Turning air off after equipment assembly

[Doc]

Whichever routine you adopt, always take 3 to 4 breaths from your regulator while looking at your gauge just before your dive. If the pressure is steady, you're ready to go.

The best advice overall. This works universally with analog gauges, but some digital marvels can deceive you.

On an analog, watch gauge and suck.

Result 1: If the needle is at 3000 and then shows lower and lower tank pressure after each breath- the tank is off.

Result 2: If the needle is at 3000, but each time you suck, it bobbles noticeably, the tank valve is barely cracked open.

Result 3: The needle doesn't move perceptibly. A good check.

Some Digital gauges can be deceived when they should fail with result #2.

Most modern digital gauges will perceive failure circumstance #1

Test this on your rig, be aware of anomalies.

 

[lamarpaulski]

On boat dives especially I think its best to turn off and purge . I have seen an off tank be mistaken for "on" when unpurged and that could be a big problem and big surprise jumping in. This happens more often than people care to admit as the check on a crowded boat is sometimes not 100% and the gauge reads "full" for first breath or two. People want to be first in water etc..

 

[Colliam7]

My comments probably echo most of the other responses.

In training (PADI), I was taught to turn the air off and to purge the system after equipment assembly if I'm not getting directly in the water.

A reasonable approach. I teach that to OW students as well. It prevents air loss either through a very slow, small leak (e.g. a yoke cylinder O-ring) or having a significant purge occur because something (e.g. someone else's gear) inadvertently cause a purge valve on one of my second stages to be depressed (but not audibly apparent, so it goes un-noticed).

In all honesty, sometimes I do and sometimes I don't. I think the reason for my inconsistency is that I'm not sure I have been given a compelling reason to turn the air off.

The inconsistency is a bigger issue than whether you leave the valve open, or close it. There is no reason to be inconsistent. Either you do it (close the valve) because you were trained to do it, or you don't do it because you don't believe that there is a compelling reason to do it. Frankly, either practice is OK, but the inconsistency is simply illogical.

In fact, it seems to me you increase the risk of getting in the water with your tank turned off if you do this (especially if you don't purge it).

That argument could be made, I guess. But, getting in the water with your cylinder valve closed really has nothing to do with the issue of closing the valve, or leaving it open, after assembly. Rather, it has to do with a poor / incomplete pre-dive check. I check my gear immediately before entering the water, whether I have assembled it 10 minutes before, or two hours before. The assembly procedure and the pre-dive (safety) procedure are two entirely different activities, and should be treated as such.

I have been told that I could damage my regulator if it is left pressurized in the sun -- compelling, if true!

And, there are no objective data (and therefore no compelling reason) to support such a belief.

I have also heard instructors use the argument that it is better to find out that you have a slow leak before entering the water, therefore it is better to leave the valve open. I understand the logic but don't subscribe to it. I would rather start with a full cylinder, monitor my pressure after splashing, and then end the dive early if I find my pressure is dropping more rapidly than expected, than a) either start with a half-empty cylinder, or b) not splash at all.

What are your views?

I assemble the scuba unit, pressurize the system, check my cylinder pressure, check the function of my second stages and the inflator, then close the cylinder valve and purge the system. When I get ready to enter the water, AND I have donned my scuba unit (after opening the cylinder valve), I go through a pre-dive safety check in which I (again) check the cylinder pressure, and function of the inflator and both second stages. For me, doing it this way consistently for each dive is the best approach.

 

[miketsp]

I do a half-way. After mounting I close the valve and blip/pulse the inflator to drop the manometer to just over 100bar.
This serves a multiple role. I always ensure at least some air in my BC, I test that the inflator isn't sticking and I leave enough air in the system to serve as a leak check on the way out. There is also no danger that I will look at my gauge, see it full and assume the valve is open.
I've been doing this routine for many years and it serves me fine.

 

[TMHeimer]

If I assemble everything and then drive to a site, I turn it off. Once I didn't and had to throw on the brakes which caused a free flow, for whatever reason. Once I'm at the site and gearing up the air stays on throughout both dives & surface interval (if not changing tanks of course.....). On a boat (which I rarely do) I am just super carefull air is on before I jump in, as this is where the real danger is, as pointed out. I have entered shore dives 3-4 times over the years with air turned off--that's just inconvenient & perhaps embarrasing (unless of course you swim just 5 feet out and it's already 50 feet deep).

 

[spectrum]

In my experieince the single biggest risk in diving is a disruption to your routine. That being said for most folks it's air on, test and dive. Turning it off for an interval does intoduce a risk that you will forget to reopen the valve and the recovery from that can be an issue, maybe a big one.

I would not give any creedence to equipment being damaged by standing by under pressure. However if the gear is getting hauled in a heap you never know when a din connection will get wrenched or a purge depressed and that could cost you a dive. If a rig tumbles and there is damage you could have a live hose whipping. A sheared valve will ruin the day regardless.

I have one buddy that uses the interval as a pressure test. By airing up, testing then shutting doewn he is able to make a pre-dive pressure hold confirmation. As such it is his habit to air up immediately before donning.

I think the big take away is to be consistent.

Pete

 

[FinnMom]

I shut the air off but don't purge. I would never skip on the pre-dive check and I always do several things that all all require air: reg1 3 breaths, reg2 3 breaths, air goes into suit?, air comes out of suit?, air into wing?, air out of wing?, manual inflate of wing. <= I like this last one because it also keeps it well in mind that manual inflation is an option. You might even remember that under extreme stress. The air in/out of suit check is also very unlikely to ever let me jump in with a suit zipper open. I inflate until I can feel that the suit is indeed inflating; if it's leaking any great amount I think I should be able to feel it.

And finally, even with a single tank I can turn on my own air. I'm also in less trouble because I manually inflated the wing. I can leisurely turn on my own air if I'm at the surface. The wing being inflated also means that even if I slip, fall in and hit my head, I'm not gonna sink. Even if my air is off, I'm not gonna sink.

Some things are absolute. I raised 3 kids while living between a busy road and deep river. When they were too young to be strong swimmers we never, ever let them be outside and out of our sight. It's not hard, it's very simple: you just do it. The checks are like that too.

 

[DevonDiver]

I understand why some people use 'pressurized, but off' as a pre-test for leaks etc. However, the correct time to test the integrity and function of your kit is at home before going diving, not on the dive boat.

Turning off and de-pressurizing is a fool-proof way to absolutely ensure you cannot encounter a human error and enter the water with your air off (a potentially fatal consequence). If you have a protocol that works effectively to eliminate a potential risk, then it's illogical not to use it.

For those that feel they are beyond making a human error, and thus that risk does not apply to them, you still have something to learn. Why wait for the reality check to bite you in the ass?

 

[spectrum]

I understand why some people use 'pressurized, but off' as a pre-test for leaks etc. However, the correct time to test the integrity and function of your kit is at home before going diving, not on the dive boat.?

I know what you are saying but if you are diving regulary then your last dive is good as any at home test. Furthermore the only set-up that matters is the one you are taking into the water that time.

 

[Islandheart]

So on the dive boat two weeks ago, as we're up and moving towards the dive platform to begin our dive, the young fellow
in front of me turns and says, "Hey, turn my air please".

As I turn his air on I ask, "why is it off ?...

He replys, "I always turn it off, after I turn it on... and we've been diving so long, we don't need to do Pre-Dive safety checks anymore"...

I just smiled at him, shook my head and said, "Oh Really" ???