cloudflint
Contributor
In my case i just turned the tank valve on a bit every time i wanted to breathe in. It worked surprisingly well.
Why no regulator shutoff?
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If your second stage turned off when your first stage freeflowed, the excess pressure would likely rupture the hose. This puts you in a similar, but much worse, situation.
DevonDiver
N/A
As Adelman and Dave state, most freeflows will actually originate from the 1st stage. If so, having a shut-off to isolate the primary first stage will only continue the problem - as the AAS will then begin to freeflow.
I had a reg-freeze freeflow whilst diving at 36m in an ice-cold quarry. It emptied a 15l cylinder in under 3 minutes. This was the time it took me to get orientated, reassure my buddy and begin an ascent. The cylinder had completley drained when I got to 15m. The rate of gas loss was incredible. I tried to breath the free-flow, but it coated my front teeth with ice (ouch!) I finished the ascent using a pony cylinder. No dramas (apart from sensitive teeth afterwards).
Whilst you can buy in-line 2nd stage shut-offs, you rarely see them used. That illustrates their worth.
For recreational diving, a freeflow is far from a catastropic failure. You could still breath from the freeflow. You should have a buddy available for air-sharing. You won't be far from the surface, so a controlled ascent using either solution is entirely achieveable.
If freeflow is a particular, personal, concern for you - then you need to address 1st stage shut-down. This will mean one of 3 common solutions:
1) Double tanks, with isolating manifold. Selective shut-down of valves preserves access to all of your gas in the event of 1st stage failure. If the tank valve itself should fail (rare) then the isolator will preserve 50% of your remaining gas. Gas management/planning ensure that you would always have sufficient air to surface.
2) Single tank with H valve. Whilst not as functional as doubles, this solution provides you with the option to shut down a free-flowing 1st stage and still access gas via another 1st stage. It is not true redundancy of gas. Neither does it provide a solution for tank valve failure.
3) Redundant cylinder (i.e. pony). You could transfer to a redundant cylinder (pony/bail-out) and shut down your primary cylinder. The only benefit to shutting down the primary cylinder would be to reduce distraction from the bubbles - but you may get lucky and be able to access the gas again at a later stage. If the free-flow is caused by icing - shutting off the cylinder may allow a thaw and the regulator to be re-used at a shallower depth. However, a prudent diver will have planned their gas requirements to ensure that their redundant cylinder has sufficient gas to get them back to the surface.
If you are doing deeper diving, or actual/virtual overhead environments, then you will need appropriate redundancy. In most cases this will consist of double cylinders with an isolating manifold.
I had a reg-freeze freeflow whilst diving at 36m in an ice-cold quarry. It emptied a 15l cylinder in under 3 minutes. This was the time it took me to get orientated, reassure my buddy and begin an ascent. The cylinder had completley drained when I got to 15m. The rate of gas loss was incredible. I tried to breath the free-flow, but it coated my front teeth with ice (ouch!) I finished the ascent using a pony cylinder. No dramas (apart from sensitive teeth afterwards).
Whilst you can buy in-line 2nd stage shut-offs, you rarely see them used. That illustrates their worth.
For recreational diving, a freeflow is far from a catastropic failure. You could still breath from the freeflow. You should have a buddy available for air-sharing. You won't be far from the surface, so a controlled ascent using either solution is entirely achieveable.
If freeflow is a particular, personal, concern for you - then you need to address 1st stage shut-down. This will mean one of 3 common solutions:
1) Double tanks, with isolating manifold. Selective shut-down of valves preserves access to all of your gas in the event of 1st stage failure. If the tank valve itself should fail (rare) then the isolator will preserve 50% of your remaining gas. Gas management/planning ensure that you would always have sufficient air to surface.
2) Single tank with H valve. Whilst not as functional as doubles, this solution provides you with the option to shut down a free-flowing 1st stage and still access gas via another 1st stage. It is not true redundancy of gas. Neither does it provide a solution for tank valve failure.
