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Re: CO2 systems, supersonic flow...

> From: Steve Pushak <teban at powersonic_bc.ca>
> Subject: CO2 valve characteristics at near empty tank
> 
> I do hope this is new information since I have not been
> monitoring the APD closely in recent months. We've had a recent addition
> to the family; young Dylan joined us three weeks ago.

	Congratulations!
> 
> The first point is relatively minor: fluid flow is never supersonic
> except in the vicinity of aircraft or objects like bullets which are
> travelling through a fluid faster than the speed of sound in that fluid.

	I've just been reading Rogers and Mayhew (Engineering Thermodynamics
Work and Heat Transfer) about venturi devices.  The reason I have been 
reading it had nothing to do the list, but the stuff I found is relevant.  Gas
flow can indeed be supersonic in convergent-divergent nozzles.  It's
described beginning at the bottom of p 380 in the ancient edition (1967)
I borrowed.  I can't say I worry about it overmuch, but it is interesting
stuff (and vital in some instances).

> The second point refers to the so called "empty tank dumping" syndrome.

	This _is_ a consequence of regulator design, and was described
here weeks ago.

> Here's my proposed theory:

	The point is that dumping was occuring when there was no needle
valve, so it isn't a consequence of valve characteristics.

> Pressure regulators control pressure. Needle valves
> control flow rates at a constant pressure. Both devices are required to
> - -accurately- control flow rates.

	Agreed.

	
-- 
Paul Sears        Ottawa, Canada