What effect does the tank valve have on air consumption?

[milbournosphere]

My buddy forgot to fill one of his tanks, so he borrowed one of mine for the second of our weekly dives this week. The first dive (on his tank), his SAC rate was what it usually is. The second dive (on my tank), his SAC was was significantly improved. He got an additional 10 mins (a marked increase considering he usually bangs out 35mins on an ALU80) out of his 80cuft of gas than he normally does. His tanks have Sherwood valves on them, the tank he borrowed from me has a USD k-valve (It's a USD luxfer tank); both are Yoke valves.

I'm no expert, but the difference in dive times, at a site we have dove many times (and dive regularly) was kind of surprising. It got me to thinking (dangerous, I know)...what effect does the valve (or the condition of the valve) have on air consumption? I'm not saying it's the valve, but we were both a bit curious with the difference in dive time.

 

[Scared Silly]

None practically. What may have well happened (especially given the water temps) that he and his body relaxed thus needed less air. Remember the valve is delivering gas at a high pressure, where it is reduced then delivered by the first stage, as such it is highly doubtful the valve made any difference. That said he may want to check his valves for an obstruction and to make sure they fully open.

 

[milbournosphere]

We considered the 'well, you're just really relaxed' option, but we dive this site weekly and have two years of computer data backing up the sac rate and temperature fluctuations. This was a large increase relative to the historical data, albeit with a sample size of one. I wasn't thinking 'well, my valves are just awesome', but rather that his might need overhauling, resulting in more work being required to breath, perhaps, but I'm no expert. I'm going to use one of his tanks next dive and see if I see/feel a difference.

 

[mala]

maybe your tank is lighter?
so if he was overweight with his he would be less overweight with yours?

maybe you get better fills ?

maybe your tank trims better?

anyway I think that 35mins underwater is long enough with a yoke reg.

 

[Jim Lapenta]

What depths were you diving? Not that it really makes a difference or should but curious what dives limit you to 35 minutes on an al80.

 

[milbournosphere]

I think that 35mins underwater is long enough with a yoke reg.

Care to elaborate?

Jim, this would be a 70ft dive or so. His calculated SAC according to Subsurface is .65 or so to my .45-.50.



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[emoreira]

Perhaps the valve needs maintenance and is having flow restrictions, which makes breathing harder. With this, an increased SAC could be expected as the extra effort required to breathe. I remember using an old rented J valve tank which, even full opened, on each breathe the SPG showed a down pulse in the HP side, with increased breathing effort.

 

[Nemrod]

The valve has no effect upon air consumption.

N

 

[Rich Keller]

My best guess is that he was just more relaxed on the second dive. Another possibility is that the tide was going out and the second dive took place is shallower water.

 

[captain]

The valve has no effect upon air consumption.

N

This.