Assist assistance needed

[Phil and Judy Rose <pjrose@servtech.com>]

OK, I admitted my ignorance in regard to brake assist, but no one's come
forward yet to offer enlightenment. Hence, some more questions:

(1) How many psi (from the N2 bomb system) are necessary to provide assist?
I gather from what I've read that there usually is enough "stored" for
about 30 pedals worth. So what's that amount to, 30x10 psi or 30x100 psi or
what?

(2) As an aside, how _does_ vacuum assist work? Not many psi of vacuum are
available from the manifold, so how is this translated into positive
assist? Must be a _big_ membrane involved.

Back to the bomb:
Whatever assist the bomb stores (need answer to question #1 here) for Total
Assist Potential (Pa) we can assume that it is accomplished by the membrane
being deformed to the extent of reducing initial gas volume in direct
proportion.
[Recall the Gas Law: PV = constant]
So, if Po is 2000 psi, then Pa = +300 psi (of TAP) comes from just a 15%
reduction in gas volume (=Pa/Po). This needs fairly little displacement of
the membrane--assuming a hemispherical geometry. This small movement would
permit the membrane to be a pretty rigid thing. High rigidity would also
limit the distortion of the membrane (which I assume is a good thing) when
the bomb is stored empty. This makes me wonder:

(3) Could "bomb failure" could be caused--rather than by gas loss--by
membrane aging? This kind of change over time might _increase_ membrane
rigidity beyond the hydraulic pump's capability of to deform it
sufficiently.

An admittedly off-the-wall conjecture, but, if true, it would make gas
recharging a non-issue. So is it possible that gas pressure loss--although
plausible--is merely anectdotal? Do we have specific info from Audi (or
others) on the known mode(s) of bomb failure?

Phil Rose

Nature is doing _me_ in by hardening my membranes, why not my Audi's?

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