does anyone use OPV's ( over pressure valves ) on their primary 1st-stages ?

[scubafanatic]

...... I understand the traditional useage of OPV ( overpressure valves ) with respect to deco/pony bottles, however, what is the recommendation with respect to the usage of OPV's on 'regular' 1st-stages..... ie., primary regs that are dove frequently ?

There's a new thread here indicating it's a good idea to so, to avoid a potential LP hose 'blowout' if a HP seat gives way.

Is there any downside to installing an OPV on a primary regulator ? ...or does such a device simply add another failure-point ?

...also, how does one adjust the IP as which the OPV releases/vents excess pressure, and how does one decide exactly what is an appropriate 'yield' pressure ?

...among my regs are a pair of 'overbalanced' APEKS XTX 200's...... would it be possible to dive deeply enough to have such an overbalanced 1st-stage 'boost' the IP to such an extent it would 'blow' the OPV's ?

Thanks,

Karl

 

[lamont]

your second stages should act as an OPV. you need OPVs on argon bottles since you don't want your drysuit inflator to act as an OPV.

 

[scubafanatic]

Hi Lamont,

..not according to this :

Originally Posted by loosebits
Hmm, wouldn't the 2nd stage, balanced or not, free flow and relieve the pressure before any hose ruptures? Should I stick an OPV on my left post's 1st stage?

I've never heard of anyone using OPV's on anything but DS inflation bottles where no 2nd stage is present.

No, not always. A balanced second stage (newer ones esp.) that are truly well balanced will sometimes hold back an IP of over 300psi which with a hose rated to 250psi (common rating) could be a problem. Not so much with a brand new hose but one a few years old can significantly lose its ability to operate over rated pressure.

(this quote is from yesterdays Zeagle back up reg system thread )

Karl

 

[JeffG]

Hi Lamont,

..not according to this :

Originally Posted by loosebits
Hmm, wouldn't the 2nd stage, balanced or not, free flow and relieve the pressure before any hose ruptures? Should I stick an OPV on my left post's 1st stage?

I've never heard of anyone using OPV's on anything but DS inflation bottles where no 2nd stage is present.

No, not always. A balanced second stage (newer ones esp.) that are truly well balanced will sometimes hold back an IP of over 300psi which with a hose rated to 250psi (common rating) could be a problem. Not so much with a brand new hose but one a few years old can significantly lose its ability to operate over rated pressure.

(this quote is from yesterdays Zeagle back up reg system thread )

Karl

No Lamont had it right.

 

[in_cavediver]

Hi Lamont,

..not according to this :

Originally Posted by loosebits
Hmm, wouldn't the 2nd stage, balanced or not, free flow and relieve the pressure before any hose ruptures? Should I stick an OPV on my left post's 1st stage?

I've never heard of anyone using OPV's on anything but DS inflation bottles where no 2nd stage is present.

No, not always. A balanced second stage (newer ones esp.) that are truly well balanced will sometimes hold back an IP of over 300psi which with a hose rated to 250psi (common rating) could be a problem. Not so much with a brand new hose but one a few years old can significantly lose its ability to operate over rated pressure.

(this quote is from yesterdays Zeagle back up reg system thread )

Karl

This was posted in reference to a regulator that did not automatically get used. IE an pony reg or a the left post on a set of doubles that you do not normally breathe while underwater. If you are breathing the reg, it would most likely free flow.

That said, I am still not convinced that the IP would creep past burst pressure without free-flowing the reg. Remeber, the LP hose has a rated pressue and a burst pressure. The rated pressure is its intended max daily service pressure and on my hoses, its 250psi. The burst pressure is higher and its an average over the set of hoses tested. The exact burst pressue is unique to each hose, some go higher, some go lower.

 

[O2BBubbleFree]

OK, I understand the OPV on a drysuit bottle. You don't want a runaway inflation. Simple.

WRT a regular 1st, if you have a HP seat fail and your 2nd doesn't freeflow, then something is going to blow (the OPV if you have one or the hose if you don't).

Does it really matter which? Either way your reg is unusable, so that shouldn't be an issue.

I guess you could check to see which one is more expensive to replace, if you're on a really tight budget.

But it looks to me like the OPV is just another potential point of failure, without any added value.

On the other hand I suppose I would prefer an OPV failure. If you are in the 'all else has gone wrong' state, then you could capture and breath the gas coming out of the OPV (like breathing directly off of a tank), but it might be hard to catch and breath off of a blown hose? Maybe those trained and experienced in breathing off the tank can comment here.

 

[lamont]

If your second stages are de-tuned so much that they don't blow then your inflator will go before the hose goes. The lesson is to not detune your regs that much.

 

[tstonedvr]

A thread discussing this was up awhile back on The Decostop. On overbalanced regs such as the Apeks it was possible for the second stage to not act as a OPV and that a OPV would be a good idea on overbalanced regs.

 

[rjack321]

Hoses normally have a burst pressure about 4x the rated pressure. This is not specific to the scuba industry just a typical engineering safety factor.

Lamont had it right in post #2, the hose will never see 800-1200 psi and burst. The 2nd will be venting.

 

[PhilEllis]

That said, I am still not convinced that the IP would creep past burst pressure without free-flowing the reg. Remeber, the LP hose has a rated pressue and a burst pressure. The rated pressure is its intended max daily service pressure and on my hoses, its 250psi. The burst pressure is higher and its an average over the set of hoses tested. The exact burst pressue is unique to each hose, some go higher, some go lower.

I posted this information on a DecoStop thread several months ago, but I am unable to locate the thread. I will repeat what we found when we tested an Apeks regulator.

We took an ATX-200, with an Apeks ATX100 safe second installed, and put it on our test bench. The second stage was "normally" tuned and the regulator was performing as would be expected for normal diving. The diver-adjustable cracking effort knob was turned one full turn from the easiest opening position, and the opening effort was measured at 1.2 iniches of water. We installed one of the industry standard inflators (ours came from a Dive Rite wing)
to determine the level of safety (or lack of safety) of having high intermediate pressure on a balanced second stage. The results were something like the following.

We increased the intermediate pressure in increments of 25 pounds. We moved the pressure up to 275 psi before the inflator began to "auto fill". At that point, we removed the inflator to determine when the Apeks second stage would open. At 400 PSI, I decided to terminate the test due to other unknown possible safety concerns with the test. At the time of termination, the Apeks second stage had still not opened and provided relief for the pressure. I repeated the same test with an inflator from a ScubaPro jacket. That inflator opened at a pressure of about 250 psi.

Our conclusion was that a diver, using an Apeks regulator set-up, should certainly have some sort of provision for high-pressure seat failure. Our conclusion was that a spring-tension, non-adjustable OPV would be the best solution. These types of OPVs present very little actual practical potential of failure, are extremely low profile, and are not terribly expensive. Of course, you could also use an un-balanced second stage, of some other make and model, as a back-up regulator to accomplish the same thing.

The risk of an inflator "runaway", all of the training and reaction to problems of this sort aside, is much too large, in my opinion, to dive these units without an OPV. There will clearly be some dispute from many with regard to our conclusions, and that is OK. We also represent a fairly intelligent group of divers here at our store, and my IMMEDIATE reaction was to put OPVs on ALL of our personal Apeks first stages. The link below will take you to the type of OPV we used and the type we most often sell.

OPV Valve - 200 PSI Pre-Set Pressure Relief

Go to the bottom of this page for the OPV.
Thanks,

Phil Ellis