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.