transferring scuba regulator from tank to tank underwater?

[Doc]

Whatever happened to that old SCUBA Parlour Trick we used to teach....

Breathing right out of the stem of the bottle, feathering the valve?

Maybe that was "the answer" he was looking for.

 

[Shcubasteve]

Here's a thought ........

Is he a fan of Oceanic gear?

The oceanic DVT has a little piston that closes off the first stage. It won't flood when taken off a tank underwater. Cracking the good tank to blow out the little bit of water between the tank and the reg and it might do it.

To my knowledge, oceanic is the only one with this little piston inside the yolk fitting.

FWIW- Aqualung Legend has an Auto Closure Device in the 1st stages of newer models that keeps water out on the surface... Unlike the oceanic dvt, the legend is held open by contact with the cylinder valve, not air pressure.

 

[halocline]

And why do you think an unbalanced piston is any better then any other design???
I just don't get where some of these opinions come from.

The reason an unbalanced piston reg with an unbalanced 2nd stage is more tolerant of flooding is because there are no balance chambers to get flooded, and the piston stem o-ring is not subjected to the higher pressure gradients associated with balanced piston regs. In short, the intrusion of water into the first stage will not cause as much damage as it can with a diaphragm reg, or even with a balanced piston, although a BP would be more tolerant than a diaphragm due to the presence of a balance chamber in the dry section of a diaphragm 1st stage.

That's where this opinion comes from, please feel free to argue against it if you have a differing one with some reasoning to support it.

Awap's idea about holding the first stage inlet pointing down to trap the air in the reg is a good one, I didn't consider that. You'd almost certainly get some water in the first stage, but probably only a little.

 

[Doc Harry]

I've seen it done twice, under a slightly different circumstances.

Both times there was big leak from the yoke o-ring that couldn't be corrected by traditional methods. The DM removed and replaced the yoke underwater to stop the leak.

Did he do it without flooding the first stage? Dunno.....

 

[fppf]

The reason an unbalanced piston reg with an unbalanced 2nd stage is more tolerant of flooding is because there are no balance chambers to get flooded, and the piston stem o-ring is not subjected to the higher pressure gradients associated with balanced piston regs. In short, the intrusion of water into the first stage will not cause as much damage as it can with a diaphragm reg, or even with a balanced piston, although a BP would be more tolerant than a diaphragm due to the presence of a balance chamber in the dry section of a diaphragm 1st stage.

That's where this opinion comes from, please feel free to argue against it if you have a differing one with some reasoning to support it.

Awap's idea about holding the first stage inlet pointing down to trap the air in the reg is a good one, I didn't consider that. You'd almost certainly get some water in the first stage, but probably only a little.

Granted the designs are different. However, I don't see anything in any one type of design that would make it more or less tolerant to water. Having a "Balance Chamber" or not would not have any effect on the parts when water is moving through them. What would effect the design is the flow paths. How much straight distance is between parts. Is there a direct line to a soft part. Water backed by gas can be abrasive at high velocities. So its a question of what, where, and how fast the water is going to hit.

Seeing that there all scuba regulators, I'm sure the designers take into account the possibility of water intrusion. They know how the diving public really treats there gear. But it would be an interesting experiment to soak a bunch of regs, put them on a tank, and turn the valves on as fast as possible.

The speed at which the valve is turned on in my mind is the biggest issue. If you just slam the valve on your going to generate much higher velocities then if you just ease the valve on.

 

[halocline]

Of course having a balance chamber affects the water tolerance of regulators. And, as you mentioned, the "flow paths" (or more specifically, where the water would/could go) is different for different types of regulators. In a diaphragm 1st stage design, the HP area surrounds the balance chamber, which is filled with air at IP. If water under high pressure forced it's way into the balance chamber and compromised the o-ring seal, it would result in immediate and severe IP creep, quickly causing uncontrolled freeflow. Balance chambers use tiny little o-rings and small volumes of air, which work great when they're dry, but are much more susceptible to failure when they're wet. A very small volume of water could cause something like "hydrolock" in which case the seat would not budge unless water was forced out. In the second stage, the balance chamber is "pushing" the poppet closed with IP. If that flooded you'd have an incompressible force holding the poppet closed; the only way it could open would be to force water either out the balance chamber o-rings or back upstream through the hole in the seat. I honestly don't know exactly how that would work out in a real life situation, but I'd probably rather find out in a bucket than at depth.

