The model B valves, when _correctly_ and fully restored, are by far the
most sensitive valves ever built. They are able to operate on 6 feet
of trackerbar tubing, directly from the trackerbar without primaries,
and are faster than the primary operating on the same length. This is
because the valve begins actuation on a (very precision) #70 bleed, and
drops on an equivalent (about) #56 bleed.
The inside valve return speed is quicker than a primary, actually,
because the vacuum pulling a primary down to its seat , versus the
upward force of a partially inflated pouch is a tiny bit less than for
an inside valve, whose valve well pressure aids the return just a bit.
So I know that both the speed or sensitivity of the ball bleed valve is
Dr. Hickman said in his diary that he was considering buying stock in
the Ampico Company on the strength of his ball bleed valve. The first
thing he did with them was remove the regular valve chests in the roll
cutting department and replaced all the old model valves with the new
ball bleed valves for production.
I have given an example of a good Ampico B playing a fast "A" roll
like Sawmill River Road, having lots of quick staccato played together
at low intensity, sometimes having been the top copy through the
perforator too -- which narrows the hole. The model B will play that
"marginal" copy when a good model A has to be "tweaked" to catch them
I would like to get it out of rebuilders' heads that the model B valve
is weak and slow. It is only weak and slow when you don't do good work
on them, when you don't replace their old, leaky ball bleeds, and you
don't replace their pouches, and then you don't set them for maximum
travel at lowest sensitivity (instead of thinking that you're going to
do it with a gap gauge). I've coached a number of other rebuilders
through a set, and hope that maybe they would give their observations
on this subject, too.
I also plan to have a video tape set sometime on the rebuilding of the
model B all the way through, from start to finish. We'll see, though.
I am presently restoring one. It's a cute single-legged white antiqued
Knabe of the Louis XVI style.
[ See Ampico's descriptions of the ball valve and other components at
[ -- Robbie