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MMD > Archives > February 1998 > 1998.02.04 > 15Prev  Next

Decap Wind Pressure
By Hans van Oost

Mr. Robert A. Oppenheim wrote to MMD 980131:

> ... We have a 72 key Decap purchased several years ago as an almost
> basket case.  Any idea as to what pressure it should be operating
> at?  Also, the same question regarding the accordion.  The accordion
> always seemed to be overblown so I constructed a small regulator to
> reduce the pressure to it.  That has been a big help, but there are
> still some strange things going on.  I have not attempted to tune
> the pipes as I am not sure of the pressure.  Anyone out there have
> any ideas?...

I have checked with several people who have worked on Decap organs. The
mean value they give for wind pressure of the pipes is 200 mm (7.87
inches) Water Column, but the answers vary between 180 and 220 mm (7 to
8.7 in.). I think the last value is rather high for an instrument that
is supposed to play inside a cafe or dance-hall, for which they were
designed.  This pressure refers only to the organ pipes and the

The accordion(s) play on a different, and lower, pressure. Some organs
(after 1935) had a crescendo and decrescendo device built in. Does your
organ still have such a machine?

If you can tell me what other strange things are going on I could
possibly be of some help.


Hans van Oost
E-mail: (leave out the last word)

(Message sent Wed 4 Feb 1998, 22:24:23 GMT, from time zone GMT.)

Key Words in Subject:  Decap, Pressure, Wind

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