3) Redundant cylinder (i.e. pony). You could transfer to a redundant cylinder (pony/bail-out) and shut down your primary cylinder. The only benefit to shutting down the primary cylinder would be to reduce distraction from the bubbles - but you may get lucky and be able to access the gas again at a later stage. If the free-flow is caused by icing - shutting off the cylinder may allow a thaw and the regulator to be re-used at a shallower depth. However, a prudent diver will have planned their gas requirements to ensure that their redundant cylinder has sufficient gas to get them back to the surface.
If you are doing deeper diving, or actual/virtual overhead environments, then you will need appropriate redundancy. In most cases this will consist of double cylinders with an isolating manifold.
Thanks for the info. I had not thought about the first stage sticking, and having to be relieved through the second stage. I certainly wouldn't want a hose rupturing at 400+ PSI next to my face. My buddy and I both figured there must be a very good reason not having a shutoff but, other than "You could accidentally have it off and cause a panic in a diver who didn't know about it", we couldn't think of what it was.
Scott and MSA belt mount regulators for the fire service were fed by a high pressure hose and had a shut off valve with a locking button to prevent accidental closure and a bypass valve to supply gas in case of a free flow. A similar shut off could be plumbed for scuba, but high pressure hoses up to the shut off would be a requirement. Low pressure hose could be used between the shut off valve and the secondary.
DevonDiver
N/A
You could forgo the high-pressure hose and just fit an Over Pressure Valve (OPV) into the regulator 1st stage.
https://www.techdivinglimited.com/overpressure-valve-p-500.html
That'd ensure an outlet for gas. I used these with argon bottles for drysuit diving before. The chances are that a 1st stage free flow would just divert to the AAS if the primary was shut down.
It's still a never-ending circle though.... the end result is that it won't provide you with a functioning regulator and air supply... and gas will still be escaping.
From a diver's perspective, the solution to a 1st stage free-flow is a trustworthy buddy or an adequate redundant air source.
You know, I feel about a second stage shutoff about the way that I feel about the first stage gadgets that automatically close the inlet to the first stage, so you can't get water in them when you soak them. I, personally, do not want ANYTHING in the entire sequence from the tank to my mouth that can close off my gas, except a valve that requires my manipulation to do it. Anything that can go wrong, will; Murphy was completely right. If my reg fails, I want it to fail by delivering too MUCH gas - I can breathe off a free-flow for a short time, until I can establish gas-sharing with a buddy, or shut a post. If I just suddenly and without warning have no gas, it's a much bigger emergency.
Please understand, I'm only playing devil's advocate and suggesting what could be done based on president in other areas of scba. The one advantage of it over an overpressure valve is that you would not lose massive amounts of gas. Consumption would not be much greater than if everything were working correctly. With that said, I can't see myself ever going to the trouble.
Knowone, I can't tell if your trying to be funny or sarcastic or both, but in my opinion, the introduction of integrated electronics into what used to be a very robust piece of fire fighting gear is a travesty.
Knowone, I can't tell if your trying to be funny or sarcastic or both, but in my opinion, the introduction of integrated electronics into what used to be a very robust piece of fire fighting gear is a travesty.
CuNanoTube
Contributor
In the event of a first stage free-flow you could reach back and turn off the valve of your doubles... if you were a tech or tech hopeful diver. Realistically the average diver would just switch to their pony / buddy's tank and turn their main off. I personally have only heard of one instance (father's dive buddy) where a first stage froze, but then again, all the people I dive with use cold water gear. My second has frozen before on me, but since I dive with an environmentally sealed first there would have to be a serious problem for it to freeze.
Also, the cooling of gas when it expands (it takes energy to expand) is called the Joule-Thomson effect. It is the same effect that allows artificial snow to be made at above freezing temperatures.
Also, the cooling of gas when it expands (it takes energy to expand) is called the Joule-Thomson effect. It is the same effect that allows artificial snow to be made at above freezing temperatures.
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