OPV valves for deco regs?

[DANDM]

I'm setting up my first regs for a deco bottle and I wanted to ask about over pressure valves - OPVs. I've seen some people have them on their deco regs, but not all. Some brand new deco regs seem to include them and some don't.

My questions are:
- What is their purpose on deco regulators?
- Should all deco regs have them? Or is it dependent on the model of the regs or another variable?

I understand it's useful for like argon bottles, but with a second stage are they actually necessary?

For reference, I've recently purchased a second hand Scubapro mk17 1st stage, apeks xtx200 2nd stage, 1m hose and a brass SPG on short hose. They're currently getting serviced for O2.

 

[gschaut]

Most regulators use a downstream valve in the second stage. This prevents overpressure in the low pressure hose between 1st and 2nd stage. Many divers using Argon suit inflation will have OPV valve screwed into an LP port in the first stage. If for some design reason your 2nd stage does not open or "leak" when LP hose is over pressured, you can add OPV valve onto any LP port on the first stage.

 

[PfcAJ]

Not needed.

Don’t use upstream 2nd stages.

 

[MyBuddy]

You’d only need an OPV on the first stage if you’re going to use in line shutoffs on your second stages. If those are recommended I cannot say but some very experienced people have been known to use them.

 

[andrespp]

My BO tanks are provided with regulators with a shut off device in the second stage. So had to place OPV of the first stages in order to provide relief to a potential increase of the IP. My preference is to have the valve tank open and the shut-offs closed during the dive, as this prevents both freeflowing as well as flooding inside the regulator and SPG.

 

[andrespp]

My BO tanks are provided with regulators with a shut off device in the second stage. So had to place OPV of the first stages in order to provide relief to a potential increase of the IP. My preference is to have the valve tank open and the shut-offs closed during the dive, as this prevents both freeflowing as well as flooding inside the regulator and SPG.

One word of advice: if you need to BO, prior to put the shutoff device in the open position, hold it with a hand and press slightly press the purge button of the 2nd stage , THis will prevent the sudden hammer of the pressure damaging the 2ns stage.

 

[mr_v]

Many things depend on the type of diving you do, the way you were taught, and your personal preferences.

In multi-tank bailout scenarios, my non-primary bailouts have OPVs on the first stages because I use shut-off valves. The non-primary bailouts are charged and closed. The shut-off valves keep intermediate pressure between the first and the second stages, so that the reg does not become loose. The configuration also prevents unexpected gas loss if any of the non-primary bailout second stages bump against the environment.

My deco regs are configured like the non-primary bailouts with OPVs and shut-off valves.

The primary bailout does not have an OPV or a shut-off valve. If the primary first stage craps out during the dive, it will "fail to open" and the second stage will start freeflowing. There are emergency procedures for dealing with that scenario.

There are several things that you should consider.

First, OPVs and shut-off valves introduce new failure points. OPVs are cheap to replace, so if mine is flowing, I'll replace the OPV if my intermediate pressure is within the expected range. Sometimes OPV flow because they do their jobs, so you must check the intermediate pressure to ensure that it is not the first stage's fault. Always bring a few spare OPVs if you use them and have an IP gauge.

Second, shut-off valves are wonky. They'll start leaking at some point which means they won't hold the pressure between turned off first stages and second stages. You can rebuild these valves for less than 25 cents. I usually rebuild them whenever I see small leaks. I also use O-rings that are softer than the ones specified as they seal better; downside - I must rebuild more often.

If you go the OPV/shut-off valve route: it is okay to get a $5 OPV but please spend $ on a decent shut-off.

YMMV

Cheers~

 

[Agro]

Some people use shut-off valves, for ex. mr-v. I do not and I do not see any reason to do so.

Yes, if you use a shut-off valve then you must add an OPV. You MUST.

If you use first stage only for argon then you must add an OPV.

Second stage is an OPV. So if you have a functional (without shut-off valve) 2nd stage, no OPV is needed.

I use XS Scuba Standard OPV - Over Pressure Valve - Brass — XS Scuba - Everything For The Perfect Dive and never ever had any problems. I use serveral of them (argon, booster, workshop), no failure within 10 years.

Special case Poseidon. Some Poseidon regulators (not all of them) are upstream, this means 2nd stage is not an OPV. In this case you need an OPV at any time. Some Poseidon first stages (not all of them) have a built-in OPV. Some old ones had the OPV in the LP hose.

You may use a Poseidon first stage with built in OPV as argon inflator. No additional OPV needed.

 

[grantmac]

A Poseidon 3960 makes a fantastic suit inflation reg with built in OPV and very robust.

 

[rjack321]

In-line shut offs on deco regs are not needed and just one more thing to go wrong. Which then saves adding yet another failure point - the OPV. OPVs are probably the single most failure prone thing we use in scuba diving - the only thing which fails more often is brains (narcosis, CO2, poor choices on the surface too).