Duo-Art "Grasshopper" Pump
By Spencer Chase
|Patrick Mullarky writes:|
> The Aeolian Duo-Art has a very strange pump: a four-lobed exposed
> bellows pump with the crankshaft running along the top. I would guess
> that it is a smaller version of the "Steamboat" six-lobed pump. I would
> really like to replace the pump with a quieter box pump and motor...any
> leads??? (Would that be too much of an "alteration"?) I've rebuilt the
> pump bellows, but it huffs and puffs a bit as it runs...and you can
> hear the valves slap under load. I have a hunch this piano was in the
> "entry-level" price-range, hence the noisier, cheaper pump. I believe
> that box pumps were the norm in 1922- era reproducers.
I just finished rebuilding a similar pump from a Stroud upright. It was a real challenge. The thing is the cheapest pump Aeolian ever used and I was about to give up trying to make it quiet. I really did want to keep the piano original but I had to add a few improvement to the pump or scrap it altogether. The problem is that having only four small feeders requires that the thing run as fast as a box pump, but with all the cheap undersized noisy parts exposed. In addition the thing is screwed right to the case of the piano so any sound it makes is amplified. The following modifications made it quite acceptable although not "factory original." The slapping noise is probably not just the flap valves but the pneumatic cloth popping when the feeders try to exhaust air too rapidly for the small valve openings. I used a fairly heavy leather (well sealed) added a little extra width and adjusted the connecting rod length (made new ones several times) until the thing stopped slapping. I made the rods out of a high density slippery plastic (scrap I don't know what it is) that looks just like ebony. The undersized soft iron crankshaft does not stay straight and causes wooden rods to squeek and clatter. There may be some wood that would work but I didn't find one. I carefully bored the original wooden main bearings out and replaced then with double ball bearings press fit into carriers which are clamped into the remaining wood with machine screws. This allows a lot of missalignment (unavoidable with the cheap crankshaft) without too much free play to cause clicking. If done carefully this modification can be barely visible when the pump is installed. The last modification was to add a bracket from the drivewheel side of the pump to the keybed. Originally the flimsy wooden pump was supported only at the non driven side and flopped around a lot. I wanted to keep the piano original but could not stand listening to all the clicking clattering thumping and slapping that was probably designed to sell a more expensive model. I would like to hear what others think of this sort of restoration heresy. If perfectly rebuilt to original specifications this pump would be unlikely to last a year without becomming noisy.
(Message sent Sat 15 Jun 1996, 07:50:27 GMT, from time zone GMT-0700.)