.  It is actually bearing
against the inside top edge of the valve hole, which makes for an
appropriately tight seal.

My question to you is, "How do you know for sure it is the stack?
Did you test it first before replacing it?" Could it be something else,
like the inside flaps in the pumps?

Craig Brougher


(Message sent Sun 7 Dec 1997, 14:38:01 GMT, from time zone GMT.)

Key Words in Subject:  Pneumatics, Rebuilding, Simplex

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