Swapping regs

[Sludge]

This is from another thread:

"... independent backmounted twins. If you lose one regulator, you can't get at the gas in that tank, like you could in sidemount..."

Has anyone ever actually done this? I mean, remove a reg from one sidemounted cylinder, hold your breath, remove the other reg, and install it on the first cylinder.

I'm not asking if you think you can do it. I'm asking if you ever did, either in an actual reg-failure situation or in a pool as an exercise.

(I realize the possibility exists where there is a reg "failure" such that the second stage freeflows and a sidemount diver can "feather" the valve open and closed, but this is not what I'm talking about.)

[FW]

There are several ways to get gas before going that far. "Valving" a freeflowing reg is the simplest (in sidemount anyway). When I took my basic OW class, we had to do a "broken regulator" drill. You can even breathe directly off the tank valve, if it meant saving your life.

No, I have never tried changing regs underwater, but I just might try it on one that is due for overhaul anyway. As you know, not all regulators have the same mechinism in the 1st stage, and some would be a lot harder than others to clear.

[Scott]

I have read reports of it being part if sidemount classes in Mexico and of people doing it, but I have never seen it done in person.

Scott

[EEL]

Russell,
Sidemount divers can access the gas in the independent cylinder by feathering the valve on and off to breathe. This would be next to impossible with independent backmount. Yes I have practiced this and there is a rhythm that you get into. I can even scooter with left or right hands and feather with the other, but it helps if you know the cave well.
I would hopefully never consider switching regs underwater, but I know Andrew has practiced it in the pool. I will let him comment on how plausible it really is.
Dive Safe,

[mpoucher]

I've done it during deco when my deco-bottle reg failed. I would exhaust all other possibilities first, especially with DIN - nothing is more frustrating that a din valve that just won't start - imagine that while holding your breath! Oh, and remember to re-build the reg's IMMEDIATELY! Don't forget for a few weeks for it to turn green and remove all the chrome on the inside.

[Greenwood_60]

If it was fresh, clean, spring water, wouldn't you be fine simply running it for a bit to dry it out?

[argyris]

I have done it once as a practise (I have 3 cylinders) and it is not as easy as it seems. Some regulators will be very hard to recover from the water entry. The presure gauges will be flood also. As I recall UK divers seems to have done it effectively in the past. I think this is a very desperate technique.

[DA Aquamaster]

If it was fresh, clean, spring water, wouldn't you be fine simply running it for a bit to dry it out?

It depends on the design of the regulator.

1. With a flow thru piston design like the MK 10, Mk 25, etc, it would probably be adequate, with the possible exception of the HP ports, but those are easy for the diver to access on their own.

2. With a flow by piston design like the Mk 3, Mk 2 Plus, etc, there is a small hole that allows air to pass to the compression chamber above the piston. However, ther eis very little exchange of air between the compression chamber and the rest of the reg, so once water got there it would be very unlikely to be removed by flowing gas through the reg, especially in on long purge.

3. Diaphragm regs are also more likely to have dead spaces where water may not be easily purged from the reg.

[DA Aquamaster]

There are several ways to get gas before going that far. "Valving" a freeflowing reg is the simplest (in sidemount anyway). When I took my basic OW class, we had to do a "broken regulator" drill. You can even breathe directly off the tank valve, if it meant saving your life.

The vast majority of regulator failures are of the "fail open" variety where feathering the valve will work well. I have even seen a MK 5 continue to function with a broken mainspring.

The exception to this would be events where the lever in the second stage is blocked by an object that then prevents the lever form opening the valve, or if for some reason the poppet (or shuttle valve) in the regulator is able to jump past the tabs on the lever. This is realistically only likely to happen on a balanced second stage and again either requires a damaged lever, or a foreign object under an arm of the lever that allows it to be lifted enough to release the poppet. And to be fair I have only seen this occur on a single regulator in about 15 years of servicing regulators.

[cavermatt]

I am glad I have 200 bar Din Valves on my tanks... 300 Bar valves take too long to screw in when I can breathe!