Electric valves
By Robbie Rhodes
John Rhodes works at the Hewlett-Packard plant in Vancouver, Washington, and wrote me:
> We have considerable expertise here in small, high-frequency
> magnetic relay designs. This division of H-P built a line
> of impact printers with scanning 24-wire heads. When we
> abandoned the product line about 7 years ago we had an excellent
> understanding of the physics and fabrication technologies needed
> to make 3 kHz (!) heads. The principal design engineer is a good
> friend and still works at this division. I'd enjoy looking at
> samples of various piano valves, and make suggestions on how to
> improve the designs.
Here are the "top level" requirements, John.
The finished assembly of valves (the "valve box") will typically be installed underneath the grand piano, in close proximity to the pneumatic action stack in order to minimize the length of connecting hoses. One hundred (100) valves are needed to control Ampico pianos, including the Motor Shutoff logic, while permitting normal operation with a music roll. A long, thin valve, with its exit bore along the long axis, would permit arranging the valves and hoses compactly.
The valve must open a port of about 0.090-inch diameter. There must be no leakage, which is a problem especially at minimum suction ( 4 inches-water vacuum). The highest sustained vacuum is 40 inches- water (Ampico B). DuoArt pianos may require "short-term" operation at 70 inches-vacuum, and the dc supply voltage will temporarily be increased proportionately.
The repetition rate required is 25 cycles per second at 75% duty-cycle. Pianos with 2-stage valves, such as the Ampico A, can respond to this machine-gun frequency!
Noise and power dissipation must be minimal. Assume a 15-volt power supply for operation at 40 inches-vacuum. A coil of 150 ohms resistance will dissipate 1.5 watts. Up to 33 valves may be "on" at once, therefore the valve box must dissipate 50 watts maximum; this should not require a fan.
In modest quantities (1000 units) we would like the cost to be less than $4 per unit.
-- Robbie Rhodes
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(Message sent Thu 4 Jan 1996, 04:41:47 GMT, from time zone GMT-0800.) |
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