View Full Version : Over Pressure Valves

Major Clanger
30-12-2012, 04:50 PM
My unit was second hand and came with two apeks first stages for the dil and oxygen cylinders. Neither had OPV's on the first stages. Are they necessary? I've dived most of the year without any but then thought I should. However, I'm now looking to take the unit off the stand but the valves are located in a position that snags whatever the unit sits on and may become damaged. So the qu is, do I need them or not? Never seen other meg users have them but think I should. With the hose run, the opv position is pretty much set in stone.

30-12-2012, 04:58 PM
If your IP creeps up, you could end up blowing a hose without the OPV. I have them on both 1st stages; I have a cylinder boot on the bottom of my can, which gives a bit more space under the 1st stages.

Major Clanger
30-12-2012, 05:04 PM
I thought about using a cylinder boot, cheers.

30-12-2012, 05:13 PM
Do you have a BOV or ADV on there that is a downstream valve?

I'd say you need one on the O2 side. Could you use a manifold to put it elsewhere?

Major Clanger
30-12-2012, 06:11 PM
Think I'm going to keep them on there and work around it. Like the boot idea to give extra room.

Neil Brock
30-12-2012, 06:59 PM
The prime function of a second stage is to breath from !

However, it's often forgotten that its secondary function is to act as a pressure relief valve for a first stage with excesive interstate pressure creep.

Most, ( but not all) second stages are down stream valves so at a given I.p., typically between say 13-16 bar, they will begin to act as an over pressure relief valve for the first stage they are connected to. This usually manifests itself as a slight hiss from the second stage. This is quite simply the rising I.p. overcoming the strength of the spring in the second stage.
You often see people twating second stages when they are hissing or free flowing, but god knows why !
The hiss is (asuming the second stage is set up correctly) a symptom of I.p. creep, where the first stage pressure is rising for some reason. (Faulty seat / faulty or damaged "O" ring etc).

If you have removed the second stage, and all that is left is say a suit inflate, a wing inflate, a dil or an O2 supply, and there is no PRV fitted to the first stage, then eventually, when the pressure gets high enough the low pressure hose might potentially burst, with all the hassle that might encompass. Some dil first stages connected to say a BOV are not an issue as the BOV is effectively the second stage and acts as an OPV.

Temper this with the thought though, that most LP hoses are of reasonable quality and can stand a fair bit of over pressure !

The main issue for some RB's is the extra pressure of gas going to the solinoid, say the O2 first stage being too high, is that it will cause issues for the O2 solenoid open / closing function. Fitting an OPV will help mitigate this to some degree, bearing in mind that the supply gas cylinder might be as small as a 2 litre :p

I hope this refreshes what you probably all ready knew !

30-12-2012, 07:15 PM
Thanks Neil... my thoughts too.. I've got a BOV on mine, but it would still be a worry having gas forced past the ADV.. or a hose blowing. Nothing on the O2 side except my block... I'm keeping my OPV's.

30-12-2012, 09:21 PM
An alternative is to get a set of Tek 3 first stages; all the ports point upwards. A boot is a bit cheaper :)

Major Clanger
30-12-2012, 09:25 PM
Thanks Neil, for a while I had a reg on the O2 side as a shallow bail out option. Will probably put it back on once I've got out the way what I'm doing and the unit goes back on to a stand. Temporarily taken off, to reduce travel weight.

31-12-2012, 07:46 AM
My Meg had OPV's on and as far as I am aware they come as standard with a new unit, so would recommend keeping them :)

07-01-2013, 12:11 PM
I've Cyklon 1st stages on my unit, I'm assured that these 1st stages have built-in OPV's in them......

Couldn't you raise your cylinders on the unit by dropping the cylinder mounts to get the clearance you need for the OPVs?