Rated Pressure, 10% overfill, volume question

[DWJ]

I was diving the outerbanks last week an I have a Faber Steel 100's with the plus rating. The dive shop consistently filled my tanks to 3200 not the 3500 they should be. So in effect I had a 92 not a 100. So why the plus rating? why not stamp the tank with the appropriate psi?

 

[BrianM]

I was diving the outerbanks last week an I have a Faber Steel 100's with the plus rating. The dive shop consistently filled my tanks to 3200 not the 3500 they should be. So in effect I had a 92 not a 100. So why the plus rating? why not stamp the tank with the appropriate psi?

There could be a lot of explanations as to why they filled to 3200. Did you watch them being filled or explain to them what you wanted? I usually wait while my tanks are being filled and I go over the type and fill pressure of each tank before they start filling. I have seen untrained employees who fill hundreds of AL80's all day just assume all tanks fill to 3000 psi...kind of irritating when you have an HP tank, scary when you have an LP tank!

As for why the + rating...I am sure someone who is in the business could answer that better, but I have always heard it was because the older steel tanks (like from WWII) had been rated too conservatively. The DOT or whoever decided it was safe to increase the fill pressure, but since the tanks in service already had the max fill pressure stamped on them, it would be confusing to stamp another max pressure on the same tank, so hence the +10% fill. I like the fact that the new PST E-8's dont have a plus, just a straight forward pressure rating, easy to understand and easy to explain to the dive shop tank-filler person

 

[ChrisA]

While doing some calculations this weekend, something came up & I started to question myself.

1. A Luxfer S080, rated pressure 3000, 77.4 cu ft.
- If overfilled to 3300, you actually have 85.1 cu ft gas (10% overfill), right?

2. A Luxfer S80N, rated pressure 3300, 77.4 cu ft.
- Is the rated 3300psig on these tanks including a 10% overfill? Or would an overfill actually be to 3630psi? I wouldn't want to get one of these tanks & after a hydro or two, lose the 10% overfill and end up with a 70.4 cu ft tank (3000psig).

Thanks,
Jim

Aluminum tanks are never rated for an overfill. If the tank can be filled to 3300 psi then 3300 is it's rated fill pressure. The "plus" stamp is something they do to steel tanks.

Standard AL80 tank holds 77.4 cu ft and it should never be overfilled

 

[roakey]

There's a lot of good information on the + rating, REE, DOT regs, etc here:

http://www.scubaboard.com/showthread.php?threadid=43936&s=

Roak

 

[DWJ]

There could be a lot of explanations as to why they filled to 3200. Did you watch them being filled or explain to them what you wanted? I usually wait while my tanks are being filled and I go over the type and fill pressure of each tank before they start filling.

No I didn't. After the first day we dropped the tanks off at the shop. Our group had over 28 tanks to be filled and some with nitrox blends. The next morning we picked them up and through a guage on them. I had the shop top the tanks off the but it was a zoo. Analyzing the blends etc.. and on a deadline to make the boat. The next day I checked and 3200 again but I didn't do a top off as the place was even worse because the nitrox divers ordered a blend and then the dive site changed and alot of tanks were to hot.