Why wont my shop give me 10% overfill?

[Iceguy4]

I just picked up 2 new Worthington Low Pressure Cylinders LP8-121 Steel Cylinder tanks rated at 2400 psi. there is a star next to the numbers indicating 10% overfill. Its my understanding that these tanks are 109 cf without the overfill. When I picked up my new tanks at the shop after 44+ dollars for 2 visual inspections (rip off...stinking new tanks) , when I dive the tanks were both at aprox 2390 psi! When I talked to the shop he said "oh no that is for the hot fill and they are ment to cool to the rated 2400 psi."( I didn't buy the tanks at this shop) Before I got these tanks a buddy had the same tanks @ 27. 2750 psi from his shop. I am an air hog and need the extra air to not shorten my buds dive. I'm not looking to overfill the crap outta these tanks but if they were ment to be overfilled 10% , then I want it. Its getting to the point where I'll buy a compressor if I need cuz I getting sick of short fills.

 

[David P]

the star stamp does not mean 10% overfill a "+" mark does. The star signifies that if it is a stationary tank (scuba doesn't qualify) that it only needs hydro every...10(?) years.

 

[letterboy]

. . . can you get us a picture of the stamp iceguy?

 

[Iceguy4]

This is a copy of the tank description from the company where I picked them up...

Worthington Cylinders - Scuba Cylinders - Low Pressure 108 CF Steel Cylinder
NOW WITH HOT DIPPED GALVANIZED FINISH!
The shortage of steel scuba cylinders in the United States has greatly eased with the introduction of Worthington Cylinders Company's new line of low pressure steel scuba cylinders. As the world's oldest and largest supplier of industrial steel cylinders, Worthington was well positioned to move into the scuba market. The Chromium Molybdenum construction of these cylinders, along with the 2400 PSI pressure rating, provides you with a compressor-friendly cylinder rated at a pressure that guarantees full fills at any scuba fill station. Designed to be negatively buoyant throughout the dive - full or empty, the Worthington Low Pressure Steel Cylinders offer the standard 3/4"-14NPSM neck thread found on all aluminum scuba cylinders in the United States. For added resistance to rust and damage, the Worthington low pressure cylinders now have a hot-dipped galvanized exterior finish. This cylinder is manufactured to the DOT 3AA scuba standard and meets all specifications of the Canadian TC3AAM standard. All Worthington Low Pressure Steel Cylinders are supplied with the Thermo PRO convertible DIN/Yoke valve and a black rubber boot.



Volume: 121 CF at 2640 PSI

 

[Iceguy4]

http://www.divesports.com/IndexPages_Cat/cylinders_cat.htm

This is the link to the site wher I got them. The tanks are at the shop now but I will get pic if you still need it. I assumed these were rated for an overfill.

 

[letterboy]

http://www.seapearls.com/tanks-steel.html
This is straight from the horses mouth. . . I would talk to the shop again if they still don't believe you print off that table from sea pearls and show them it not sure how many shops are near you but you may want to be careful not to $!!t were you eat, I know off only one shop in my area. . . Now this isn't meant as a roll over and let them walk on you. . .

 

[oxyhacker]

Your shop may be confusing the overfill some sources say are allowed to do to compensate for temperature with the 10% "+" overfill allowed under 173.302a(b). Or they may just be incurably wrong headed.

The regs do make an exception for overfilling to compensate for temperature, but it has absolutely nothing to do with the "+" overfill. CFR 173,301a(c) says that a tank is filled when it is at its rated service pressure (or allowable filling pressure for a "+" rated tank) when it is at 70 degrees. This is generally taken to mean that it can be filled to a higher pressure when at a higher temperatures as long as it is not filled so high that it will be at higher than the rated pressure when it cools down.

The tricky thing about ovefilling for temperature is that the regs don't tell how much, so the filler has to figure it out. Some older sources say you can overfill 10% but this is usually much to generous. The right way would be by measuring tank temperature and doing a little math, but most shops which care do by rule of thumb adding 150 psi or so or using the "5 psi to 1 degree" rule which, while an approximation, works well enough.

You'll probably have a have a hard time convincing your shop of this, though. You could try showing them the applicable CFRs (you can download them), but they take reasonable intelligence to interpret.

Of course if your tanks are really marked with stars rather than "+"s, that's a whole new story...

 

[Luis H]

Your shop may be confusing the overfill some sources say are allowed to do to compensate for temperature with the 10% "+" overfill allowed under 173.302a(b). Or they may just be incurably wrong headed.

The regs do make an exception for overfilling to compensate for temperature, but it has absolutely nothing to do with the "+" overfill. CFR 173,301a(c) says that a tank is filled when it is at its rated service pressure (or allowable filling pressure for a "+" rated tank) when it is at 70 degrees. This is generally taken to mean that it can be filled to a higher pressure when at a higher temperatures as long as it is not filled so high that it will be at higher than the rated pressure when it cools down.

The tricky thing about ovefilling for temperature is that the regs don't tell how much, so the filler has to figure it out. Some older sources say you can overfill 10% but this is usually much to generous. The right way would be by measuring tank temperature and doing a little math, but most shops which care do by rule of thumb adding 150 psi or so or using the "5 psi to 1 degree" rule which, while an approximation, works well enough.

You'll probably have a have a hard time convincing your shop of this, though. You could try showing them the applicable CFRs (you can download them), but they take reasonable intelligence to interpret.

Of course if your tanks are really marked with stars rather than "+"s, that's a whole new story...

There is also a 130 degree F limit. I can’t recall were I read this, but I think it is from one of CGA documents that CFR49 refers to.

Doing the math for the 130 F:
(130F + 460 R ) / (70F + 460R) = 1.113
Therefore a maximum of 11.3% overfill to compensate for temperature (at 130 F). But 130 F is very hot. IMHO when filling a tank you should never allow to get that hot.


I recall seen the meaning of the “star” stamping (not the “+”, I have a copy of CFR 49 section 173) in one of the documents, but I cant find it now. I can’t even remember what it meant. Do you know what it means and the document (CFR or other) were it is described.

 

[roakey]

I recall seen the meaning of the “star” stamping (not the “+”, I have a copy of CFR 49 section 173) in one of the documents, but I cant find it now. I can’t even remember what it meant. Do you know what it means and the document (CFR or other) were it is described.

The star rating on a cylinder allows the cylinder to be hydrostatically tested every ten years instead of every five. However, a requirement comes with that star -- the cylinder must be hammer tested before each and every fill. Many dive shops have star ratings on cylinders in their banks, not realizing that they're breaking the law, because they're not hammer testing between each and every fill (which would be every time they run the compressor).

Basically, a cylinder in a bank MUST be tested every five years, star rated or not.

Roak

 

[oxyhacker]

Actually the latest CFR has gone somewhat metric so it's now 131 F or 55 C, that being the highest heat the regs allow filled tanks to be transported at. 179.301a(c)(2) puts a top limit on both temperature and pressure, saying that the pressure at 55/131 cannot exceed 5/4s of the allowable fill pressure at 70.

There is also a 130 degree F limit. I can’t recall were I read this, but I think it is from one of CGA documents that CFR49 refers to.