Tank overfill

[Kestrell]

Okay, I just got my tank filled and my wife's tank too, a few days ago.

As an aside,to my knowlewdge, my wife has yet to pay for anything related to diving. I'm not sure how she does this.

Anyway, the guy filling the tanks hands me my tank and says, I filled it to 3800 so when it cools down you should be right around 3400-3500. That's cool. I have a PST E8 130 so I have a complete fill.

Well when he gave me my wife's tank he said something similar, but I didn't really hear what he said. I assumed he put in a bit of an overfill so when the tank cools it will be at max pressure.

Max pressure for my wife's tank is 2400 since she has a Faber LP 85.

Well, afew days later, just for the fun of it, I decided to see how close the guy got to filling the tanks to their max.

I checked mine and the pressure gauge was reading just bekow 3500. Great.

When I checked my wife's tank it the needle was right on 3000. By my calculations that is a 25% overfill.

Is this going to damage her tank? Its been at that pressure for a few days now. Is it even safe? If so, how long can it stay like that?

 

[DepthCharge]

Okay, I just got my tank filled and my wife's tank too, a few days ago.

As an aside,to my knowlewdge, my wife has yet to pay for anything related to diving. I'm not sure how she does this.

Anyway, the guy filling the tanks hands me my tank and says, I filled it to 3800 so when it cools down you should be right around 3400-3500. That's cool. I have a PST E8 130 so I have a complete fill.

Well when he gave me my wife's tank he said something similar, but I didn't really hear what he said. I assumed he put in a bit of an overfill so when the tank cools it will be at max pressure.

Max pressure for my wife's tank is 2400 since she has a Faber LP 85.

Well, afew days later, just for the fun of it, I decided to see how close the guy got to filling the tanks to their max.

I checked mine and the pressure gauge was reading just bekow 3500. Great.

When I checked my wife's tank it the needle was right on 3000. By my calculations that is a 25% overfill.

Is this going to damage her tank? Its been at that pressure for a few days now. Is it even safe? If so, how long can it stay like that?

I routinely fill my steel LP tanks to 3500-4000 psi. Still pass the hydro with "+" rating. I wouldn't overfill aluminum tanks tho............they can't take the pressures. Faber claims life of their steel LP tanks to be something like 10,000 cycles @ 4,000 psi. So it seems it'll last for me

 

[jonnythan]

Faber claims life of their steel LP tanks to be something like 10,000 cycles @ 4,000 psi. So it seems it'll last for me

Where do they claim that?

 

[padiscubapro]

Where do they claim that?

Its used to be in their technical documents, not sure if its still there.. Even OMS who used to be a major distributor for OMS tanks (rebranded) used to have (until they switched to hp tanks) this info prominately posted on their web sites..

 

[lamont]

Where do they claim that?

i believe that's from DOT standards. the DOT-E9791 standards which the E-series uses states this:

``Cycle Test .Three cylinders must be cycle tested to destruction to an upper cyclic pressure of 1.5 times service pressure.The successive hydrostatic pressurizations from the lower cyclic pressure to the upper cyclic pressure must not exceed a rate of ten cycles per minute.Adequate recording instrumentation must be provided if equipment is to be left unattended for any period of time.Lower cyclic pressure must not exceed 10 percent of the upper cyclic pressure.Cylinders must withstand at least 10,000 cyclic pressurizations without distortion or failure.The failure must occur in the sidewall and the failure mode must be leak before burst (LBB).At least one cylinder must be cycled using water as the pressurizing medium.''

the DOT-3AA regs are probably similar.

 

[Jim Baldwin]

Where do they claim that?

In several of the old Leisure Pro catalogs that I had I read the same thing 10,000 cycles at 4,000 psi. This was under the OMS tanks, bands, and valves section. This was for the LP 2400 series tanks.

My newest catalog is at least a year old but I don't remember seeing that statement in this version but I may have just missed it.

The low presssure PST 95 & 120's (2400) that I use in Cozumel routinuely show 2800-2900 and they get dove almost everyday. In Florida cave country this would be considered a good fill. I'm not advocating the overfill of tanks beyond their recommended pressure. I'm just telling you what I have found in experiences diving.

I dive PST HP 100 & 120's and it's rare when I can get a good 4000 fill. Once cool they are usually on 3500-3600.

 

[markfm]

I don't know squat about diving, but I am an engineer -- you are not supposed to go to the design point. We purposely overdesign, to take care of normal variance and wear and tear. 10% or so over nominal, fine, but please don't start pushing 50% above the rating, thinking that's a normal/okay thing to do.

It doesn't matter if a particular person has run with an overload for years -- this one is basic safety, in the same vein as why you don't stare at the SPG when you open the tank valve.

The "service pressure" is precisely that -- the normal pressure the tank should be operated at.

 

[mike_s]

I've heard that it's pretty routine to fill LP tanks (2400psi) to 3000psi or 3300psi, or maybe even 3500psi..... now 3350 is about 40% overfill. I see this a lot. I've hard that the burst psi was 10,000psi also.

so I know it doesn't make it right, but it seems that this is done often.

 

[markfm]

It's a case of just not a smart thing to do. I could probably pump my car tires up to 60 psi, just not a swift move on my part.

When you get your 5 year hydro test, it's at 5/3 -- in other words a 2400 tank gets tested to 2400x5/3 = 4000 psi. Do you really want to be doing an air fill that's anywhere near the test pressure purposely designed to check for incipient failure? Of course, the hydro test is done with water, so it's less compressible/expandable; when a hydro'd tank goes "boom" it's not as impressive as when an air-fill goes bad.

The idea is that during the 5 years between hydros there is normal wear and tear -- things get banged up a bit, stressed a bit... You then test by going significantly beyond the normal working pressure to see if all is well. If you want to drive your tanks at 3300 as the norm, they should be getting hydro'd at 5500, and they should have the little magic DOT stamp showing they are rated 3300 working pressure, that the design of the tank, fab process, material used is all consistent with such a rating.

A 3K tank getting a 3300 fill is a don't-care, but a 2400 with 3500 is pushing the envelope, deliberately working outside the design of the system.

 

[Whitelightnin]

A 2400 tank filled to 3000 will be fine. That is normal for cave divers. They do fills like that every day. Don't worry about it.
James