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cow109
11-12-2007, 23:07
Let's say you carry a pony tank but never had occassion to use it (other than practice switching over), so you are basically storing it all the time with 3000 psi. Does that weaken it over time? If you go several months between dives should you bleed it to 300 psi during the downtime? Also, does air get stale and need to be changed more often than whenever the annual viz rolls around? (Enough dumb questions for one thread?) :smiley29:

texdiveguy
11-12-2007, 23:21
Let's say you carry a pony tank but never had occassion to use it (other than practice switching over), so you are basically storing it all the time with 3000 psi. Does that weaken it over time? If you go several months between dives should you bleed it to 300 psi during the downtime? Also, does air get stale and need to be changed more often than whenever the annual viz rolls around? (Enough dumb questions for one thread?) :smiley29:

Not a dumb question....you will get several different replies I warn you--lol.

Storing your Al. cylinder with 3000psi for several months prior to its next dive/skill work will not weaken or damage it.....if you are storing the cylinder for much longer periods of time, it is recommended to reduce the pressure still leaving some gas in to prevent moisture from entering the cylinder. The air will stay fine for long periods.....I would think though that during the course of a year you will breath down the cylinder pressure enough during practice and occasional test usage to have to top up with 'fresh' air at some point. The storage of gases be it air or nitrox (trimix having other issues of concern in addition to those of air/nitrox) in steel cylinders over periods of time is a bit more complex, but air in Al. cylinders is quite safe so long as you follow safe protocols and common sense.

BouzoukiJoe A.K.A. wrecker130 AKA Chuck Norris AKA joeforbroke (banned)
11-13-2007, 09:36
If you have an annual VIP no need to worry about storing it at high pressure.

texdiveguy
11-13-2007, 10:01
If you have an annual VIP no need to worry about storing it at pressure.

Many LDS in 'my area' will require the diver to have the cylinder re-inspected if the cylinder is brought in for a fill without some portion of an air charge still on it.....so if one was to bring the cylinder in for that mid year fill say...you might face another VIP prior to the LDS filling it. Just something to check on with your particular fill service. I persl. don't store cylinders without a gas charge of some degree remaining to prevent possible contamination.

RoadRacer1978
11-13-2007, 10:19
My LDS is the same way. If the tank is completely drained of all pressure you will have to get another VIP no matter how long since the last.

BouzoukiJoe A.K.A. wrecker130 AKA Chuck Norris AKA joeforbroke (banned)
11-13-2007, 11:21
If you have an annual VIP no need to worry about storing it at pressure.

Many LDS in 'my area' will require the diver to have the cylinder re-inspected if the cylinder is brought in for a fill without some portion of an air charge still on it.....so if one was to bring the cylinder in for that mid year fill say...you might face another VIP prior to the LDS filling it. Just something to check on with your particular fill service. I persl. don't store cylinders without a gas charge of some degree remaining to prevent possible contamination.

My post was ambiguous. What I meant was no problem storing it at high pressure. Of course you want to keep some pressure on it to avoid moisture contamination.

texdiveguy
11-13-2007, 11:25
[quote=BouzoukiJoe;91354]If you have an annual VIP no need to worry about storing it at pressure.


My post was ambiguous. What I meant was no problem storing it at high pressure. Of course you want to keep some pressure on it to avoid moisture contamination.

Ok...cool!! :-)

BouzoukiJoe A.K.A. wrecker130 AKA Chuck Norris AKA joeforbroke (banned)
11-13-2007, 11:28
My LDS is the same way. If the tank is completely drained of all pressure you will have to get another VIP no matter how long since the last.

I know of a place that officially makes you pay for a re-VIP of a rental tank that comes back with less than 750psi. In truth they don't enforce it until you get below 500 psi. I believe my LDS uses 300 psi as the re-VIP cut-off.

RoadRacer1978
11-13-2007, 11:35
Wow, having to pay a VIP on a rental. That is some crazy stuff.

quasimoto
11-13-2007, 15:41
Most will say that what weakens any tank is not the storage at pressure but rather the cycle of filling and draining. There are other factors but that is the most common cycle.

BouzoukiJoe A.K.A. wrecker130 AKA Chuck Norris AKA joeforbroke (banned)
11-13-2007, 15:47
Most will say that what weakens any tank is not the storage at pressure but rather the cycle of filling and draining. There are other factors but that is the most common cycle.

Yep. It's called metal fatigue. Aluminum is more subject to fatique while steel is more subject to rust. A properly maintained steel cylinder can last you 40 years. An aluminum tank might last 15.

No Misses
11-13-2007, 16:11
My LDS is the same way. If the tank is completely drained of all pressure you will have to get another VIP no matter how long since the last.

I know of a place that officially makes you pay for a re-VIP of a rental tank that comes back with less than 750psi. In truth they don't enforce it until you get below 500 psi. I believe my LDS uses 300 psi as the re-VIP cut-off.

Wow, 500 psi! I often drain my tanks down below 100 psi. One time I took in a tank with 40 psi. My OW instructor was doing the fills that day. He gave me a dirty look ;-)

As for going several months without filling the pony...On the last dive of most days, I switch to the pony at depth and breath it the whole way up. This does several things.
1. Re-enforce muscle memory.
2. Timed deployment under different conditions. I should be able to deploy the pony while not breathing from my primary. If for some reason I can not deploy it before I feel the need to breath, I am doing something wrong.
3. By deploying at depth I confirm that my reg is properly tuned and will work at any depth.
4. Fresh air in pony. It gets filled at least once per month.
5. Confirms that I can make a safe ascent from depth without running out of air. I don't have to stress about it. I have proven it several times, under different conditions.

BouzoukiJoe A.K.A. wrecker130 AKA Chuck Norris AKA joeforbroke (banned)
11-13-2007, 16:58
My LDS is the same way. If the tank is completely drained of all pressure you will have to get another VIP no matter how long since the last.

I know of a place that officially makes you pay for a re-VIP of a rental tank that comes back with less than 750psi. In truth they don't enforce it until you get below 500 psi. I believe my LDS uses 300 psi as the re-VIP cut-off.

Wow, 500 psi! I often drain my tanks down below 100 psi. One time I took in a tank with 40 psi. My OW instructor was doing the fills that day. He gave me a dirty look ;-)

As for going several months without filling the pony...On the last dive of most days, I switch to the pony at depth and breath it the whole way up. This does several things.
1. Re-enforce muscle memory.
2. Timed deployment under different conditions. I should be able to deploy the pony while not breathing from my primary. If for some reason I can not deploy it before I feel the need to breath, I am doing something wrong.
3. By deploying at depth I confirm that my reg is properly tuned and will work at any depth.
4. Fresh air in pony. It gets filled at least once per month.
5. Confirms that I can make a safe ascent from depth without running out of air. I don't have to stress about it. I have proven it several times, under different conditions.

Yep, I was amazed when I was asked to sign a form saying I'd pay for a VIP if I brought it back with less than 750 PSI. The owner of the shop told me the real cutoff was 500 psi. I would have gone somehwre else, but that would have taken another hour.

Your pony routine seems like a great idea. I think I might adopt it.