Having read of Doug Vensel's plight in MMD 150814, I offer the
following observations and suggestions.  The valves look to be
identical, or at least very similar to "Standard Action" 2-tier
valves.

The first metric I would like to know is, with the tracker holes
covered and the air motor at Tempo 0, is it possible to pump to the
point that it is difficult to pump any more?  Or more precisely,
what is the maximum chest vacuum that can be achieved (inches of
water column) and how many pedal strokes per minute does it take
to maintain that level?  Is there a spill valve in the pumping
stream and does it actually ever spill?

Secondly, Doug mentions having tested each valve with a "bubbler
bottle".  I would like to see a photo of exactly how and where he
positioned the apparatus connecting with the bottle, and what were
the results, i.e., bubbles per second, using what fluid in the
bottle (water? oil?).

Next, I would observe that, at least in my experience, Standard
Action type valves almost _never_ need to have the valve facing
contacting the internal vacuum plenum replaced, but if they are,
a hard-tanned (smooth) leather should be used because it will "slide"
more easily on the metal seat and find its best sealing position.

Part and parcel of this sealing ability is the "wobble" that Doug
mentions, which is very difficult to set with consistency because it's
a function of the force-fit collars on the stems.  My guess is that
these collars are now too tight and the lessened wobble combined with
a leather face with too much "tooth" is frustrating efficient seating.

If at all possible I would go back to the original hard, slick facings
if you still have them or select a leather with the same surface
characteristics.  If you are going to retain the new, coarser leather,
spraying the metal seats with an aerosol such as "Permalon" could be
helpful in promoting "sliding".  (Permalon is basically a spray form
of Teflon and is also useful for air motor sliders, knife valves and
the like.)

The bubble jar test cannot differentiate between leakage due to poor
face/seat contact and leakage around the stem.  Suffice it to say that
leakage at the stem will likely be a very small percentage of that of
the face/seat contact simply because of the difference in surface areas
of the two components.

If stem leakage is suspected, a _minute_ bead of PVC-E glue, applied
top and bottom with a hypodermic-type applicator, but not enough to
inhibit the wobble to any degree, will take care of it.  The bulk of
the leakage will likely be at the face/seat contact point due to
inadequate wobble, so this is where the most attention should be paid.

The bubbler test likewise cannot differentiate the portion of the
leakage from poor contact of the metal plate with the plenum chest.
Even though there is a blotter paper gasket at this contact point,
I normally add a bead of PVC-E (thinned about 50% with water) to the
periphery of the metal seat.  This proportion of PVC-E to water does
not normally present a removal problem should a valve need to come out
for re-work.

A poppet travel of 0.055" seems a little generous to me, but since
the pneumatics are a bit smaller than in a 3-tier system (dimensions?),
a somewhat higher vacuum may be needed to give the pneumatic enough
"oomph".  I would split the difference between this and a widely
accepted valve travel of 0.035" and make them 0.045".

As far as repetition goes, this can suffer from either overly leaky
pouches or blocked bleeds, or a combination of both.  If the pouches
have peen replaced in the process, they probably need to be sealed.
I have my favorite substance for this but will decline to mention it
in order to avoid getting into any arguments.

Suffice it to say, newly replaced pouches that have otherwise been
untreated _must_ be sealed.  Cleaning/unblocking of bleeds should be
obvious and straight-forward.  Swabbing the inside surface of the valve
well with the aforementioned 50% thinned PVC-E never hurts either.

Good luck and let us know how things go.

John Grant