[APD] Re: Ooch

["Tom Wood" <tomwood2 at flash_net>]

"Is it that the pressure differential with the CO2 set-ups is not great 
enough for a sonic velocity to be acheived at the metering valve (critical 
pressure ratio?) or that the metering valve opening in these setups is too 
large for critical flow?"

Both and neither because we aren't using the valves in a way that any of 
that applies.

Here's a simple experiment, especially for the Fabco NV-55. Set the 
regulator to about 25 psi and the valve to a couple of bubbles or so per 
second. A typical setup. Now apply some suction to the line out of the 
bubble counter (don't inhale). If the bubble count increases, then by 
definition it wasn't sonic to begin with. Yet all these needle valves do a 
perfectly fine job of preventing a dump. Why?

TW 


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