Using Adjustable Needle Valves

Digger

OK, quick question, partly because I have a swaglok adjstable in the workshop, and wondered if it might be useful.

Now Duncan said this of Rick doing 160m on the KISS:
"the only modification was the substitution of a needle valve and bypass with depth compensated first stage for the usual KISS valve and fixed IP first stage."

Right then, my swagelok with a fixed IP is bang on my resting rate at 12.5 bar. I used to use an Apeks to do this, and it worked just like a KISS vlave, no adjustments necessary.

Now, what would be the difference between me running a fixed IP of 12.5 bar and using a compensated reg running at say 4 bar IP over ambient. Once I got to 75m surely the rate would be the same (12.5 bar hitting the orifice) and below 75m would be too high for me, and end up with rising ppO2 all the time?

Basically, if the orifice with the swaglok set all the way down is the same size as the KISS, how does it make it possible that you can go deeper than the limit of the valve?

Thanks in advance. I've probably missed something very obvious, it just doesn't quite line up in my head at the minute. Unless he did something completely different somewhere along the line.

Digs.

lizardland

I would have thought a metering valve dialled right down was a lot less than a KISS valve. On mine I needed about 1.25 turns to get a flow equal to metabolic. The flow on mine on the lowest setting was barely a trickle, though the valves aren't rated for shut-off use. Orifices aren't really linear, a reduction in size doesn't necessarily give a proportionate reduction in flow.

I've got an Excel spreadsheet somewhere that does a fairly accurate calc based on the valve's data sheet and the reg's IP. It even predicts the right number of turns to open the valve to get a certain flow rate.

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decoweenie

What if it is not ?

Do you know what is the minimum cross flow area of the Swagelok ?

dave t

my swagelok valve shuts off completly!!

decoweenie

Jeez thanks Dave, it was rhetorical...