Question regarding tank fills

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Tracy

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There is a lot to be said for a Faber steel LP 95. Low fill pressure ( 2400 + 10%). At 2640 psi the tank holds a little over 100cf. I like the negative weight too. The down side is that the tank is a little wider and increases drag slightly.
The other cats meow is a set of old Scubapro steel 72's doubled. Again, these low pressure tanks can be pumped up 10% and provide a little over 150 cubic feet. I like them doubled because they are only 7 1/2 inches in circumference each and have a very low drag profile.
Don't skip the deco stops...........
I'm not sure where your information comes from, but stated volume is calculated at fill pressure.
A 95 is 95 cf at 2640, not at 2400.
Same with a steel 72, they are 72cf at 2475, not 2250.
 

AfterDark

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Hi, all, as the title suggests, I have a question regarding the tank fills at my LDS. I have a steel 100 tank that I use all but exclusively.

As far as I understand, the shop does a sort of quick fill method; they overpressurize the tank, and then cool the tank in water so that, when cool, it should be at the rated pressure of the tank, either 3000 for their 80s, or 3442 for my 100.

I've never had it filled to 3442 psi; I think the closest I ever came was 3000. I had a yearly visual done on the tank a few weeks ago, and when the tank was filled afterward, my SPG showed a pressure of 2500. I felt a little ripped off, but I didn't mention it to the LDS because it had been a couple of weeks since the fill that I went diving, and I'm not really sure I understand enough about the fill process to make an educated complaint.

This afternoon, I got another fill at the LDS for a dive planned for tomorrow. I just put the SPG on the tank, and it's showing a pressure of 2200. Am I right in thinking that something's wrong in this situation? I get it that pressure drops as the air cools, but it shouldn't drop that much, right? Am I missing something?

(I do plan on asking them if I can use one of their full tanks to check and make sure that it's not my SPG, but I thought I'd start here in the meantime)

I finally was able to do what I've always wanted to do and buy a compressor WK 4.2 @ 4000psi.
It is glorious! No short fills, not anymore now they are all 10% over! +stamp? What +stamp I don't need no stinking +stamp! It is wonderful to know when I start my dive I have as much air as I can carry. And if I make a quick dive and use only 1000psi just top it off at 10% over. Sometimes I use my pony to repair my daughter's pools. Same deal. I have a VIP light; do my own VIPs. If it's clean, no rust good, if I see rust off to the LDS they can evaluate, remedy and certify. With 9 tanks that's $22.00 a VIP, yearly, not anymore, mostly.

I fill my tanks in a barrel of 45 degree well water often they are cooler after the fill than before and never are less than the pressure I filled them to, there is no post fill cool off needed.
 

Charles2

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I invite you to show me pictures of a steel tank that has blown up while within hydro. Now look for the same in aluminum.

This does not answer my question. Neither does your video. I am pretty sure that shooting high caliber ammunition at scuba tanks does not certify tank integrity.

Steel and aluminum are different materials with different properties.

We have already agreed with this statement.

One of the differences is steels ability to stretch and then return to shape

If you believe this to be the main difference between steel and aluminum, you must be petrified with fear when flying on an airplane and watching the aluminum wings flex during turbulence.

Again, the design criteria for 3AA tanks and 3AL tanks appear to take into consideration the property differences between aluminum and steel. One should exercise the same amount of caution when overfilling either.
 

BRT

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This does not answer my question. Neither does your video. I am pretty sure that shooting high caliber ammunition at scuba tanks does not certify tank integrity.



We have already agreed with this statement.



If you believe this to be the main difference between steel and aluminum, you must be petrified with fear when flying on an airplane and watching the aluminum wings flex during turbulence.

Again, the design criteria for 3AA tanks and 3AL tanks appear to take into consideration the property differences between aluminum and steel. One should exercise the same amount of caution when overfilling either.
I am not petrified while flying because they take them out of service and crack check them after so many cycles. Because they are made out of aluminum. If you can't see in the shooting video that steel holds up better than aluminum I certainly can't help you. Sorry.
 

Rol diy

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If you believe this to be the main difference between steel and aluminum, you must be petrified with fear when flying on an airplane and watching the aluminum wings flex during turbulence.

Oh???? That's why they don't use some air frames after a certain amount of hrs? Aluminum fatigues after stretching.... look at aluminum fenders on trailers that vibrate. They stress crack like crazy... steel fenders are not nearly as bad.
If an aluminum tank does stretch it doesn't fatigue....
 

Charles2

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I am not petrified while flying because they take them out of service and crack check them after so many cycles. Because they are made out of aluminum. If you can't see in the shooting video that steel holds up better than aluminum I certainly can't help you. Sorry.

Oh???? That's why they don't use some air frames after a certain amount of hrs? Aluminum fatigues after stretching.... look at aluminum fenders on trailers that vibrate. They stress crack like crazy... steel fenders are not nearly as bad.
If an aluminum tank does stretch it doesn't fatigue....

Anecdotal evidence does not convince anyone of the validity of your arguments.
 

BRT

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Anecdotal evidence does not convince anyone of the validity of your arguments.
Don't know why I'm bothering...
Boeing 737 cracks: how common are they, and should you be worried?
Understanding the New Widespread Fatigue Damage Rule
Boeing Says It Didn’t Expect Cracks in 737s So Soon (Published 2011)

Essentially an AL80 and an HP100 are very similar in size and weight. The steel HP100 has much thinner walls and can take much higher pressures and you will not find pictures of a blown up steel tank unless it was deliberately pumped to an extreme pressure or was rusted badly.
 

scubadada

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I was recently on a liveaboard that offered AL80s and AL100s, they were both filled to the same pressure, an average of 3084 psi. I dived an AL80 and had an average fill of 79.6 cu ft. Divers with the AL100s has an average fill of 93.4 cu ft, not quite the differential they were expecting. The larger cylinders cost $10/day.
 

AfterDark

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I was recently on a liveaboard that offered AL80s and AL100s, they were both filled to the same pressure. average of 3084 psi, I dived an AL80 and had average fill of
Keeping us in suspense?
 
https://www.shearwater.com/products/swift/

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