Purpose of Ampico A Slow Crescendo Spring

by Craig Brougher

This comment is in reference to a posting from Robert Taylor which appeared in the Mechanical Music Digest on February 19, 2003.

Robert Taylor's explanation of the reason for a crescendo pouch spring explanation is not quite on track, and confusing to those trying to understand how the Ampico mechanism works. The pouch spring in an Ampico A slow crescendo valve is not to guard against air leakage at the edge of a roll, as claimed. If there were air leaks at the roll's edge, as compared to the center of the roll, for example, the valve would activate, spring, or no spring, slot or no slot. Valves are go-no go devices. marginal leaks therefore cannot be tolerated, period. And they certainly were not planned for with springs, weighted to desensitize the valves to small leaks. That's all imaginary, unproven theorizing,. given as an established fact.

Besides, in Ampico model B rolls (which all model A Ampicos must also play), there is another hole even closer to the edge of the paper than the slow crescendo hole, and if there were air leakage by nature at all roll edges as Bob Taylor insists, then I guess that means the amplifier hole and the sub-intensity hole would be always on the brink of being "on" all the time, due to their even closer proximity to the edge. Talk about losing your expression! Man, it would be 'way gone. But then, according to Bob, one might suppose that's why they put the amplifier hole at the far edge of the paper-- so that it could leak "naturally" all the time, like those holes always do at the edges (?) Obviously if one believes this, then one also believes that Ampico didn't know much about player pianos. It's got to be either Bob's error or Ampico's.

The purpose of the spring is very simple: The crescendo unit is always mounted upside-down in grands. The valve itself is extremely light with a very tiny 9/64ths valve hole. The stem is matchstick-size. All valves rely on the vacuum to return the poppet against the pouch, and the vacuumed weight on such a tiny poppet is marginal anyway, so they added the helper pouch spring to that one, since it is the one with the muffler tube. The muffler tube slows the poppet's return impulse just a bit more than the fast crescendo spring without the added resistance. It collapses the pouch as air is bled back out from under it, speeding up the valve's return.

As far as the weighted primary valves of the B, that's for a different reason. The B valves are not "outside valves" or so-called "primaries" at all. They are poppet valves. That means, they require either weight or a spring to tightly seal a pallet hole that's not centered in the axis line of the valve. That kind of a valve is vacuum operated pallet valve-- a different sort of valve altogether.

Regarding proximity leakage of roll paper. The very basis of player pianos to begin with, and the very reason they work is because the holes seal off air tight, even when you have two holes open side-by-side with only a few thousandths web of paper separating them. On some very tiny trackerbar scales like residence organs, this web of paper can be only .015-.020 wide. That's a "fur piece" from the margins Ampico allowed for the slow crescendos.

Craig Brougher

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This page was last revised on March 11, 2019

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