I have recently acquired a Hupfeld Upright and would like to know if
there is any special regulating technique necessary for the wind motor.

The lower action arrangement comprises a control pneumatic tensioned
in the open position by a fixed 6-inch "Y" spring, the type usually
found on pedal exhausters, rather than an adjustable coil spring.  It
appears non-adjustable.  I have replaced the rather weak original "Y"
spring with a new one from PPCo.

An external 1-inch diameter threaded wooden wheel allows some
regulation by limiting the maximum operating span of the pneumatic.
From trial and error, it seems that restricting the span speeds up
the motor and opening it slows it down.  I have now got to a point
where performance is adequate, but not perfect.

The problem is that no setting seems to completely prevent a
slight increase in tempo when pumping hard.  Is there some other
variable element that I have missed or is it just a case of further
experimentation?  I have to say that the motor performs very well when
pumping softly.  Should I revert to the weaker spring?

The new one is considerably stronger and requires quite a lot of
suction to close it, whereas the original closed very easily and was
more inclined to slow down and even stop on hard pumping.  All replies
acknowledged.  Many thanks.

Roger Waring