Warning about hot fills!

[divezonescuba]

Let'er rip.

An individual came by the other day that was extremely upset that we did not submerge our tanks in water while filling them. Some shops do, some shops don't. Around here most don't.

According to this individual, a tank hot filled to 3200 psi would cool down to 2100 psi if it was put in his garage for a week. He also stated that tanks that were hot filled would have a shorter service lifetime. He was so upset that he filed a Q and A on us with our certification agency.

Comments.

 

[Herb-alaska]

Let'er rip.

An individual came by the other day that was extremely upset that we did not submerge our tanks in water while filling them. Some shops do, some shops don't. Around here most don't.

According to this individual, a tank hot filled to 3200 psi would cool down to 2100 psi if it was put in his garage for a week. He also stated that tanks that were hot filled would have a shorter service lifetime. He was so upset that he filed a Q and A on us with our certification agency.

Comments.

I would think that if his hot filled tanks cool from 3200 down to 2100 in a week sitting in the garage that he has a leaking valve. We hot fill everything here and I have never seen anything cool and loose more that 200 -300 psi

I would not worry about the Q and A because if your certification agency knows anything they will know that he is full of it and discount his Q and A

I would have offered to let him come back in 2 hours after his tanks have cooled and I would top them off if necessary

 

[JohnN]

Perhaps he's living in a parallel universe where laws of physics do not apply. . .

Ideal Gas law: P*V/T = constant . . .

You'd have to see a ~50% change in ambient temperature to account for that much of a pressure differential. . .

 

[Wookie]

Filling in a water bath has far greater potential to introduce water into the cylinder than dry filling. <buzzer sound here>
Wet filling introduces a far greater temperature gradient across the cylinder wall, hot inside, colder outside, inducing stress across the cylinder wall. Does this shorten the life of the cylinder, probably not really, but just the opposite of your mis-informed client's impulse, wet filling would shorten the life of the cylinder <buzzer noise here>
Wet filling goes against everything PSI teaches. Not that PSI is the end all-be all of scuba cylinder handling, they are way smarter than me and are willing to do the research that I just don't have time for. <insert buzzer noise here>
Any douchebag who would file QA based on your fill procedures will sue you when he gets hurt because of his own stupidity. Fire the client immediately. It's such a good feeling to let a stressful situation go...

Next time, go to the gas house and watch them fill Oxygen bottles and tell the client how O2 are filled dry...

 

[Jim Lapenta]

Did you explain the 5 psi per degree factor to him? Bet he would not have heard anyway. Someone that files a Q & A over something like that you just shake your head and politely ask him to get his fills elsewhere. Glad I don't hot fill my LP tanks to 3100. Take em up to 2600 let em cool and then top em off so they are "cool filled" to 2800 - 3000. Unless heading to Erie. Then they may see 3100 - 3300.

 

[dfx]

Perhaps he's living in a parallel universe where laws of physics do not apply. . .

Ideal Gas law: P*V/T = constant . . .

You'd have to see a ~50% change in ambient temperature to account for that much of a pressure differential. . .

This. Even if the garage was at a freezing 0°C, that high of a pressure change would require a hot fill of 143°C (290°F). Not likely.

 

[JamesK]

I would tell him, "That's easy to rectify. You simply place your tanks in your vehicle for a few days before your dive on a hot summer day with the windows up. The pressure will go back up."

Fire the client immediately.

This. Do it NOW!

 

[captain]

The wet fill itself is not a problem, the problem is it not being done properly. It must be assured that the tank valve and filler whip can not be submerged to prevent the possibility of drops of water inadvertantly entering either the valve or filler whip before the connection to the tank is made. My wet fill bath has the tank standing vertically and the water level only reaches to the bottom of the tank neck. The filler is suspended by a cord that will prevent it from falling in the water if accidently dropped. That and cracking the tank valve and filler to blow out any water or other debris before making the connection asures I don't get any water blown into my tanks.
I have seen the shops that connect the fill whip to the tank and submerge everything in water, the next tank then gets connected to a fill whip dripping wet, sure way to get water in a tank.

 

[Wookie]

The wet fill itself is not a problem, the problem is it not being done properly. It must be assured that the tank valve and filler whip can not be submerged to prevent the possibility of drops of water inadvertantly entering either the valve or filler whip before the connection to the tank is made. My wet fill bath has the tank standing vertically and the water level only reaches to the bottom of the tank neck. The filler is suspended by a cord that will prevent it from falling in the water if accidently dropped. That and cracking the tank valve and filler to blow out any water or other debris before making the connection asures I don't get any water blown into my tanks.
I have seen the shops that connect the fill whip to the tank and submerge everything in water, the next tank then gets connected to a fill whip dripping wet, sure way to get water in a tank.

What Captain said. Wet fills CAN be done properly, they usually aren't. And, it really doesn't matter to the longevity of the cylinder or the adequacy of the fill. Fill at 50 PSI/min and the cylinder never heats up, and the fill is to the proper PSI, whatever that may be....

 

[chrpai]

What Captain said. Wet fills CAN be done properly, they usually aren't. And, it really doesn't matter to the longevity of the cylinder or the adequacy of the fill. Fill at 50 PSI/min and the cylinder never heats up, and the fill is to the proper PSI, whatever that may be....

Did you mean 50 PSI/min or 500PSI/min? Your point is valid but I don't know many (any?) shops that take nearly an hour to fill an AL80. I know Blackbeards had something like a 17cfm compressor that would take a couple hours to fill all the tanks. But when divers are off gassing during their SI, you're not really in a hurry anyways.