PMV adjustment help

[Scuba_Si]

Hi,

I got a new PMV and im having trouble calibrating it. I can get it to pop open at 180 bar no problem, But once it opens it sticks and does not close again until i drain quickly down to 0 bar. THe PMV kicks in at about 120 if i do a rapid decompression via the fill whips.

So to summarise:

'Empty' Tanks at 50 bar, pressure rising in fliter stack, all good.
Filter stack hits 180 Bar, PMV pings open with a big click.
Pressure equalises out to say 70bar throughout the entire system ,all the way to the filters.

If i depressurize quickly using the fill whips i can keep about 120 bar in the filter stacks, but with a slow depressurisation with 4 tanks attached i see no benefit from the PMV.

Why is the valve reacting so differently in depressurisation / repressurisation cycles?

Any help greatly appreciated.

 

[divingtactics]

We need some additional information from you on your PMV. Make, model etc. If it is an AE version, I've had trouble with two of them. The Lawrence Factor heavy duty one is much better in build quality and performance.

It should open at 150 bar and then close at around 100 bar. Rapid depressurization shouldn't make a difference. Once it is open, it should remain open, so if it opens at 150 bar, it should remain open till you finish your fill at 230 bar. When you bleed down you whips, it should close at 100 bar and keep that pressure in your tower. I fitted a pressure gauge to my tower before the PMV, so I can confirm constant pressure being maintained after the system is shut down. 180 bar is a little high for little benefit, you are better to set it at 150 bar opening pressure as this is a better balance point for most compressors.

So a PMV will build up pressure in your stack from 100 bar to 150 bar, then open and cause a quick pressurization in your whips from 0 bar to 150 bar and allow gas to pass through, then it will remain open and pressure will rise in your system at normal levels according to your compressor condition and rated free air delivery value. When you turn off your compressor and bleed your whips down, the PMV should close and keep pressure in your stacks but the whips will bleed down to zero.

The benefit of a PMV is to keep the compressor in a better state of balance up to 150 bar and to increase your filtration dwell time. The reason to keep pressure in the system when it is not being used is to keep all the nasties held in suspension within the filtration media and to keep ambient moisture out of your molecular sieve.