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MMD > Archives > June 1996 > 1996.06.14 > 02Prev  Next

Duo-Art "Grasshopper" Pump
By Craig Brougher

Pat Mullarky mentioned that his D/A "exposed" pump was noisy. That is a late model pump, but wasn't a "cheap" version, and would make just as much noise if it were boxed up. For gosh sake, don't replace it with a suction box! A Duo-Art would be too loud, even if you could completely silence the suction box. In D/A music, everything is controlled "blindly" by the roll, based on the capacity and characteristics of the instrument, and this revolves around the pump. Concert grands played louder, simply to take advantage of the large piano and the large hall, so they could run the pump faster and get away with it. However, that only perhaps added 50% or so to the power. A suction box would probably provide an order of magnitude more volume of air, but the closed head pressure could not get up to concert pressures like the D/A positive displacement pump can.

There are a lot of reasons those pumps can get noisy, but usually it is caused by the linkage and the crank bushings. You have to be sure they are true and tight, but rotate freely, and I suggest using JAX MagnaPlate 5 spray can grease on the rod ends. The original grease is no longer available. It was modelT wheel axle grease which was loaded with graphite. You can't even find long fiber grease anymore.

Another cause of noise is failure to replace the flap valves and seats, and to make sure the flap springs are pulled. If you have a partially dry-rotted flap seat ciphering twice as much as another one, then you have a dynamic imbalance which causes the wheel to speed up and slow down. That makes a thumping noise.

Craig B.

(Message sent Fri 14 Jun 1996, 12:52:23 GMT, from time zone GMT.)

Key Words in Subject:  Duo-Art, Grasshopper, Pump

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