Drain valve on cell test, shall I exchange it?

[Agro]

CCR Liberty oxygen sensor test kit is designed for automated validation of cells while mounted in the head. This cell tester turns the Libery head into a 3.5 bar pressure chamber. It flushes the head several times with O2, I must manually open the drain valve. Problems:
1) The drain valve is rather poor qualitiy, it looses very small chrome plates, you don't want this in a rebreather.
2) The drain valve is hard to close, it's leaking. I must use a pliers, producing even more chrome plates.
3) The flow is rather small, I have to wait some moments until pressure goes down from 3.5 bar to 1 bar. You have to open the valve several times, that's annoying.

I guess the slow decrease is not necessary for cell test. So I ask myself if I could add another drain valve for ex. the one in the picture (here on a filling hose), it has much more flow and better qualtiy.

What do you thing about this idea?

 

[tbone1004]

Your point 3 is actually very important, you do not want the cells to be cycling rapidly with pressure, it will cause a lot of damage if you expedite the process. If the screw is leaking then you need to call Divesoft and see if they will replace it because you shouldn't need to wrench on it but you do absolutely do not want to increase the speed of pressure change.

 

[Agro]

Sounds interessting but I do not understand how fast pressure change my dammage the cell. My idea:
- pressure increase must be rather slow to give cells the time to react on pO2 change.
- pressure decrease is necessary to flush the unit compeltely with O2, air must be washed out, therefor some cycels are done. During decrease there is no cell reading going into protocol, so decrease might be fast.

Or do you think of a physical dammage on the cell? Is there any chance to do so? I thought they always have the same pressure inside and outside, isn't this the case?

 

[tbone1004]

physical damage to the cell can occur with rapid pressure changes. The electrolyte is still captured and they like to leak if you decrease pressure too rapidly. You also need time for the cells to "calm down" on the pressure drop you are not just looking for linearity and current limiting, you are also looking for response rates in both directions.

 

[Agro]

physical damage to the cell can occur with rapid pressure changes. The electrolyte is still captured and they like to leak if you decrease pressure too rapidly. You also need time for the cells to "calm down" on the pressure drop you are not just looking for linearity and current limiting, you are also looking for response rates in both directions.

Sounds reasonable. I will open a cell and have a closer look to it. And I just bought
As I am not happy with Divesoft's drain valve I will exchange it against a better one: no chrome coming off, no metal-to-metal sealing but plastic-to-metal sealing -> possbility to service it. This new valve has much more flow which is no good, as I have learned from tbone, so I will add a nozzle, reducing the flow to original.

 

[Gone for diving]

Some bleed valves leak though the threads. That makes it slow.. . Sounds like that's what you want....

Others have a cross drilled hole close to the seat which vents fast...

 

[Agro]

The Divesoft valve leaks through the thread, yes that makes it slow.

My new valve in fact has the cross drilled hole, therefor vents faster. I will use this valve but add a nozzle.

 

[Agro]

I got an answer from a Vandagraph engeneer: a cell sometimes has very small gas bubbles in there. Fast pressure change may dammage the cell membrane the same way it does in our body. I call this sensor's DCS So I am waiting for my nozzle which I will definitely add to my pressure relieve valve.