The balanced piston design, and by this I mean the flow through (SPMK5 et al) design, could only send water up through the piston into the IP chamber. (and the HP port, but that;s the same in all regs) If, however, there was enough hydraulic pressure in the HP chamber, it could easily rupture the HP piston stem o-ring, which would cause an immediate and severe HP leak into the ambient chamber. The reg would still work (IP could be maintained) but you'd have a pretty nasty leak.

The unbalanced flow-through piston does not have either of these scenarios. The only place for water to go is up through the piston; as soon as IP is reached, the seat cuts off flow, shielding the piston stem o-ring from HP air.

For second stages, if you just have a simple downstream, "puck" seat design, water would go through the orifice, into the air barrel or reg body, and you be breathing water until it got flushed out; almost certainly just a few CCs. But there's nothing else it could damage.

This is one reason that the SP MK2 makes an ideal pony or stage reg; if the reg were depressurized at depth and water migrated from the 2nd stage to the 1st, you can easily just blow it back out.

 

[fppf]

So to summarizes your post, you believe that
A) water in the "balance chamber" will damage the o-rings
B) water in the "balance chamber" can cause a hydraulic lock up

The only way o-rings or seals can be damage is by having high velocity liquid driven by gas blasted across it. So all the o-rings that are in groves wont get direct force. The clearance for o-rings sealing gasses is much tighter then liquids, so its ok there as well. Pretty much the only seal at risk is the high pressure seat, which is common in all designs.

As for hydraulic lock up, you need a sealed system full of liquid to get a lock. There is no totally sealed area in the regulator of any design that this can happen to. And even if there was, I don't see total liquid intrusion filling all the voids. The high pressure area has the hole compliance of the cylinder to back into. The balance chambers are linked to the low pressure side so as soon as the 2nd stage starts flowing it would unlock as well, if it could ever lock. Same thing goes for the second stages.

One thing that would be effected would be the response of the regulator until the liquid started clearing out. The liquid in the balance chambers would cause a spring rate change of the balance chambers.

As a side note, hydraulic regulators share some of the designs of there gas counter parts.

It would be an interesting test to take a few different types and mfgrs of regulators and test them a few times. Then tear them down and inspect for any abnormal wear.

 

[halocline]

So to summarizes your post, you believe that
A) water in the "balance chamber" will damage the o-rings
B) water in the "balance chamber" can cause a hydraulic lock up

The only way o-rings or seals can be damage is by having high velocity liquid driven by gas blasted across it. So all the o-rings that are in groves wont get direct force.

I said it "could" damage the o-rings, not that it "will". It's a matter of likelihood of compromising the small seals that keep HP air out of the balance chamber.

High velocity liquid being forced across o-ring sealing surfaces is exactly what is likely to happen when you have significant water in the 1st stage. You have no idea what the specific forces on particular o-rings would be in that situation, neither do I. I simply stated, and fully explained my statement, that unbalanced piston first stages are likely to be more tolerant of being flooded. This is a commonly accepted assumption by knowledgeable regulator technicians. I'm not sure why it bothers you so much.

 

[fppf]

It does not really bother me per say.
But "knowledgeable regulator technicians" in the scuba industry most likely means someone that took a one day class from a sales rep and can follow a manual. And there making assumptions on things they don't understand. That is what really bothers me, unfounded spread of information based on opinions not facts. And I'm not saying all techs are monkeys either.

But there is no true information or testing that would provide a sound answer. So making a statement that one is design is better then another just because some guy said so seems a bit of a stretch.

The size of an o-ring does not make it any less durable then a large seal. Actually a small seal has less area and thus less actual force applied to it.

 

[vshearer]

I'd like to see a [-]tank[/-] reg explode.