Hi All,  I've received a number of responses to my inquiry [120113
MMDigest], and I'm somewhat surprised that the question wasn't answered
numerous decades ago.

I suppose I'm just as guilty as everyone else in that I have always
relied on the sensitivity of my 'touch' to "feel" if there was any
noticeable difference in the amount of force require to close a striker
pneumatic.  Two of the responses suggested that I construct a water
tube manometer to get an accurate reading.  So, after decades of
procrastinating because the device always looked cumbersome and
awkward, I finally made one!  Now, I wish I had made one years ago.
The results of the test are here (it took 3/4" of vacuum to collapse
the bellows 90+ percent): http://www.youtube.com/watch?v=JDwNDP5eSWU
 

Naturally, the quality of the bellows cloth has a lot to do with the
amount of force (vacuum level) that's required to close the bellows.
I have three different types of thin cloth in the shop, but the cloth
I used to build the test bellows was purchased from Player Piano
Company (PPCo) a month before Durrell passed.  (It is unfortunate that
that cloth is no longer available.)

As I demonstrate within the first three minutes of another YouTube
video ( http://www.youtube.com/watch?v=pXOfestZfZk
 ) I recently
completed, the hinge offers virtually no resistance to the movement
of the movable board prior to the cloth being glued in place.  In fact,
I try to show how the glue should be applied to help prevent getting
the glue on the 'exposed' area of the hinge when gluing the cloth to
the hinged-end of the bellow.  Naturally, if the glue gets on the
hinge, it will stiffen the hinge substantially.

Musically,
John A Tuttle
Player-Care.com
Brick, NJ, USA