Regulations concerning tank fills

[Dr. J.]

Is there a law or regulation concerning tank fills? Namely if the tank HAS to be filled with the tank in a water tub/tank.

One of the LDS here stopped filling tanks in the water. This does not sit well with me. I thought the whole reason for the water tank was to reduce the stress on the tank by keeping it cool.

One reason some LDSs fill in water is that they can fill quicker. A good LDS will slow fill the tank ensuring that the customer gets a good fill to the max rated pressure of the tank. Steel tanks heat up much easier than aluminum and have to be filled very slowly and often left to cool off to be topped up. If you get a tank filled make sure it is cool to the touch when you pick it up and even ask for a gauge to be put on the valve so that you can read the pressure.

 

[Eidolon]

Luxfer recommends a visual inspection every 12 months or 4 months for heavy use tanks: http://www.luxfercylinders.com/downloads/docs/scubaguide.pdf

FREQUENCY OF INSPECTION
A. NORMAL SERVICE. The visual inspection of every Luxfer scuba cylinder should
take place at least once every twelve months, or at any opportune time under twelve months. Some scuba cylinders need more frequent visual inspection, as indicated below.
B. HEAVY SERVICE. If the cylinder is used in heavy service then it should be
inspected every four months.
“Heavy service” means any one or more of the following:
1. Cylinders being filled or “topped off” five or more times per week;
2. Rental cylinders in use during the ‘season’ and ‘off-season’ times;
3. Cylinders used wherever damage is more likely than in normal use or where the
care and/or maintenance is slightly below recommended care.4
C. KNOWN CONDITION. If the cylinder is known to have had any unusual treatment
or condition, it should be immediately visually inspected, prior to its next use.

 

[mikswi]

LOL!! Yep

What people need to realize is that its very unsafe to fill a tank at a lower temp then it will be stored in.

Its important to know that for every degree in temp a tank changes, the pressure changes by 5psi. so, if you fill a tank during the summer in a "cool" liquid, then send it out the door to a customer at a full fill. Then he puts it in his trunk or in the direct sunlight while transporting it, there is a very REAL possibility that the burst disk could rupture.

Have a guy come back into the shop accusing you of not filling his tank and you will become familiar with these types of physics.

ever haver a burst disc falure when the tank is being wet filler?

you get wet

 

[android]

that because compressing air into the tank creates heat, you'll get a 'false' reading on the pressure gauge, i.e. the warm air is expanded showing, say 3000psi, let it cool and it may only be 2900 or less, depending on how fast you fill it.

It is not a false reading. That is the pressure at that temperature. If the temperature goes down the pressure will go down. If you don't put any more air in the tank the number of O2 molecules in the tank remains the same.

 

[D_B]

.... What people need to realize is that its very unsafe to fill a tank at a lower temp then it will be stored in.

Its important to know that for every degree in temp a tank changes, the pressure changes by 5psi. so, if you fill a tank during the summer in a "cool" liquid, then send it out the door to a customer at a full fill. Then he puts it in his trunk or in the direct sunlight while transporting it, there is a very REAL possibility that the burst disk could rupture ....

I don't understand this , in this case are you saying that the tank should only be filled to "rated fill" at a temp. of , oh lets say 130*F ???
Thats like saying that you need to check your tire press only after driving, so the tire is hot and you don't "overfill it" You check it cold, any press rise when hot is allowed and normal (even if It's "overfull" now that It's hot)
I thought that a tank was rated to X pressure - at X temp. Of course if you raise the temp above the rated press/temp. , then the press. will higher than rating = this is normal, and allowed. It's up to the tank owner not to expose the tank to extreme conditions that might cause the disk to blow

DB

 

[mikswi]

It's up to the tank owner not to expose the tank to extreme conditions that might cause the disk to blow

DB

Your last sentance says it all.

 

[Tigern]

Filling tanks in a water bath that is not cooled will only net you about a 45-60 psi gain in pressure. The best way to fill a tank is to NOT exceed the max fill rate. If you fill a tank at the proper rate you'll only drop about 75-100 psi. To compensate you fill the tank about 100 to 200 psi above the pressure stamped on the bottle. So since the standard tank pressures for AL80s are 3000 and 3300 so when we fill them we fill to 3200 and 3500 respectively. I've filled hundreds of tanks and have never had a complaint about a short fill and have had people come back and tell me thank you for a good fill.
oh and in case I wasn't clear, my LDS does NOT use a water tank for filling.

 

[android]

I don't understand this , in this case are you saying that the tank should only be filled to "rated fill" at a temp. of , oh lets say 130*F ???
DB

You get this automagically. The process of cramming air into the tank causes that air to be heated. Air is a terrible conductor, so even if the tank is cooled, the air inside will be much hotter for many hours until it all drops to ambient temperature. I'm not going to do the math, but I would guess it takes 12 - 24 hours for the temperature of the outside air = tank metal = air inside the tank.

Everyone is most interested in making sure the tank is full to rated capacity. It's really easy to make a spreadsheet that will show equivalent pressures for a range of temperatures. Use the combined gas law and the mfg's rated capacity.

P1*V1/T1 = P2*V2/T2

Pressure and volume can be any consistent units, but you must use Kelvin for temperature. K = C + 273 and C = (F-32)*(4/5)

Use the mfg specs to come up with a constant for P1*V1/T1 and then solve the other side for what you want to know.

 

[tedtim]

Any opinions on the meaning of the 2nd paragraph of the linked .pdf?
http://www.text-trieve.com/pdffiles/06977.pdf


John

The double negative "do not prohibit" statement is interesting. The statement does not specifically authorize filling of the tanks, but does not prevent them from being filled. The last sentence leaves a lot of room for discussion. If your LDS does not want to fill the tank, then they appear to be fully within their rights.

You had asked for a statement that "filling the tanks....is legal under Department of Transportaton regulations." The response provided did not say that.

My opinion. Even if you take a copy of the letter with you there will be fill station operators who will refuse the fill the tank.

 

[tedtim]

<<snipped>>

Its important to know that for every degree in temp a tank changes, the pressure changes by 5psi. so, if you fill a tank during the summer in a "cool" liquid, then send it out the door to a customer at a full fill. Then he puts it in his trunk or in the direct sunlight while transporting it, there is a very REAL possibility that the burst disk could rupture.

Have a guy come back into the shop accusing you of not filling his tank and you will become familiar with these types of physics.

The opposite is also true and commonly results in much discussion. When you dive in temperatures lower than the ambient in which the tank was filled, the pressure will drop in the tank as it cools. When the temperature drops to the mid fifty's, it is probably cooler outside too. So, the temperature of the tank will be lower than the 70F quoted as the spec for filling.

Then the whining about underfills really starts.