re: Bomb Gas Pressures

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

>Date: Tue, 2 Dec 1997 00:01:05 -0800 (PST)
>From: Orin Eman <orin@WOLFENET.com>
>Subject: Bomb Gas Pressures
>
>OK, so here are the N2 pressures for the bomb, courtesy Mr Bentley:
>
>New bomb:  78 - 82 bar (1131-1189 psi).  I'll take that as 80 bar +/- 2.
>
>Minimum:   30 bar (435 psi)
>
>both at 20C/68F.
>
>The pressure relief valve in the bomb opens at 150 bar (2175 psi),
>so the pressure ratio is actually a little less than 2:1 (150:80)
>for a new bomb, 5:1 for a nearly dead bomb.
>
>Orin.

OK. Then the loss of pressure at the defined "dead" point comes to about 50
bar, or more than 1/2 the original amount of nitrogen. If gas loss is by
natural permeation through the membrane and is more-or-less constant over
time, and if the MTBF is assumed to be what, um 5 years, 6 years? Let's say
6 years. Then the monthly pressure loss works out as about 10 psi. Of
course the loss of nitrogen isn't going to be linear at all; it will depend
on the gas's partial pressure _differential_ (inside/outside), so that it
should lose nitrogen at a much faster rate in the first few years compared
to later on. Seems that if the manufacturer would ship these buggers
pressurized on _both_ sides (I assume they're _not_), shelf life wouldn't
be much of an issue. Might not be too practical for ease of installation
though.

Thinking about all this makes me wonder why Audi didn't design the
hydraulic system to relieve the (hydr) pressure in the bomb when the
ignition switch is turned off? Is this supposed to be a safety feature for
the truly neurotic? Seems to me that the long periods that the bomb spends
with high hydraulic pressure applied (while car parked and engine off) is
time that it's losing nitrogen at a faster rate than otherwise would be. Is
this, as we pidgin-Deutsch speakers might say:

"Ausdunstung Durch Technik"?

Phil

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