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

[oxyhacker]

We looked into this when we were working on the reg book, and were told by several reg manufacturers that so-called balanced 2nds are not perfectly balanced, for this reason and others, so that as the pressure increases they will gradually begin to leak. This will happen at a higher pressure than it will on a non-balanced version, but still at well below the failure point of the hose or other components.

Apeks for example says this should happen at about 300 psi, with the external adjuster turned all the way in to the hardest-breathing position, and that they have never had an complaints or problems reported since they started making the balanced 2nds due to failure to vent.

So without knowing how much higher the reg might have gone if you'd kept cranking up the pressure, and without doing the test on a larger sample group, it's hard to say whether everyone should run out and buy OPVs for their Apeks (or balanced barrel poppet SPs, DRs, Atomics, etc, all which use a similar valve). There are a heck of a lot of these valves out there, and they do not seem to be bursting in any measurable quantities.

 

[PhilEllis]

We looked into this when we were working on the reg book, and were told by several reg manufacturers that so-called balanced 2nds are not perfectly balanced, for this reason and others, so that as the pressure increases they will gradually begin to leak. This will happen at a higher pressure than it will on a non-balanced version, but still at well below the failure point of the hose or other components.

Apeks for example says this should happen at about 300 psi, with the external adjuster turned all the way in to the hardest-breathing position, and that they have never had an complaints or problems reported since they started making the balanced 2nds due to failure to vent.

So without knowing how much higher the reg might have gone if you'd kept cranking up the pressure, and without doing the test on a larger sample group, it's hard to say whether everyone should run out and buy OPVs for their Apeks (or balanced barrel poppet SPs, DRs, Atomics, etc, all which use a similar valve). There are a heck of a lot of these valves out there, and they do not seem to be bursting in any measurable quantities.

Hi Vance. When we discussed this with Apeks, they told us the same thing.....full relief at about 300 PSI intermediate pressure. The problem is two-fold......the inflators seem to open below this threshold and not all regulators are adjusted to the optimum factory settings. We wanted to test a larger population of regulators. To be honest, I didn't feel it was appropriate to pull new regulators from stock and expose them to this much intermediate pressure. We did test a second TX-50 regulator, and the results were approximately the same.

I know divers should be well trained to handle a run-away inflator. My concern is this happening at shallow depths, maybe with a decompression obligation pending, and rising to the surface rapidly due to the limited response time. We did test a fairly large number of the fixed OPVs (about 25 individual valves) and they opened at an average of 205PSI, with a pretty tight distribution. I personally feel that discussion of the OPV being a significant failure point is more theoretical than real. With the o-ring changed annually and maybe even the OPV replaced annually, the potential for failure is very low compared to the risk of the run away inflator. Thanks.

Phil Ellis

 

[Rick Murchison]

Verrrry interesting.
I always put more credence in field test (a la Phil) results than manufacturer's "oughta's."
What this all means to me is that I should check my own regs, tuned the way I tune 'em, then make the OPV decision on a case-by-case basis. My impression is that my Legends will freeflow readily at only moderate overpressures - but we shall see. I'll report after I test 'em (it'll be about a week before I can get around to it as the Lovely Young Kat & I are headed for COZ tomorrow )
Rick

 

[PhilEllis]

Verrrry interesting.
I always put more credence in field test (a la Phil) results than manufacturer's "oughta's."
What this all means to me is that I should check my own regs, tuned the way I tune 'em, then make the OPV decision on a case-by-case basis. My impression is that my Legends will freeflow readily at only moderate overpressures - but we shall see. I'll report after I test 'em (it'll be about a week before I can get around to it as the Lovely Young Kat & I are headed for COZ tomorrow )
Rick

Hi Rick. Unfortunately, the Legend will not blow open any easier than the Apeks. Both of these are fully balanced, not the 99% that most manufacturers attempt to acheive. I think what makes these designs more difficult to blow open the the size of the balance chamber. I look forward to seeing the results you get. Unfortunately, we have "purged" ourselves of all AL products, even our house and used inventory, so I can't do the test myself on a Legend. I would not want to do this test on a customer regulator. Let us know.

Phil Ellis

 

[DA Aquamaster]

This is a really alarming thread.

The industry standard for the last 40 years has been to bias any balanced second stage poppet so that it will still retain a down stream pressure relief function. This is easily acheived by ensuring the area of the balance chamber on the downstream side of the poppet is slightly smaller than area of the orifice acting on the upstream side of the poppet. The principle exception to this has been Posiden's second stage design where there is no possibility of over pressure relief. But Poseiden addresses this design issue by incorporating an OPV into the hose.

It is not rocket science and it is in my opinion an excellent reason to buy something other than an Apeks reg, especially when you consider that a runaway inflation could result in addition to or in place of a burst hose. (Not that a run away inflator is a surprise as many "balanced" inflators also contain a degree of down stream bias.)

In my experience nearly all second stages (balanced or otherwise) will begin to freeflow at intermediate pressures around 170 to 180 psi over ambient pressure. This is well short of the hose's rated pressure, let alone its burst pressure, and is below the pressure where a power inflator would be expected to begin to leak gas into the BC.

With regard to OPV's, I don't think they have a place on a first stage unless you are configured in such a way that a first stage could be isolated from a second stage. For example, I will dive doubles with a FFM in some circumstances where I have two first stages routed to a gas block where the gas is shut off from the first stage not currently in use. Potentially a leaking HP seat in that unused first stage could result in excessive IP and a burst hose over time if the OPV were not present.

OPV's are not complex but they do involve a seat and a spring and the failure of either could result in loss of gas. I see no need to add an OPV with an additiol seat and spring into a system that should already incorporate a downstream biased second stage to vent excess pressure. The solution is not to add an OPV but rather to get a decent regulator.

 

[oxyhacker]

Just a minor clarification. By "valve" in the passage below I meant to be referring to the balanced valve in the 2nd, not the OPV.

There are a heck of a lot of these valves out there, and they do not seem to be bursting in any measurable quantities.

 

[Thalassamania]

I guess I'll have to have my local hydraulic shop make me up some Kevlar intermediate hoses.<G>

 

[ianr33]

Question for those that know a lot more about Regs than I do:

If I check the IP of my regs on a regular basis will that more than likely prevent the possibility of the problems being discussed here,or can the IP suddenly,catastrophically,increase in the middle of a dive?

 

[PhilEllis]

Question for those that know a lot more about Regs than I do:

If I check the IP of my regs on a regular basis will that more than likely prevent the possibility of the problems being discussed here,or can the IP suddenly,catastrophically,increase in the middle of a dive?

Checking your intermediate pressure on a regular basis is a good idea, and can give you an indication of a problem when you start to see some creep in the pressure. But to answer your important question, a high pressure valve can fail catastrohically at any time.

Four years ago, my son and another instructor were down in Pelham, Alabama making a couple of dives. The other instructor had a brand new Apeks TX-100 regulator that had just been removed from the box, tested and adjusted, and placed in service. About 10 minutes into the dive, at a depth of 140 feet, the high pressure seat failed completely and full cylinder pressure was venting from the second stages. So, it can and does happen. Thanks.

Phil Ellis

 

[Greg Barlow]

I will typically check my IP on all my regs during surface intervals, as I keep a small gauge with me while making shore dives. It only takes a few minutes to do so, and gives me a little something to do while offgassing.

Greg Barlow