Diving Truth or Myth

[gerbil]

When turning on your air turn it on full and then back a half turn

If so why? If not why not?

[SilvaFish]

I have been told that turning the valves the other way half a turn prevents the valves from jamming open. Whether this is true or not, I don't know as never had the problem! I just do it now out of habit.

[Scuttler]

Originally Posted by SilvaFish

I have been told that turning the valves the other way half a turn prevents the valves from jamming open. Whether this is true or not, I don't know as never had the problem! I just do it now out of habit.

Same here

[weazelz]

I assume it's to de-stress the valve after an over-enthusiastic novice opening

I tend to open mine fully, but gently for the last bit. especially on a twinset where I don't want any confusion on which way the knob turns

[Hickdive]

It's an old engineers thing, turn the valve back and anyone trying to turn it to check its status will know that it is open and not simply jammed shut, so they won't apply excessive force trying to open an already open valve, possibly damaging it or jamming it open.

A quarter turn back on a decent cylinder valve won't affect the amount of air coming through but some people have said that, although the turnback wasn't detectable on the surface, it was noticeable at depth. You pays your money and you takes your choice, I quarter turn back, ymmv.

[gerbil]

That was the logic given to me when i first learnt and even today if i turn the tap on in the bath i turn it on full and then back. Its just that when i was in the bath doing just this i wondered if i was barking mad?

[Scuttler]

Originally Posted by gerbil

That was the logic given to me when i first learnt and even today if i turn the tap on in the bath i turn it on full and then back. Its just that when i was in the bath doing just this i wondered if i was barking mad?

Nah....one of my taps used to sieze if you opened it fully.....then I changed them

[Sparky]

I find it's now second nature to turn them on fully and then do a half turn back, Now i'm on twins I was told to have the isolater all the way on so if you need to turn it off in a hurry you don't waste precious time turning it the wrong way.

[dry suit diver]

Originally Posted by Hickdive

It's an old engineers thing, turn the valve back and anyone trying to turn it to check its status will know that it is open and not simply jammed shut, so they won't apply excessive force trying to open an already open valve, possibly damaging it or jamming it open.

A quarter turn back on a decent cylinder valve won't affect the amount of air coming through but some people have said that, although the turnback wasn't detectable on the surface, it was noticeable at depth. You pays your money and you takes your choice, I quarter turn back, ymmv.

wot he said
and on fluid control valves of a certain design it destresses the internal workings. not that you would be breathing fluid from a cylinder


I have never noticed a difference in breathing with vales fully open half qtr etc inluding manifold, in fact the manifold isolator is open just over half a turn as it give me a quick shutdown

[nickb]

Hickdive's spot on. I remember being told to do this by the old hands when I was a young apprentice. Generally this applied to valves that were left permanently on.

I did this with my cylinder valves for years by force of habit, but admit that when I flirted briefly with DIR-type stuff and read that they recommend (mandate?) turning valves fully on, I did so for a while. On a 6m stop, I was was practicing shutdowns, in the half-arsed way I used to, and found I couldn't shift one of the valves: it was jammed open. Now I turn the valve back a touch, not even a quarter of a turn, but enough to prevent it jamming open.

My manifold isolator is only a half to one turn open though; I know which way a tap turns on and off as I've been doing it all my life