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MMD > Archives > February 2010 > 2010.02.27 > 06Prev  Next

Rotary Pump Problems in Welte Licensee Upright
By Jonathan Holmes

I have been working on a Welte Licensee (rare in the UK) in a British
Waddington upright piano.  I have rebuilt and re-leathered the primary
and secondary valves and replaced all the gaskets.  I have also rebuilt
the expression system.

The instrument came into my workshop with some things done, but very
badly, but it played of a sort, but now after the rebuild, _nothing!_
I am quite confident -- well, as much as bench testing can give me --
that the stack is okay, but when the pump is switched on, nothing
happens.  The roll motor works but there does not seem to be very much
suction coming out of the pipes that go to the stack.

I have now blocked those off and the hose to the roll motor and the
pump still keeps going and does not show any strain.  I can hear a few
little hissing noises but, in my view, nothing really that much or
anything that would account for the problem.

The rotary pump had been recovered but it did need recovering again and
so I used the thickish maroon bellows cloth and replaced all the flap
valves.  The connecting straps have also been replaced but I wonder now
if that material is not strong enough?  But the bellows do seem to
open and closed.

When running the pump it seems that the pump is working but just not
moving or providing the volume of air that it should.  I may be wrong,
but the above test i.e. all the tubes blocked and it still runs makes me
_very_ suspicious.

Is the cloth on the bellows too tight, e.g., not enough or too much
span?  Are the connectors weak or are they too short or too long?
If I block off the outlet on the side of the pump after a turn or so
by hand it seems to lock up, but that is turning by hand.

I have tried tubing only the treble up so it could play just that
half.  Yes, you guessed right -- no music, not even a quivering hammer.
Where else should I look or investigate?  I plan to take the motor and
pump out of the piano and run further tests on the workbench.

Can anybody help or point me in the right direction?  I have rebuilt
such pumps in Duo-Arts before and other bigger pumps in German machines,
but this is a total mystery to me.  I think I am loosing it!

I realise over in the USA these instruments are commonplace but they
are very rare in the UK.  Please help if you can.

Jonathan Holmes
Penzance, UK

(Message sent Sat 27 Feb 2010, 16:17:48 GMT, from time zone GMT-0500.)

Key Words in Subject:  Licensee, Problems, Pump, Rotary, Upright, Welte

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