AL80 Fill amount??

[kstakem]

Hi all,

I was wondering what the normal fill amount in PSI would be for an AL 80? I am assuming 3000psi based off what I have heard.

The reason I ask is I just got a tank filled and when I got home and hooked up my dive computer to it, it only read at 2765. All my gear is new, and I haven't checked the calibration of my dive computers PSI values. Its a Cobra if that matters. I wonder what the odds of the computer values being off are?

I understand that there are other factors in a tank fill like air temp, etc.. but doesnt that get taken into consideration when the tank is filled?

Thanks

Kevin

 

[jonnythan]

When air is compressed into a chamber (tank), gas gets significantly warmer. The warmer the gas, the more pressure is exerted for a given volume. So if you fill a tank in 10 minutes to 3000 psi, when it cools it might get down to 2700 psi or so. Some shops immerse the tanks in cool water while filling (which I hear doesn't do much). Many dive shops do an initial fill, then wait a while and top it off again so it reads closer to 3000 when you take it home.

Then again, I imagine many dive shops don't. Typical fills on my tanks are between 2800 and 3100 psi cold.. So 2765 isn't all that unusual, but you might want to talk to the dive shop about it.

 

[raxafarian]

probably temperature..

got my lp95's filled last night... the shop was busy filling tanks for a trip, but squeezed mine in. He asked if I could wait for them to cool, so he could top 'em off... I said no...just fill 'em to 2800psi.. checked them this morning, and they are 2400... which is fine for the diving I have planned.

If you walk in for a fill, you could have this trouble... if you talk to them, and drop off your tanks a day before, they should be able to fill 'em to 3000.



Disclaimer: do NOT fill your tanks above rated pressure... ESPECIALLY aluminum tanks.

 

[kstakem]

I figured it was cause he filled it fast and the warmer air caused the pressure drop when it cooled, but just wanted to make sure. I am a new diver and need all the air I can get

I was kinda surprised when he brought it back like 5 minutes later and said it was all done.

Thanks for the info

Kevin

 

[Spectre]

kstakem once bubbled...
I was wondering what the normal fill amount in PSI would be for an AL 80? I am assuming 3000psi based off what I have heard.

I would sit down with your instructor or your LDS and have them explain to you how the tank markings work. In those 'numbers' on the neck of the tank, the working pressure is stamped.

As far as the short fill... yes, he probably filled it too quick and the 'real' amount of air in the tank showed when it cooled.

 

[scubafanatic]

That's pretty much what I've experienced......and most shops/dive locations are too busy or lazy to bother with the "I'll leave it a while and top it off later" routine.

I use LP 120's steels.......and since steel tanks are over-engineered and somewhat elastic.....they are much more tolerant of overfilling........so for example, if I go to 3300 psi 'hot', they typically cool down to somewhere between 2900 and 3000 psi by dive time......which gives me 132 to 136 cu. ft..

The typical 3000 psi AL80 'hot' fill usually drops to about 2700 psi by dive time.....and since the AL80 is really only a 77.4 cu ft. tank @ 3000 psi......a 2700 psi 'cold' fill = 70 cu. ft of air.

Unfortunately, aluminum is a brittle metal and CANNOT be 'stretched' ......so I recommend against any 'overfilling' as aluminum can't take the stress.

I've never owned aluminum tanks, so maybe others on the board can address whether or not aluminum can safely be overfilled briefly until the tank cools down to 3000 psi......I've heard it's unsafe.

Karl

 

[O-ring]

Kevin,
If you want we can hook up one of my regs with an analog SPG on it next time we are out at the quarry and just make sure the numbers jibe.

We usually get 3100-3300 fills in AL80s..

 

[donacheson]

scubafanatic once bubbled...


Unfortunately, aluminum is a brittle metal and CANNOT be 'stretched' ......so I recommend against any 'overfilling' as aluminum can't take the stress.

Karl

In two words: That's nonsense.

 

[WreckWriter]

My average fill is about 3300. I've gotten 3500 a couple times but feel comfortable with 33-3400.

Tom

 

[kstakem]

Thanks everyone for the posts.

Hey O-Ring, i would like to hook up your SPG and check it against my Dive computer just for hell of it next time we are together.

Kevin