Consensus on Overfilling Tanks?

[rob.mwpropane]

it's not THAT much of the wild wild west down there

Tbh, I don't think it is. I think it's perceived that way because of people's ignorance. Any practice outside of what would be considered "normal" would be viewed that way though.

 

[rob.mwpropane]

I can’t dig it up now. In an earlier thread on over fills LP tanks etc. I list it in detail. Searching for that should find it and give you more discussion. Quoting here would help others if you find it.

Cave fills?

This one?

 

[MichaelMc]

Cave fills?

This one?

No earlier. I cite and quote sections from the spec. Chapter and verse as it were.

 

[MichaelMc]

This:

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.

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.

Extracting:
"""
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.

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.

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.
"""

Rereading this I'm not sure about it being above service if at 70F. But it can clearly be above that if warmer.

 

[martincohn]

If you ordered well done (ewwww) and it came out rare you would sent it back.

Why shouldn't your tank fill be any different. If its a short fill ask them to top it off.

 

[tbone1004]

@MichaelMc is the "except plus rated" meaning it's at their stamped service pressure? I.e. 2400*5/4?

Either way, I imagine that the gas in the tanks is over 130f in most fill stations...

 

[abnfrog]

first of all there is no reason if you pay for a full tank you don't get one .....second I would like to see here someone quoting safe practices etc show their current fill station operator card to prove such .......third what tbone said ,show the documentation ....im really tired of people spouting about their experience in their shop when they don't have or never did own a "SHOP" their garage where they store gear is not a scuba shop or reselling what they buy online from DGX. get in the business and buy a compressor or don't pretend to have one ...... and qualifications

 

[MichaelMc]

@MichaelMc is the "except plus rated" meaning it's at their stamped service pressure? I.e. 2400*5/4?

Either way, I imagine that the gas in the tanks is over 130f in most fill stations...

"§ 173.301a
(c) Cylinder pressure at 21 °C (70 °F). The pressure in a cylinder at 21 °C (70 °F) may not exceed the service pressure for which the cylinder is marked or designated, except as provided in § 173.302a(b). ...

(d) Cylinder pressure at 55 °C (131 °F). The pressure in a cylinder at 55 °C (131 °F) may not exceed 5/4 times the service pressure, except:
(2) For a cylinder filled in accordance with § 173.302a(b), the pressure in the cylinder at 55 °C (131 °F) may not exceed 5/4 times the filling pressure.
...
"

When I read it they did not seem to talk about what happens at other temperatures AND the two temps they lay out are not on the same gas expansion curve, so the only way to hit both is to hit the lower one. It's not clear what they achieved by having their high temp point above the curve. Other than recognizing that pressure can be higher at higher temps.

To be clear, my earlier comments about hitting either point seem wrong. If you are at 70F it reads that you need to be below the service pressure. I added strike out to the hitting either constraint in my earlier post.

I am not a trained well informed fill operator. I just read the spec. It provides for higher pressure at higher temps.

 

[tbone1004]

@abnfrog I learned running a government owned compressor at a university that had to comply with all of the nonsense that is associated with that... VERY different experience than operating shop pumps

@MichaelMc haven't run the math, but it's probably just an "easy" ratio for them to call out

 

[abnfrog]

yep t bone your right but we are talking scuba industry here and I know you know what you are talking about but the "others " are self professed experts .....and its starting to get to me