Full on, and a little off

[Darkforeboding]

I have heard the some of the early scuba valves had a tendency to jam if they were left in a full on position and this was the origin of this technique. I do not know if this was actually the case but the method was taught for many years. At this time most of the diving agencies have changed their recommendation to full on, no need to jam it against the stop but turned on all the way.

That is the way I remember it, too. I was not only told this about a scuba tank but about valves in the engine room in the Navy. Unless the valve is meant to be throttled to control flow, the valve should be opened fully, then closed a little so that it is not forced against the valve backseat if the temperature changes and the metal of the valve expands or contracts.

DFB

 

[markmud]

I've no doubt you are correct with regard to valves on ships; however, the poster who described this as a reason for a turn back was referring to scuba cylinder valves, hence my question.

Hey Hickdive,

Yeah, sorry if I got long winded in my last post (it is a character flaw). HOWEVER, I did write a paragraph that agrees with your quotation above! I agree with you! I don't understand how his post about galvanic action was germane to the topic.

As far as the on or off battle goes, unless you are cave diving where a rocky overhead may contact your valve, I don't think it matters because someone will screw it up whichever way you have it. Take responsibility for yourself, don't let a DM rig your gear, and be prepared if you screw-up with a contingency plan.

DMs who don't listen to me when I tell them to leave my sh*t alone, will sometimes scowl a little when I completely re-rig my gear after they supposedly did it for me.

Do it your way and take responsibility for your actions.

Question: Why are cave divers going into confined spaces with no guard on their tank top (guard on their valve and first stage reg)? It does not seem smart to allow a rock ceiling and your valve/regulator to have unprotected relations.

markm

 

[Darkforeboding]

In some applications there is a reason for the quarter turn back from full open. In applications where the valves are open for long periods of time and or exposed a nasty environment, steam and chemical lines come to mind, the quarter tun back help keep the valve from seizing to the back stop.

Scuba valves do not fall under either of these conditions.

But they are prone to large temperature changes, either because they were taken from 90-100 degree air and put in 70 something degree water (ideal condition) or they were taken from a nice warm room or car into an ice dive from 70 degrees to 32 degrees, or maybe even just the cooling effect of 3000 psi air being lowered to 500 psi in the course of the dive.

 

[PfcAJ]

Question: Why are cave divers going into confined spaces with no guard on their tank top (guard on their valve and first stage reg)? It does not seem smart to allow a rock ceiling and your valve/regulator to have unprotected relations.

markm

Because its not needed. Plus more stuff back there is just more stuff to get entangled and impede access to the valve when needed. The reality of it all is that with even mediocre technique, ceiling contact is minimal and low-energy.

 

[markmud]

Because its not needed. Plus more stuff back there is just more stuff to get entangled and impede access to the valve when needed. The reality of it all is that with even mediocre technique, ceiling contact is minimal and low-energy.

Thanks for your response PfcAJ,

Other posters have mentioned Sheck Exley's predicament where his valve was slowly ratcheted off by contact with the cave (I hope I understood what they wrote). Others have stated that they two-block their valve in the open position to prevent an overhead from turning off their valve.

So why is a guard not needed? I understand the KISS theory (Simplex very sigilum, lex parsimony, Occam's razor, and murphy's law) and that a guard could create resultant issues. Should a diver do a quantitative and qualitative risk analysis regarding a particular dive plan and the decision to use or not use a guard? Is a blanket rejection of a guard reasonable for all situations?

thanks,

markm

 

[Trace Malinowski]

Don't hit the ceiling. If you do, flow check your valves.

If you anticipate that your valves will strike the ceiling frequently due to the distance from floor to ceiling, maybe switch to sidemount.

 

[PfcAJ]

It IS possible to roll off a valve as you describe. I've done it passing restrictions. This is mitigated by always confirming the position of the valves after any contact with the ceiling. Much has been learned from Sheck and since his passing.

I would advise against any mechanism that locks the valve into position. It needs to be able to be shut down quickly in event of an issue.

I'm no stranger to small cave (by backmount standards) or scootering, and I've yet to have a need for a guard. This experience firmly plants a valve guard into the "unneeded" category, and I view it as adding equipment to solve a skill problem.

 

[OkByMe]

Turn the valve open all the way against the stop. The valve "back-seats" to seal the stem from leaking. I don't why that 1/4 turn was started in the first place... It is self evident that the valve is open if it is back-stopped and there is pressure in the hoses. Push in the purge after checking the valve and if gas continues to spill the valve is open all the way, if not, the valve is closed... simple.

 

[Nemrod]

Turn the valve open all the way against the stop. The valve "back-seats" to seal the stem from leaking. I don't why that 1/4 turn was started in the first place... It is self evident that the valve is open if it is back-stopped and there is pressure in the hoses. Push in the purge after checking the valve and if gas continues to spill the valve is open all the way, if not, the valve is closed... simple.

Because you can punch the purge a few times and unless you look at your spg, you will not know the valve is off.

It has been explained by several people why the practice is common. It is not just SCUBA, it is a common practice with compressed gas valves.

In the day before single hose regulators, double hose regulators had no purge valves and in that time as well, we did not use spgs commonly. We turned the valve on fully and then we backed it off a bit. And it was not considered cool to check a valve without asking once it was acknowledged ON.

Aside from forgetting to turn it on, do gooders and DMs checking peoples air on is the most likely way to have the air not on when you hit the water. Of course nowadays, I do a final check after working my way through the maze of do gooders, deck hands, DMs, strangers all checking air on, if the needle drops with each breath or even fluctuates more than a hair, something is not right.

BTW, tanks equipped with J reserve valves, you may well see a needle fluctuation with an spg when the reserve is set on.

N

 

[bakodiver391]

I'm going to continue to open my valves and then back off a smidge. The only way the 1/4 turn can kill you is if you don't know which way to turn a valve, and as others have said, more drills are needed. 35 years as a pipefitter and 30 years diving, I KNOW which way my valves turn.