Flowstop on bottom gas bailout?

[tomsch]

I started with rebreather diving(tdi helitrox) last summer and am currently starting with simulated and real deco dives with enough deco time to make a 50% O2 stage viable. But apart from that I thought a little bit about BO configs and the idea on a flowstop, like the one apeks produces, on my bottom gas BO tank sounds good in my opinion for the following reasons:
- I like my BO tanks to be closed. With a flowstop I can have my tank open without the possibility of loosing air and without having to open the tank, which takes more time then just opening the flow stop.
- If my 2nd stage would have a freeflow, I'm often diving in 4C water, especially in winter, I can still breath from it.
- Swapping 2nd stages underwater in case of problems has a much higher success rate

A disadvantage would be that it's an additional point of failure (requires over pressure valve and flow stop, so +2x).

I know this will get some reactions on how stupid this idea is but I'm still curious about your answers.

 

[tbone1004]

I would recommend against them. They are also big and bulky which can make them uncomfortable if you have to bailout. You don't describe which unit you're diving on but I feel really strong about having either a necklaced bailout regulator or a BOV which needs to be always on and readily accessible. If you have one of those, then you should not have to get onto any of your tanks like a 50% bottle so fast that you can't turn a tank valve back on. I do not understand why instructors teach diving with bailout closed, I really do not, granted some also teach to have a BOV attached to the onboard 2l or 3l which is even more ridiculous but that's a different discussion.

1-the tank valve takes a negligible amount of time longer vs. a flow stop so I would not use that argument. The flowstops have their place for certain applications but bailout second stages are not one of them.
2- why would a flow stop allow you to breathe from a tank when feathering the valve wouldn't? The advantage of feathering the valve is it is less of a hammer when you do open it back up.
3-don't have that as part of your SOP, not worth thinking about.
4-the flow stops themselves are usually fine, but the OPV's are notoriously leaky and I try to avoid them at all costs. I use Poseidon first stages on regulators that require them since they have seemed to build one that doesn't leak and it's built into the body but I haven't found a port plug one that I like.

 

[grantctobin]

I think a flow stop on a primary bailout or a BOV is a fool’s errand.

Appears TBone beat me to it. Would you add a flow stop to your necklaced reg in a set of doubles? If not, don’t add one to your bailouts or BOV. BOV or always on, breathable, necklaced bailout.

 

[rjack321]

I started with rebreather diving(tdi helitrox) last summer and am currently starting with simulated and real deco dives with enough deco time to make a 50% O2 stage viable. But apart from that I thought a little bit about BO configs and the idea on a flowstop, like the one apeks produces, on my bottom gas BO tank sounds good in my opinion for the following reasons:
- I like my BO tanks to be closed. With a flowstop I can have my tank open without the possibility of loosing air and without having to open the tank, which takes more time then just opening the flow stop.
- If my 2nd stage would have a freeflow, I'm often diving in 4C water, especially in winter, I can still breath from it.
- Swapping 2nd stages underwater in case of problems has a much higher success rate

A disadvantage would be that it's an additional point of failure (requires over pressure valve and flow stop, so +2x).

I know this will get some reactions on how stupid this idea is but I'm still curious about your answers.

Were you trained to swim around with your primary (deepest) bailout shut off?

 

[Garth]

Definitely not a good idea. I’ve seen people use them on tanks they plan to leave staged in part of the cave and felt they would have less chance of loss of gas.
Neither are necessary and the act of opening the valve is part of the process to ensure you have the right bottle.

I would advise against putting a flow stop.

Some use them on their rebreathers to stop the flow of oxygen instead of closing the valve. This practice is also frowned upon because people have died with the flow stop closed.

Tank valves are the best flow stop.

 

[Jack Hammer]

Tank valves are the best flow stop.

+1
Tank valves have all the upsides without any of the downsides.

 

[macado]

I don't have too much more to add but I feel like inline shutoffs / flow stops are solution looking for a problem. I do know people that use them but I honestly do not recommend them. I'm not going to go ahead and disavow their usage and say they're stupid but just that I've seen them cause more problems than they fix. I will concede that they can probably can be useful in specific fringe use cases.

In a real bonafide emergency it's one more thing keeping you from getting breathable gas RIGHT NOW. In fact, I watched someone bailout not remembering they had in-line shut offs on their bailout regulator and almost have a very bad day and drown. They immediately took them off their second stages after that incident.

I see people that use them generally for these reasons..
1) They are "cheap" and dont want to loose their precious trimix from purging regulators or bubbling second stages. Honestly just fill your bailouts to 3200-3300psi (~225bar) and fix your second stage LP seats.
2) Leaving stage bottles somewhere and leaving them on. Why not just turn them off?
3) They are scootering and are afraid of losing gas. In general, slight detuning and regulator positioning helps with this problem. For stage/deco bottles I just habitually crack valves on/off to make sure they're pressurized but I recognize I've probably also flooded more first stages than I care to admit.

If you do use in-line shuts offs (I'm sure this has already been said). Please put an OPV on your first stage otherwise if and when the HP seat fails you're going to need new underwear if you're on land, in addition to some new LP hoses.