More qualitative testing results on Porter VCD1000 MCCR valve

teksimple

FYI, split from Expedition-level Mk 15.x MCCR in 90 seconds!

Just got back from the Channel Islands where I did all the dives using my Porter Instruments VCD1000 ("Msense") adapted to my Mk 15.5. I did not plan to dive the Msense on this trip originally, as I just received a new electronics pod from Kevin Juergensen. Unfortunately the sensor 1 lead on the primary side of the six pin connector on my JM horsehoe board crapped the bed. I would never begin a dive using electronic control based on two sensors, but am reasonably comfortable using two sensors and manually flying the rig, so I did just that for all three days of diving (no scolding, please) Yes, a little risky, but since the technical dive leader vetoed the use all the helium we just bought (unacceptable labeling!) all our dives were limited to rec depths.

After this and my new dose of skepticism, I am absolutely convinced now that a relatively constant mass flow is a reality with the VCD1000. At least in a moderate depth range.

The deciding moment was the 30 minutes I spent filming an anemone at 47 meters. No excess oxygen, had to tap my manual add valve once to keep it at 1.2, about the same rate I was on deco in shallow water.

If we were dealing with just an orifice or laminar flow element, would expect the flow rate to nearly quadruple with increasing ambient pressure. But the VDC1000 has both a regulator AND a laminar flow element. These keep the mass flow relatively constant in all the testing and depths that I have dived it.

Quantitative results are still lacking. Qualitatively, this thing has exceeded all of my expectations.

Calling anyone with a chamber or LARGE pressure pot...

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Dave Sutton

Good deal!

Who would have guessed?

DrMike: You play with yours yet? (wait... that's not what I meant to say......)

Looks like mine needs to come out of the box under the bench and get into a rig.


Dave

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jaap

Nice thing to hear

I'm simply curious about the helium thing. Is it too much to ask about further details? We always use the He-cylinders (after some beyond average customer probing) with questionable labeling for many 100s of dives since many years ;-)

Would the flow really be expected to quadruple in the above case to 47m? My crude testing of non fixated (non plugged) IP regulators on a small CMF flow does not indicate anyway near that sever increases in flow?

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teksimple

The individual who charted the boat was a DIR instructor who had several students in tow, so assume that he was setting an example more than anything else. He said that I could use it if I liked, but that would still leave me diving extended range solo, with only two sensors.

You are exactly right. I should change my first post. Density and viscosity increases which reduces flow and therefore flow would NOT increase at a rate proportional to pressure. Very basic fluid dynamics. However, flow SHOULD increase significantly when pressure is quadrupled with either a laminar flow element or simple orifice.

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SimonK

Some more thoughts on how this thing works.

We have a laminar flow device with a built in regulator that controls the pressure drop across it to give constant volume flow.
The input pressure is ambient plus the O2 reg IP. Assume the IP is 10 bar and the drop across the device is adjusted to 1 bar to give the desired surface flow rate. At the surface the input pressure will be ambient (1 bar) + IP (10 bar) = 11 bar. At 40m the input pressure will be ambient(5 bar) + IP(10 bar) = 15 bar. So the mass flow of oxygen will be 15/11 = 1.36 times the surface mass flow.

Dodgy physics aside the thing obviously works well enough to meet the main requirment of saving a dive trip when the electronics pack up.

Simon

Dave Sutton

A *perfect* example of DIR: Being an inflexable ass in front of everyone. I hope the students got a *good* lesson.....

What in the *world* could be wrong with your helium?


I never cease to be amazed at the way small minds work.


Dave

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jaap

OK

My limited testing (9.5 bar on the surface) gives something close to the findings of the Pelagian-folks. I believe their finding is an about 1% increase per meter depth.

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Rebreatherlab

Keep the IP at 9 and you will have exactly 1% per meter down to about 90 msw. Deeper the flow goes sub sonic and the increase is no longer linear, but using the full equations with temperature drop, friction etc. you get a difference from the "1%/m" that is neglectible even at 300 msw. The reason being that you will likely not carry a laboratory grade flow meter that could pick up the difference when you set the flow on the boat. With a needle it is of course easy to adjust if needed.

Andy

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