The percussion beater pneumatics in European organs pneumatics have
valves and associated pouches that are plenty large enough to provide
very quick action -- both in filling the pneumatic with air and in
releasing it to play the instrument.  If everything is working right
and the punchings in the music books are placed correctly, timing isn't
an issue.

Beater and pneumatic travel are usually limited by a rest bracket and
are not meant to be adjustable without modifying the mechanism.  The
adjustment, if necessary, comes in balancing the spring tension to the
air pressure.  Too much spring tension, and the pneumatic won't open
fully, causing it to lose power due to diminished playing stroke.  Too
little, and the spring itself will have too little force to play
loudly.

Vacuum operation in later German organs and most American organs
provided a higher differential between vacuum and atmospheric pressure
(up to 20" water column) than in a pressure operated organ (usually
less than 10").  This higher differential provided enough power to
enable vacuum-operated reiterating snare drum pneumatics to be used.

However, the bass drum in most of these organs still worked on pressure
inflate, spring deflate-to-play because of faster response.  (Many, if
not all, North Tonawanda organs are an exception, with a vacuum-operated
bass drum mechanism).  The huge dump/reinflate valve in the bass drum
action is generally "played" by a powerful medium-size pneumatic that
responds to the main valve chest.  A slight advance in the cardboard
books (European) or in the tracker bar (Wurlitzer) enables correct
response time.

Art Reblitz

 [ David Wasson's concert fairground organ, "Trudy", has a vacuum
 [ powered bass drum beater.  The pneumatic is rather small, the
 [ valve is triple, and a reservior is adjacent to the big valve
 [ block.  It operates so quickly that no compensating advance is
 [ needed in the music roll or the tracker bar.  -- Robbie