I assume Mr. Waring's problem is with an Autopiano with a Standard
single-valve action.  He asked how to narrow down the possible problem
with some simple tests.

First of all, the vacuum cleaner test with the upper deck off and the
pouch channel holes in the pouch board uncovered would be inconclusive,
since this tests all the valves together in the open position.  All the
pneumatics would be expected to operate together.  This says nothing
about the ability for the  valves to seat and hold in the closed
position.

First, remove the upper deck and put it aside.  Tape over the
pouch-well holes in the upper edge of the pouch board.  A standard
action should 'pull in' with the slightest amount of initial pumping.
In this mode, with the wind motor turned off, the player should pump up
quickly, and stay 'full' with only a few strokes a minute.

This test positively eliminates any problem with slight leakage in the
whole upper deck and tubing which might cause some valves to 'simmer';
but this seems unlikely from the problem you describe.

The inability of the action to 'pull up' immediately, is probably, as
you have concluded, either due to bad valve sealing or to the pouch
follower buttons screwed too far out.  Distinguishing between these two
problems is harder to do, because the external manifestations are the
same for both.

The next test is harder, but it does not involve working on the
individual valves at this time, so is worth the effort.

Remove the pouch board.  Put in every other screw, and hold the screws
from falling out with a bit of tape over the head.  Turn the board face
up, and put 2 washers, or a few thick center-rail punchings, on each
protruding screw.  Carefully put the board back on with a few screws
loosely in the unused holes, then loosely screw in the screws with the
washers.  The washer 'spacers' must be located all along the board, not
just at the ends, or the total force of the vacuum might bend the
board.

The idea here is to reassemble the pouch board onto the stack, but
placed an eighth of an inch or so farther out.  You might be able to
figure out an easier way to achieve this, depending on what spacer
material you may have.

Carefully tape over the crack on all 4 edges of the box, and also make
sure the pouch channel holes are taped over.  Also tape over all the
screw heads and unoccupied screw holes in the pouch board.

Now if the action 'pulls in' easily, the problem was the follower
buttons going too deeply into the pouch wells.  Poke a few holes in the
tape over the pouch channels; these notes may play weakly, or at least
partially open the valve and produce an audible hiss.

If the player still misbehaves as before, the problem lies with the
valves.

Even leaky, un-refaced Standard valves move easily and pull in quickly,
they just require far more frequent pumping to keep the vacuum up.  It
sounds more likely that there is mot enough flexibility at the joint
between the inner valve disk assembly and the stem on some of the
valves.  This prevents the valve disk from aligning itself easily to
the plane of the metal seat cup.  It only takes a few 'crooked' valve
disks to produce a big loss of vacuum.

If that is the case, here is the hard part.  You will have to take the
whole thing apart; remove the pneumatic decks and the finger-flange
board, hopefully in one piece.  After you reassemble the system with
only the valve board and the pouch board in the piano, you can locate
and mark the offending valves with an ear tube.

Please note that this is the way I would go about diagnosing this
problem.  I am looking forward to seeing the ideas of others, who
surely must know an easier way.

Richard Vance