Don't breathe tanks to zero?

[Paulmal]

Letting someone else analyze your mix just breeds complacency IMO. Was the gas free or something? Fairly pointless to use nitrox in a pool and 60' is really marginal for any value at all.

I find breathing nitrox at depths of 60 ft and less really speeds up my deco stops.

Depending on where you dive the difference between nitrox and air fill cost is only a couple of bucks, if nothing else it's good for added safety.

 

[Peter69_56]

As long as there is pressure in the tank, nothing will enter that tank except through a fill whip. So shops usually check pressure before a fill so they7 know the only thing in that tank is what they or some other fill op has added. Of course, that does not keep a fill op from screwing up and getting water in your tank but tehy seem to gain some comfort (or charge for another VIS) by thinking they know the user did not screw it up.

Now, is it really so bad to drain YOUR tank. Not if you exercise just a little care not to let anything harmful enter. And ambient air that would enter through an open valve or a removed valve is not harmful unless you also allow something else in. But the stories are interesting.

I like to inspect my own tanks periodically - before a VIP and after any suspect fill.

Be good or Santa will leave you nothing but coal.

Often salt water gets in because the filling attendant doesn't blow the valve mouth clear before attaching the whip to a cylinder fresh from salt water. Each time this is done, a little salt water gets blown in. I believe this is the main cause of salt ingress into cylinders and not just low cylinder pressure. The salt gets into the valve opening often from salt spray on cylinders with no regulator on them etc when travelling back from the dive site or cylinders washed when back in the dive shop before refilling (we do wash our cylinders on return ? Don't we?)

---------- Post added July 6th, 2013 at 05:19 PM ----------

Do people actually do that?

Simply put, yes, particularly Pacific dive sites that do PP fills, and in particular when asking for say 50-60% Nx. Makes doing gas usage calcs even more important. Do I dump the cylinder or do I have enough deco gas for one more dive?

 

[eelnoraa]

I have a couple of overbalanced first stages that actually breathe much easier on the last breath before they shut off mid breath.

Not sure if this is what you have, but over balance (Apkes, Oceanic/Hollis) actually refers to IP increase with respect to depth, not tank pressure.

 

[AfterDark]

I find breathing nitrox at depths of 60 ft and less really speeds up my deco stops.

Depending on where you dive the difference between nitrox and air fill cost is only a couple of bucks, if nothing else it's good for added safety.

A couple of bucks? I must dive in hell, here in hell a Nitrox fill is double what an air fill costs. I almost never use Nitrox. I got it mostly for trips like to NC where I just did 7 dives but only 2 on Nitrox. The weather was so bad we didn't know until after we left the dock it we'd be diving 60fsw or 130fsw.

I did breathe a tank down once. I was entangled but very close to the surface, 2-3 feet. It was a job so I was alone. After I sucked every air moulcule out of the tank trying to get free, I ditched the tank (no BC) and surfaced which of course is what I should have done in the 1st place, stubborn. The next VIP found rust on the bottom of the tank which was rolled. Cause? It was blamed on that incident.

 

[The Chairman]

Filling partially empty tanks is a cinch with any number of mobile phone apps for the task. Here's one for the Android: https://play.google.com/store/apps/details?id=divestoclimb.scuba.equipment&hl=en

 

[billt4sf]

Gosh. 10 pages on whether it is OK for the TANK to breathe it down to zero. More hot air here than in the tank! lol

 

[Abdullah]

Filling partially empty tanks is a cinch with any number of mobile phone apps for the task. Here's one for the Android: https://play.google.com/store/apps/details?id=divestoclimb.scuba.equipment&hl=en

You are correct on the apps, they make the math a snap (dare I say idiot proof). I also have nice desk top calculator. But, you have to know both residual mix and the residual pressure accurately. Measuring those for a single tank isn't much of a bother. Measuring those on a couple dozen tanks is a real PITA. OTOH, if I crack the valves on all those tanks I can go do something else while they blow down, then come back and do all the fills.

 

[Jon_R]

Letting someone else analyze your mix just breeds complacency IMO. Was the gas free or something? Fairly pointless to use nitrox in a pool and 60' is really marginal for any value at all.

Nitrox fills are 7 bucks air fills are 4 bucks. If you have a nitrox tank I didn't think you where supposed to get regular air fills in the tank. In that case I would be getting ean 21 for 7 bucks so just went with ean 36. Was my first fill after getting the tank and first time breathing enhanced air so just got the 36 in case something goofy happened breathing it I would just be in my pool.

I am only padi OW so not supposed to go below 60 right now. Only got OW in may so definite newbie and learning.


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[chrpai]

Nitrox fills are 7 bucks air fills are 4 bucks. If you have a nitrox tank I didn't think you where supposed to get regular air fills in the tank. In that case I would be getting ean 21 for 7 bucks so just went with ean 36. Was my first fill after getting the tank and first time breathing enhanced air so just got the 36 in case something goofy happened breathing it I would just be in my pool.

It depends. If the nitrox tank is O2 clean then no, you don't get "regular" air fills. Regular (aka grade E ) air fills will contaminate the tank. But if the LDS makes nitrox then it's a given that they don't pump grade E air. Their air is O2 compatible and therefore won't contaminate the tank.

At that point you get into the stupid "NITROX ONLY" stickers. Pointless bumper stickers don't belong on tanks. The tank contents marking is what matters. But yes, you can put EAN 21 in the tank and mark it as such and I would expect to pay $4 not $7 for that fill.

Someone can (and will no doubt) argue that you are getting the benefit of 36% on a 30' training dive but I would claim nonsense.

 

[Jon_R]

It depends. If the nitrox tank is O2 clean then no, you don't get "regular" air fills. Regular (aka grade E ) air fills will contaminate the tank. But if the LDS makes nitrox then it's a given that they don't pump grade E air. Their air is O2 compatible and therefore won't contaminate the tank.

At that point you get into the stupid "NITROX ONLY" stickers. Pointless bumper stickers don't belong on tanks. The tank contents marking is what matters. But yes, you can put EAN 21 in the tank and mark it as such and I would expect to pay $4 not $7 for that fill.

Someone can (and will no doubt) argue that you are getting the benefit of 36% on a 30' training dive but I would claim nonsense.

The tank is o2 cleaned I took it down to 200psi yesterday so I could check my weighting with an empty tank. No weight and still sink like a rock so should not need much in ocean. 4-6 lbs should be plenty.

When I get it filled I will ask the shop my options on fills. Thanks for the info.

My daughter has 2 al 63s. Probably get those scrubbed at some point so good to know the options. Then I have girlfriend and son in OW class....


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