Both Octos Leaking Bubbles from Mouthpiece, just serviced

[TinFins]

Hi All,
I got my wife and my regs serviced last week. First dive we are at altitude (Lake Tahoe) and both octos were "blowing" small bubbles at the surface even with the mouthpiece pointing down, before and after the dives including out of the water. Is this something to do with altitude, and reduced pressure on the valves? Or do I need to get the regs re-serviced? If it matters, both octos are scubapros.

Thank you

 

[knotical]

Assuming your regs were serviced in San Francisco, it sounds as if you have already diagnosed the issue. The lower ambient pressure at altitude might indeed permit a mild free-flow. I'd say your tech did a good job of tuning.

 

[halocline]

The lower ambient pressure at altitude might indeed permit a mild free-flow.

Considering the fact that both the 1st and 2nd stages of all scuba regulators automatically adjust to ambient pressure, I'd say this is highly unlikely. It sounds to me like IP was set a little too high or both 2nd stages set a little too lightly. But, it's possible there's something I'm not thinking about. The thing is, IP is always "X" above ambient pressure, if the ambient pressure at altitude is substantially lower (not much compared to changes in ambient under water) then the IP should automatically lower by the same proportion.

To the op, when you say "both octos" I assume you mean your alternate 2nd stage and your wife's alternate 2nd stage were leaking, but that neither of your primary 2nd stages were leaking. Is that correct? And if your alternates are unbalanced, and your primaries balanced, then the alternates would be more susceptible to higher-than-normal IP.

As an experiment, get a tank and try it again at sea level, I'd be curious to know what happens.

 

[LeadTurn_SD]

Interesting question regarding elevation change, and I'm embarrassed to say I'm not positive about the answer.

My feeling is that it is a 2nd stage tuning issue rather than elevation.

From San Francisco to Lake Tahoe the drop in air pressure acting on the first stage (the ambient pressure) is less than 5 psi, and, would not a drop in ambient lower the IP??

With sealed diaphragm first stages this is really easy to demonstrate... hook up an IP gauge, and with the first stage pressurized press on the external diaphragm (environmental seal) to simulate increasing ambient pressure, and watch the IP rise on the gauge. Thus, decreasing ambient would lower the IP.

I'm not really sure, but there are other folks who certainly know; hopefully they will chime in.

Best wishes.

 

[halocline]

From San Francisco to Lake Tahoe the drop in air pressure acting on the first stage (the ambient pressure) is less than 5 psi, and, would not a drop in ambient lower the IP??

Yes it would. The IP is the force required to close the valve working against the spring and ambient pressure, so a drop in ambient would lower the absolute IP. Even though there's no water pressure pushing against the piston, there is air pressure. It's easy to forget that.

The 2nd stage should experience a net zero change in forces, as the pressure inside and outside of the diaphragm will always equalize.

 

[TinFins]

I will test back at sea level tonight and let you know what happens. And yes, by both octos I meant mine and my wife's, primary seconds were both fine, but maybe that's because we put them on low flow mode before getting in the water.

 

[TinFins]

And the winner is....... Knotical!

I brought the regs down to sea level and the leaks stopped immediately. It must be the pressure differential at 7,000 feet to the intermediate pressure is not sufficient to keep the valves completely closed.

Thanks all for your help, this is good information for people planning to dive at altitude. Especially Lake Titicaca.

 

[redacted]

And the winner is....... Knotical!

I brought the regs down to sea level and the leaks stopped immediately. It must be the pressure differential at 7,000 feet to the intermediate pressure is not sufficient to keep the valves completely closed.

Thanks all for your help, this is good information for people planning to dive at altitude. Especially Lake Titicaca.

It seems to me that your octos are tuned a bit too hot.

 

[halocline]

I brought the regs down to sea level and the leaks stopped immediately. It must be the pressure differential at 7,000 feet to the intermediate pressure is not sufficient to keep the valves completely closed.

I'm sorry to tell you this, but again, IP is always a specific amount above ambient pressure. That's the way all regulators function; if not, they would not work for diving at various depths. The pressure differential between ambient and IP is the same regardless if you're at sea level, on the top of Mt Everest, or at 200ft of depth.

Plus, what you're saying with "the pressure differential not being sufficient to keep the valves closed" makes no sense, here's why. For the 2nd stage valves, IP is trying to open the valves, not close them. Less pressure differential between ambient and IP (or, for all intents and purposes, lower IP) would result in less force opening the 2nd stages, i.e higher cracking pressure, not lower. It would make a slight free flow less likely, not more.

For the first stage valve, IP is by definition the pressure required to close the valve. If there's a leak at that valve, it means IP is creeping up. If your free flow was caused by IP creep, which is a possibility given that the balanced 2nds did not leak, then you need to start by measuring the IP and making sure it locks up quickly and within the given spec, which for SP 1st stages is between 125 and 150 PSI. I like to set my balance piston SP 1st stages on the low side, around 130.

What I had been wondering about was if there was something that would prevent the first stage from automatically compensating, i.e lowering, the IP at altitude. That would result in a higher-than-normal IP, or a larger pressure differential from ambient. That could cause a leak. But I can't think of anything that would cause that. Maybe some sort of problem with something like the sherwood dry bleed system, but that's a stretch.

So I suspect your leaks had nothing to do with altitude; much more likely they were related to the recent service. Slight freeflows, especially in unbalanced 2nds are not uncommon after service.

 

[TinFins]

I'm sorry to tell you this, but again, IP is always a specific amount above ambient pressure. That's the way all regulators function; if not, they would not work for diving at various depths. The pressure differential between ambient and IP is the same regardless if you're at sea level, on the top of Mt Everest, or at 200ft of depth.

Plus, what you're saying with "the pressure differential not being sufficient to keep the valves closed" makes no sense, here's why. For the 2nd stage valves, IP is trying to open the valves, not close them. Less pressure differential between ambient and IP (or, for all intents and purposes, lower IP) would result in less force opening the 2nd stages, i.e higher cracking pressure, not lower. It would make a slight free flow less likely, not more.

For the first stage valve, IP is by definition the pressure required to close the valve. If there's a leak at that valve, it means IP is creeping up. If your free flow was caused by IP creep, which is a possibility given that the balanced 2nds did not leak, then you need to start by measuring the IP and making sure it locks up quickly and within the given spec, which for SP 1st stages is between 125 and 150 PSI. I like to set my balance piston SP 1st stages on the low side, around 130.

What I had been wondering about was if there was something that would prevent the first stage from automatically compensating, i.e lowering, the IP at altitude. That would result in a higher-than-normal IP, or a larger pressure differential from ambient. That could cause a leak. But I can't think of anything that would cause that. Maybe some sort of problem with something like the sherwood dry bleed system, but that's a stretch.

So I suspect your leaks had nothing to do with altitude; much more likely they were related to the recent service. Slight freeflows, especially in unbalanced 2nds are not uncommon after service.

I admit that my language was probably wrong, I am not a reg technician and am still learning how regs work. I would say that at elevation both octos had a slight hiss the second I hooked them up to the tank by the truck. This hiss continued once at the surface and ceased once ~two feet deep. I'm not saying you are wrong, I'm just saying that empirically, the only variable that changed was the altitude. When hooking up the regs at sea level, the hiss is gone.

Respectfully,
Tim