I've just acquired a secondhand centrifugal fan to supply air to
a small pipe organ that I'm constructing.  I've coupled it directly
to a 1/4 hp electric motor that I already had; this is turning at
around 1500 rpm.

The fan has a 8-blade impeller around 8 inches diameter and an outlet
that is 2-1/4 x 3 inches.  The performance of the fan at 1500 rpm is
a little less than I would like.  It is giving only around 2 inches
of water gauge pressure.

My question is at what speed should this type of fan rotate to deliver
around 7 to 8 inches?  Perhaps some kind person might like to offer
advice please?

Best wishes to all from Australia

Michael J Taylor