Opening Tank Valve

[Scuba Client]

Hi All - my recently purchased Scubapro Mark25 Evo reg still says in the manual to gently purge the second stage when opening the cylinder. I thought that practice was now obsolete - would appreciate any guidance. Thanks

I always open my valve slowly. A good habit when using O2. And yes, I press the purge gently.

 

[mallbritton]

This is the method I do when turning on the air on a tank. I press the purge valve on my primary and gently open the tank valve and turn it all the way open.

 

[Hojo in SC]

I was taught in school to slightly open a tank to blow the dust off.

 

[60plus]

You should always open a valve very slowly to prevent shocking and therefore damaging / rendering inaccurate your tank contents pressure gauge. All components in regulators and gauges have inertia and momentum and opening a valve too fast causes the rush of air / gas results in excessive acceleration and / or deceleration forces on those components.

 

[Subcooled]

... to gently purge the second stage when opening the cylinder. I thought that practice was now obsolete

And why would you think that this practice is obsolete?
- because nitrile rubber o-rings suddenly changed their characteristics?
- because physics just changed?

I have experienced a fair amount of o-ring failures when pressurizing my cylinders. Somehow (unscientifically) I feel that slower pressure increase is more gentle to those rubber parts.

 

[Subcooled]

All components in regulators and gauges have inertia and momentum

Yes, they have inertia, as do all matter (=with mass) in the universe.

They do however not have momentum as their relative speed/angular speed is zero.

All the rest is correct.

 

[Wibble]

Pointless. Right up there with quarter turn back on the valve.

Need to disagree with you on this.

Turning on oxygen rich/pure oxygen mixes can create an oxygen fire with the hammer effect. Easier to turn all cylinders on slowly.

Quarter turn back means that changes in ambient pressure or temperature won't jam the valve open. Yes, the damn twinset RH valve was jammed for me where I couldn't reach behind to turn it off (during an underwater test); needed a proper turn off on the surface.

But do carry on.

 

[TMHeimer]

Need to disagree with you on this.

Turning on oxygen rich/pure oxygen mixes can create an oxygen fire with the hammer effect. Easier to turn all cylinders on slowly.

Quarter turn back means that changes in ambient pressure or temperature won't jam the valve open. Yes, the damn twinset RH valve was jammed for me where I couldn't reach behind to turn it off (during an underwater test); needed a proper turn off on the surface.

But do carry on.

Hmphh.. That's a different take on why quarter turn back may be useful. Is it possible there is a defect with your RH valve? I'm not familiar with twins, but can't see that a quarter turn back (or less than that as I do) can really hurt anything. Now maybe if you consider boat DMs fooling with your valve to make sure your air is on and mistakenly turning it off. Not a concern if you take 3-4 breaths before jumping in or are diving solo from shore.

 

[Wibble]

Hmphh.. That's a different take on why quarter turn back may be useful. Is it possible there is a defect with your RH valve? I'm not familiar with twins, but can't see that a quarter turn back (or less than that as I do) can really hurt anything. Now maybe if you consider boat DMs fooling with your valve to make sure your air is on and mistakenly turning it off. Not a concern if you take 3-4 breaths before jumping in or are diving solo from shore.

A DM -- or anyone else for that matter -- touching my kit would result in me throwing them over the side! Thankfully we don't have DMs on our boats, just independent divers who are responsible for their own kit and welfare. (Maybe that sounds a tad strong, but a boatload of essentially solo divers are like that -- touch their kit at your peril!)

I think it was against the end-stop and in the warmer ambient temp topsides, the valve contracted in the colder water and jammed. When reaching back over one's shoulder, you don't have much purchase to turn the valve, certainly not as much as when you're standing in front of the valve.

For me it's just logic that you open a valve fully, then back it off a smidge, say 1/8th or 1/4 turn. When doing a shutdown, you've drilled it into your muscle memory which way to turn the valve for off and on.

I'm not keen on the other advice which is to only partially open the valve. There be a load of potential problems, like not opening it enough to breathe when you're deep.


I always, like OCD always, test my breathing gas three times. Firstly when standing in front of the kit when I'll turn the gas on both sides, then breathe from each regulator and check the pressure. Secondly when I've got into the kit and put the necklace on -- breathe from it -- and routed the longhose around -- then breathe from it at least three breaths. Finally as I get up to waddle over to the jump I'll always breathe from it for another three breaths (and ensure there's gas in the wing).

The same applies with a rebreather, but in this case it's the pre-breathe to ensure the scrubber's woken up. Even so, before I waddle over to the jump it's check the PPO2 (oxygen levels) and some gas in the wing.

Critical to know that you can breathe when you jump, and that you will float on the surface. Was on a boat once where somebody died because they didn't ensure that.

 

[Bob DBF]

Turning on oxygen rich/pure oxygen mixes can create an oxygen fire with the hammer effect. Easier to turn all cylinders on slowly.

And it doesn't need to be pure O2 to get the diesel effect, although there probably will be less damage

That's a different take on why quarter turn back may be useful.

For me it's just logic that you open a valve fully, then back it off a smidge, say 1/8th or 1/4 turn.

Until the modern era, when everyone should dive and learning by catchphrase was the standard, it was explained that one need only back the valve off from engaging it's limit of travel slightly, as @Wibble describes above.

1/4 turn was never necessary, and with the faster opening ( less turns from shut to fully open ) it becomes more problematic as a valve open check will give no deflection on the SPG when the valve is 1/4 turn open. Despite this, 1/4 turn back continues to be the litany.