Check valve for p-valve

[skdvr]

I am looking to make my own p-valve for another DS that I have. I want to make it balanced so I need a check valve. I have Vance Harlows book on DS repair and was going to follow the instructions that he has, but the check valve that he reccomends (well the pt number he gave and place to buy from) but they have minimum order standards that are way beyone the number of p-valves I will be making. So have any of you made your own balanced p-valve, and if so what check valve did you use. I found some at usplastic http://www.usplastic.com/catalog/category.asp?catalog%5Fname=USPlastic&category%5Fname=45&Page=1 I just am not sure which would be best, if they would work at all...

Anyway, just looking for your experience if you have any with DIY p-valve

Thanks
Phil

[scububa]

FWIW

I don't have any experience, but from your reference page, there seem to only be 2 that are relevant. The Check Valve and the Mini Check Valve.

Of those 2, the Check Valve appears to be the choice. Depending on your operational depth, numbers would vary. But, the Check Valve is spec'd for a value in the 300' depth range (but with no real design margin). The Mini gets you around 200' (with no margin.) So, the Check Valve gives you a decent desing margin at 200'. Also, the cracking pressure is less for the Check Valve. An operating pressure of 225 psi would give you a 50% margin at 300'.

[b1gcountry]

http://www.mcmaster.com/

search on abs check valve. If you order from them, also check out the quick disconnects they sell. There's a link on TDS somewhere.

Tom

[do it easy]

Hold on a second... Those US Plastic check valves have a 1 psi cracking pressure, which doesn't sound like a lot, but I think "red" check valves have a cracking pressure in the .1 psi range.

I think either it wouldn't work or, worst case, you might end up with a hickey where the sun don't shine.

There are some check valves from McMaster that have a .5 psi rating. This might still be a bit high. I think as a rule of thumb, you should be able to blow through the valve to overcome the cracking pressure. The pressure difference in your drysuit isn't as high as the ambient pressure around you.

[DeepDiverBob]

you should be able to blow through the valve to overcome the cracking pressure.

I highly recommend this test before using it on your suit. (Ken)

[scububa]

Hold on a second... Those US Plastic check valves have a 1 psi cracking pressure, which doesn't sound like a lot, but I think "red" check valves have a cracking pressure in the .1 psi range.

I think either it wouldn't work or, worst case, you might end up with a hickey where the sun don't shine.

There are some check valves from McMaster that have a .5 psi rating. This might still be a bit high. I think as a rule of thumb, you should be able to blow through the valve to overcome the cracking pressure. The pressure difference in your drysuit isn't as high as the ambient pressure around you.

Actually, the Check valve has 0.5 psi cracking, which is why I pointed it out. (The mini has 1.0 psi) But, I am not sure of what parameter value is valid here. In general, it seems the lower the better, but if it gets too low, at some point it will effectively be always cracked (in other words, not really a valve).

[MgicTwnger]

I highly recommend this test before using it on your suit. (Ken)
That sounds like the voice of experience. Now that picture will be stuck in my head all day.

[skdvr]

Actually, the Check valve has 0.5 psi cracking, which is why I pointed it out. (The mini has 1.0 psi) But, I am not sure of what parameter value is valid here. In general, it seems the lower the better, but if it gets too low, at some point it will effectively be always cracked (in other words, not really a valve).

I think that being open pretty much all the time would be OK, it should close if you get preassure from the opposite direction (fluid). I saw on Salvo's site that they sell the check valves that they use in their p-valves so maybe I will just order two of them, since I know that those are used all the time. I really do not want a hickey

I checked with smart products (reccomended from the book) and they do have a 25 piece minimum order, so I will not be using them. It is understandable though because all the valves that they sell are custom made. Which would be nice but I do not need 25 check valves...

Thansk again everyone for your input...

Phil