tank size and pressure
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MichaelMc
Working toward Cenotes
So, when your displayed pages say 'Fill ... to marked service pressure',
The US regulation's specified service pressure for a + rated 3AA cylinder is 10% more than the pressure stamped on the cylinder. So is 'stamped' (on the cylinder) different from 'marked' as used in the pages you show? Or do these pages not account for a by regulation handling of + rated cylinders? Or 'account' for them in a 'safer by a bit' margin for simplicity.
Is this Reminders page perhaps a simplification, leaving out some of the more gritty details? Or does the body of this PSI manual not track the regulations?
The US regulation's specified service pressure for a + rated 3AA cylinder is 10% more than the pressure stamped on the cylinder. So is 'stamped' (on the cylinder) different from 'marked' as used in the pages you show? Or do these pages not account for a by regulation handling of + rated cylinders? Or 'account' for them in a 'safer by a bit' margin for simplicity.
Is this Reminders page perhaps a simplification, leaving out some of the more gritty details? Or does the body of this PSI manual not track the regulations?
W W Meixner
Banned
Michael...
I'll go through the complete training manual tonight and reply in the morning...I highly doubt the manual is going to contradict itself...and + 10% is the manufacturers stamp...so an additional 10% would be acceptable...and in my opinion...not considered ''over-filling''...
W...
Bob DBF
Contributor
I would agree, however the service pressure never changes, even though the allowable fill pressure does when the plus is stamped at hydro. A matter of precision when the book was being written. Kind of like a number of my posts, I know what I'm saying, but the sentence I write leaves room for misinterpretation.
Bob
PS Assuming I know what I'm talking about in the first place.
You are using the PSI book and that is fine ....Now get on the phone and call psi and see just what that (go not overfill) statement means. on a al80 tank that is marked 3000 psi. the psi is not absolute. It is a measurement at a GIVEN TEMERATURE. If you have a tank at 3000 and the tank is 50F it is over filled.I know you know this because you used that logic process in your prior post. The standard is 3000 at 70F. You are unable to measure the tank internals so some shops say (SHOP POLICY) to cool and top off. It is that same lame (SHOP POLICY ) THAT SAYS NO TANKS OLDER THAN 20 YEARS can be filled. It comes from not trusting the fillers to check the tanks so they make global policies. If you fill a tank like you say you did and it was in a 70F shop. and the customer gets that tank and takes it outside to the lake and it heats up to 90F Is the tank over filled because the temp raised the psi up 100 psi? Is the customer required to vent the tank because it is over pressured? The answer is no to both cases Because the tank would have 3000 on the noodle doodle if at 70F. Lastly regarding PSI they will tell you that their program is not DESIGNED AS a safety program. It is a program that if followed will prevent you from loosing a law suit if one if filed against you. The byproduct is that you will have complied with all the safety regs in existance to be suit free.
MichaelMc
Working toward Cenotes
Yes, and I miss-spoke when I wrote the service pressure changed for plus rated cylinders.
For 3AA cylinders, 49 CFR 173.302a para (b) describes:
may be 'filled ... 10 percent in excess of its marked service pressure, provided:"
49 CFR § 173.302a - Additional requirements for shipment of nonliquefied (permanent) compressed gases in specification cylinders.
I am curious if the body of the PSI manual agreed that.
On filling a warm cylinder, the CFR describes two temp/pressure pairs. One at 70F, one at 131F.
49 CFR 173.301a para (c) and (d):
(c) “at 21 °C (70 °F) may not exceed service pressure” except [plus rated]
(d) “at 55 °C (131 °F) may not exceed 5/4 times the service pressure” except [plus rated]
49 CFR § 173.301a - Additional general requirements for shipment of specification cylinders.
I do not know why this 5/4 allowance seems to be twice what P/T would account for adding to a warm tank. But by these regs there is nothing against a warm tank being at higher pressure, provided if the cylinder is at either of the specified temps it is under their respective pressures. And the higher temp pressure is generous relative to the 70F one for scuba pressures and P/T. This seems to leave good room for a warm fill to cool to an at spec 70F fill.
Do PSI or TDI treat service pressure independent of temp or do they note that there is a higher bound for warm cylinders? And that this may well influence a, by reg pressure limits, filling procedure. I am told by one source that neither PSI nor TDI manuals address temp during filling. Which seems a lack given the regs clear two temp standard.
