[urq] Pressure Accumulator substitution

[urq]

... you still have highly pressurized gas on the back side of the membrane.
I'm by no means an expert, but I'd think what you'd need to do to minimize
(stop) the diffusion would be to pressurize the open side of the membrane
with nitrogen at the same pressure as the back side ... not too likely the
manufacturer would do that.  Hydraulic fluid, air, whatever at atmospheric
pressure is not likely to make any difference in the diffusion of the
nitrogen through the membrane when it is on the shelf.  Pressure
accumulators would not be the only part in the inventory which has a shelf
life.  It isn't as though they'd go bad in anything shorter than a couple
years from sitting on the shelf.  

When the bomb is installed and everything is operating normally the
accumulator will almost always be pressurized to a pressure higher than the
pressure that the accumulator sees on the shelf.  Interesting thought that
the pressures on both sides of the diaphragm will be equalized, maybe the
amount of diffusion will be reduced ... my thinking is that the pressure
exerted on the nitrogen is higher, and there's no nitrogen on the other side
of the diaphragm ... that's why my gut feeling is that it will deplete the
reservoir faster.  In the case of an older car which has a leaking brake
servo that depletes the pressure in the system when the car is shut down,
and where the car isn't operated regularly, you'd see lifetimes about the
same as the shelf life ... 

Steve B
San Jose, CA (USA)

-----Original Message-----

However, the ATF fluid in contact on the other side of the membrane is at
equal pressure (36-57 bar), and might "seal" the thing better than air from
atmospheric pressure.

That being said, if there was a problem sitting on the shelf, IMO the
manufacturer would have installed a sealed cap to prevent this behavior, an
easy and cheap preventive measure. And there would be a notice to 'splain
the stocking procedure. In an ideal world, at least :-).

Louis-Alain

-----Message d'origine-----
Yes, they can go bad on the shelf.  The problem is that the pressurized gas
leaks through the membrane over time.  That said, having one unpressurized
on the shelf will last longer than a functional one in a car, where it
should normally be sitting at higher pressure pretty much constantly ... 

Steve B
San Jose, CA (USA)