Pete has one of those problems that pneumatics won't fix.  When the piano
plays too loud on loud passages but soft on soft passages, that just
means one thing: His valves are leaking.  Probably due to shrunken
pouches or maladjusted lifter buttons.

What happens here is that the player on low vacuum leaks badly because
the tension in the stack isn't enough to "suck down" all of the valves
tightly.  So he raises the first intensity enough to tighten the stack
valves.  After that, it plays the first intensity just fine.  But since
the first intensity has been raised too high, it boosts everything
exponentially after that, and by the time his piano reaches mezzo-forte,
it's peeling the wallpaper off the walls.

Craig B.