ETA: fix some misstypes of 131/130/etc.
For 3AA cylinders, 49 CFR 173.302a para (b) describes:
may be 'filled ... 10 percent in excess of its marked service pressure, provided:"
49 CFR § 173.302a - Additional requirements for shipment of nonliquefied (permanent) compressed gases in specification cylinders.
I am curious if the body of the PSI manual agreed that.
On filling a warm cylinder, the CFR describes two temp/pressure pairs. One at 70F, one at 131F.
49 CFR 173.301a para (c) and (d):
(c) “at 21 °C (70 °F) may not exceed service pressure” except [plus rated]
(d) “at 55 °C (131 °F) may not exceed 5/4 times the service pressure” except [plus rated]
49 CFR § 173.301a - Additional general requirements for shipment of specification cylinders.
I do not know why this 5/4 allowance seems to be twice what P/T would account for adding to a warm tank. But by these regs there is nothing against a warm tank being at higher pressure, provided if the cylinder is at either of the specified temps it is under their respective pressures. And the higher temp pressure is generous relative to the 70F one for scuba pressures and P/T. This seems to leave good room for a warm fill to cool to an at spec 70F fill.
Do PSI or TDI treat service pressure independent of temp or do they note that there is a higher bound for warm cylinders? And that this may well influence a, by reg pressure limits, filling procedure. I am told by one source that neither PSI nor TDI manuals address temp during filling. Which seems a lack given the regs clear two temp standard.
ETA: fix some misstypes of 131/130/etc.
W W Meixner
Banned
MichaelMc
Working toward Cenotes
The 49 CFR 173.302a para (b) plus pressure is described by 49 CFR 173.301a para (c) and (d) as the 'filling' pressure for the + rated cylinders. Given the use of 'filling' that may seem a complication in deciding what you should 'fill' the tank to. Yet it seems clear that it is a 70F 'filling' pressure, and the spec explicitly states that the 131F 5/4 rule applies to this plus rated 'filling' pressure. So, it seems clear, 'filling' should be read as '70F filling'.
And of course, a safe pressure procedure would certainly be fill any tank, rated over 1000, to no more than 1000 psi. Whether that is warranted, ..., it clearly has no basis for necessity in the regs. Nor would several other overly aggressive simplifications.
My P/T calcs showed that 3015 psia at 70F warmed to 131F becomes 3364 psia, that would cool to the 70F spec. While the 5/4 rule for 131F allows it to be a rather high 3750 psi. Lots of by spec headroom above what is needed to let a warm fill cool to a spec'ed 70F fill.
And of course, a safe pressure procedure would certainly be fill any tank, rated over 1000, to no more than 1000 psi. Whether that is warranted, ..., it clearly has no basis for necessity in the regs. Nor would several other overly aggressive simplifications.
My P/T calcs showed that 3015 psia at 70F warmed to 131F becomes 3364 psia, that would cool to the 70F spec. While the 5/4 rule for 131F allows it to be a rather high 3750 psi. Lots of by spec headroom above what is needed to let a warm fill cool to a spec'ed 70F fill.
2airishuman
Contributor
I'm amazed that people will recommend overfilling LP steels to recreational divers who are asking general questions about cylinders.
There are so many reasons why it's a bad thing to recommend.
There are so many reasons why it's a bad thing to recommend.
- As a practical matter, overfills are simply not available to most recreational divers. Dive shops outside cave country don't offer them.
- HP steels have been in production since 1987 and are readily available new or used. People who want HP fills can get HP cylinders.
- Burst disc failures can cause injury or property damage. Many if not most divers getting "cave fills" use an over-spec burst disc or blanking plug. Rec divers who don't realize that a burst disc change is part of the package are at greater risk from a failure. I believe @CuzzA had this happen. On the other hand, over-specing or blanking out a burst disc poses its own risks.
- While there are not believed to have been any cylinder ruptures caused by cave fills, that doesn't mean the practice is safe enough for general recreational diving. a) There simply haven't been enough cave fills performed to draw a conclusion, especially to the higher pressures now considered acceptable. b) The field experience with cave fills is limited to those cylinders typically used for cave diving and should not be generalized to other types of LP steels, especially older, smaller cylinders such as LP72s and some LP50/LP52s.
- While the jurisdictional questions are complex and enforcement spotty, it is unlawful under some circumstances.
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