Rated Pressure, 10% overfill, volume question

[GoBlue!]

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

 

[JimC]

There is no plus rateing (10% overfill) on al tanks.

 

[RichLockyer]

For steel tanks, the stated capacity ALWAYS includes the 10% overfill.
As Jim pointed out, aluminum tanks are never rated for overfill. A 3000psi S080 is a 77.4 at rated fill pressure, 3000... the S80N is 77.4 at 3300.

Steel tanks are a strange breed that leads to confusion. For example, right now, you can find two different steel tanks at Sport Chalet. One is a PST LP72, but it is a DOT3AA3000, so it is only a "72" when pumped to 3300. After it's first hydro and the plus goes away, it'll be a 3000psi tank at about 65cf.

The other tank is a Norris LP80. It is a DOT3AA2750... but as above, it only holds 80cf when pumped to 10% over at 3000. It'll be a 72 at 2750. This tank is a heavy beast.

 

[padiscubapro]

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

Aluminimum tanks should NEVER be overfilled. The rated capacity is at the stamped pressure. Overfilling Al tanks leads to premature failure (usually cracks around the neck). US dot ratings on steel tanks are very restrictive (compared to the rest if the world), and in general overfilling (within reason) them does little harm..

If you look at a tank that has both DOT and CTC ratings, the us rating (capacity) for the tank is sp +10% (and the plus is required) if the tank is filled in canada under the CTC banner the fill pressure is in bar and its the same as the us rating + the overfill pressure, so a "PLUS" is not needed in Canada (infact it means nothing, the stamped fill pressure IS the fill pressure)

 

[garyfotodiver]

Steel tanks are a strange breed that leads to confusion. For example, right now, you can find two different steel tanks at Sport Chalet. One is a PST LP72, but it is a DOT3AA3000, so it is only a "72" when pumped to 3300. After it's first hydro and the plus goes away, it'll be a 3000psi tank at about 65cf.

The other tank is a Norris LP80. It is a DOT3AA2750... but as above, it only holds 80cf when pumped to 10% over at 3000. It'll be a 72 at 2750. This tank is a heavy beast.

Steel tanks can receive the plus rating on any hydro, if the testing station knows the rules and does the extra work. There is a thread about this on the board.

 

[RichLockyer]

Steel tanks can receive the plus rating on any hydro, if the testing station knows the rules and does the extra work. There is a thread about this on the board.

I agree, but good luck.
Nobody in Southern California seems to be able to do it, and even if you DO have it, some shops accuse you of DIY with a screwdriver and hammer and still refuse to fill to 10% over.

 

[rab]

For steel tanks, the stated capacity ALWAYS includes the 10% overfill.

That's not true for the newer PST E-Series tanks. Those have a rated pressure of 3442psi and the capacity is at that pressure. There is no "+" rating for the E-Series tanks of which I'm aware.

-Rob

 

[RichLockyer]

That's not true for the newer PST E-Series tanks. Those have a rated pressure of 3442psi and the capacity is at that pressure. There is no "+" rating for the E-Series tanks of which I'm aware.

Correct.
That was the attraction to the HP series over the last few years. Unfortunately, they are getting harder to find than Elvis and Bigfoot, now that PST has scaled back scuba production.
There's a few left in the shops from past deliveries, but they are few and far between on filling new orders.

I've got three of the HP120s and hope they do not let the exemption expire.

 

[GoBlue!]

Thank you all very much for the clarifications.

jim

 

[DA Aquamaster]

Most hydro test facilites will do the testing required for a plus rating but only if you can provide an REE number for the tank. Faber has been stamping the number on there tanks which really helps. For other/older tanks, you may have to contact the original maufaturer to get the required documentation.

If you don't have the REE number, most facilites will not do the extra work required to plus rate the tank. They make their money on volume and there is little profit in spending the time to do the plus rating if the REE number is not readily available.