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MMD > Archives > January 2016 > 2016.01.07 > 08Prev  Next


Suction Box Check Valve Problem
By David Dewey

Stan Morton wrote: "I recently removed the evacuator assembly from my
piano, with reservoir intact, and blocked off all ports, and the system
held vacuum for approximately 15 seconds before the reservoir was
depleted.  When reinstalled with all hoses reconnected, the reservoir
vacuum only lasts 4 to 5 seconds."

Stan, 15 seconds isn't very long (and 4 to 5 seconds is intolerable!),
and while it will pump a player, it will rapidly fatigue the pumper!
I would be much happier with something close to a minute.

If you have the ability, I would recover the exhauster reservoir (at
least) and make certain the flap valves are working properly.  You can
reconnect one hose at a time and measure the change in holding time to
find your "main" leak, although it does appear that the vacuum motor
check valve is very suspect.

As to the felt, it seems everyone had their own idea of what would keep
the box quieter.  If you have to tear the felt, you can replace it, but
you might want to try to use a putty knife to separate it from the
bottom board of the piano, instead of tearing it.

I've not had to repair a vacuum box flap valve yet, but I did run into
one player that had no check valve!  I over-thought the problem and made
a check valve out of some PVC fittings, a ping-pong ball and a piano
wire spring.  It works, but it's way over-built and takes up too much
space.  Good luck!  One does wonder how much work was done 22 years
ago, though.

I have had one instance of hearing that a player I rebuilt needs it
again.  In thinking it through, I rebuilt it in 1977, so the repair is
now 39 years old and the original build was about 55 years old, so maybe
it is time?!  Hmmm, this year is going to be our 40th anniversary;
I wonder what I'm going to have to repair!

David Dewey


(Message sent Thu 7 Jan 2016, 19:51:35 GMT, from time zone GMT-0800.)

Key Words in Subject:  Box, Check, Problem, Suction, Valve

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