Pressure - where is it going?

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R.Chisholm

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Hi,

I own a 2 x 12l steel twin-set with Halcyon valves which I use in a DIR configuration including two Atomic M1 regulators.

Typically I assemble the full twin-set the day before I go diving and briefly put the regulators under pressure by opening both valves of the manifold to check for damaged o-rings and the like.

Providing there are no problems I typically close the valves again but leave the two regulators under pressure.

The twin-set when full typically has 200 bar of gas (air or nitrox) in it as shown by the SPG on the left post.

The SPG is the only device attached to a high pressure port on the left post - the other connections are a backup M1 secondary and an unattached dry-suit inflator hose.

So here is the question:

Typically when I return to the twin-set the next day the pressure on the SPG (with closed valves, but no pressure relief) shows 100-150 bar rather than the original 200.

Is this normal - is the pressure somehow slowly diffusing out of the second stage?

Just curious - according to various dive buddies there are no bubbles during a 3m bubble check - so no obvious leak.

regards,

Rory
 

lermontov

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you have a leak just go throw a process of elimination, have you tried a different set of regs to see if its the spg or a port cap, spg swivel etc
 

Ouvea

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A buddy of mine had the same issue. He would fill his tanks only to find them below full capacity a week afterwards. We finally traced it to the isolator. Gas was leaking through the isolator knob so it was making its way pass the seat. You might have the same issue where gas is leaking through the seat of the isolator or the posts valves. You could have a single sour or multiple sources. Servicing your manifold should resolve this issue.
 

D_Fresh

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A buddy of mine had the same issue. He would fill his tanks only to find them below full capacity a week afterwards. We finally traced it to the isolator. Gas was leaking through the isolator knob so it was making its way pass the seat. You might have the same issue where gas is leaking through the seat of the isolator or the posts valves. You could have a single sour or multiple sources. Servicing your manifold should resolve this issue.

In this case, he says the pressure shown on the SPG has reduced with the valves closed. So, as it sounds, is a loss of pressure in the regulator set, not the cylinders.

I agree with the above post, that considering the volume of air contained in the reg-set with the manifold valve closed, is so small that the loss of pressure overnight is likely nothing to worry about. But, if you want to chase down the issue, I would start at the SPG spool (why not change the spool o-rings anyways?), then move towards the 2nd stages. It may not be gas escaping to see bubbles right away, but if you put them in some water and stare at them for 10 minutes, maybe you might see a bubble come up.
 

Julius SCHMIDT

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Before you turn off the valves purge both seconds a few times to give the seats a chance to seat
 

Subcooled

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I typically close the valves [...] the next day the pressure on the SPG [...] shows 100-150 bar rather than the original 200.

A well maintained cylinder can retain its gas.
A cooling cylinder looses pressure of course (P/T=constant) ... maybe 10% but not 50%..

Edit: D_Fresh made a good point. I would not worry about air leaking from the regs as long as the cylinder contents are still intact.
 

Subcooled

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That is a pretty minuscule amount of air loss and not something that I would care about if no leakage could be discerned with a bubble check.

True indeed, if this pressure drop to 50% only happens in the regs and hoses, not in the cylinders.
 

halocline

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Hi,

I own a 2 x 12l steel twin-set with Halcyon valves which I use in a DIR configuration including two Atomic M1 regulators.

Typically I assemble the full twin-set the day before I go diving and briefly put the regulators under pressure by opening both valves of the manifold to check for damaged o-rings and the like.

Providing there are no problems I typically close the valves again but leave the two regulators under pressure.

The twin-set when full typically has 200 bar of gas (air or nitrox) in it as shown by the SPG on the left post.

The SPG is the only device attached to a high pressure port on the left post - the other connections are a backup M1 secondary and an unattached dry-suit inflator hose.

So here is the question:

Typically when I return to the twin-set the next day the pressure on the SPG (with closed valves, but no pressure relief) shows 100-150 bar rather than the original 200.

Is this normal - is the pressure somehow slowly diffusing out of the second stage?

I wouldn't worry too much about it, but if you want to investigate further, try adding another SPG to the right post reg and put IP gauges on the LP inflator and drysuit inflator hoses. Then leave everything pressurized with the valves shut again. You might get more information. Lets say that the right reg stays at 200 bar but the left one goes down to 100 bar and the IP has not budged. Then I might try simply switching the regs, do the whole thing over. If the pressure drop stays on the left post, you have a very slow valve leak downstream of the valve seat, maybe in a stem o-ring or some irregularity in the sealing surface where the regulator o-ring seats. If the pressure drop moves to the right post (same regulator) then you know there is a very slow leak in that regulator. That could be the DIN o-ring, maybe something in the HP ports. If you notice the IP dropping as well (this might be tough to see because it could drop a little, opening the 1st stage a smidgeon, which would then bleed air into the IP chamber, dropping the SPG but restoring IP) then you have a very slow leak in the 2nd stage or hose.

As people have mentioned, we're talking about a very small amount of air, nothing to worry about. But.....if you are still trying to hunt it down, the best way is to fill up a tub, set up everything, submerge in the tub, and settle in for a nice boring time watching and waiting for a bubble to appear. Maybe there's a good radio show or podcast you could listen to to help pass the time. If there's a leak, there will be a bubble sooner or later. Hopefully your significant other won't need to take a bath in the meantime!
 

beldridg

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It is a small amount of gas, especially overnight.

Assuming you have two LP hoses (Wing / Drysuit), I would check the Schrader valves on both of those. Also, if the wing inflator is connected, disconnect it to rule that out.

- brett
 
https://www.shearwater.com/products/teric/

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