Gordon,
Over pressure and under pressure is actually a small differential
more than that and it can cause damage.
The basic mechanism has two factors management and reliability of
the system.? The latter has to insure there are no hard transients
or misses.
The older way was the box with the head out, iron lung, though the box
could easily be plywood glued up.? A variable displacement bellows d
id the work with a motor.
Allison
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