100cf vs. 90cf vs. 80cf: Big difference?

[Dash]

I have an oppurtunity to buy a used 90cf steel LP tank. I was wondering if anyone can make a edumacated guess as to the differences in air time over a 100cf or 80cf steel tank (or 72, if that is the standard)

What would 10 cf difference mean to you in air time. I realize the answer is based on individual breathing pattern and depth. Just trying to get a feel for the difference between them.

I was originally looking to get a steel LP 100. So depending on my feel for how it affects dive time (generally speaking) I may go with the 90 since its so cheap.


2nd question I just thought of. Lets say someone has a tank for sale that has good hydro and vis but the seller does not know much about the tank, ie, if it is HP or LP. Is there a way to tell? I would guess the answer lies in the tank code, but since Im a noob, I dont know that yet. IF there is a link to a primer on reading tank codes out there, Id appreciate that info.

Thanks!

 

[cameron]

say at 100 feet you would get an extra 3 minutes or so for every additional 10 ft3.... with a varience of 1 minute either way for good air consumption or bad air consumption...

The HP tank will have a higher rating for fill pressure, up in the 3400s...they are smaller and heavier
The Lp will have a fill pressure of around 2400...they are bigger and lighter....

You are right they are on the shoulder of the tank... go to any shop and ask about where the rating is and they will show you...

cheers

 

[Nautical Dreamer]

Like you said it is all dependent on your SAC rate and depth. But you can make a simple comparision based on volume %. A 100 cubic foot tank will give you 25% more air than a 80 cubic foot tank and a 90 cubic foot tank will give you 12.5% more air.

High preassure tanks will have a smaller diameter neck valve then a low preassure tank.

 

[Dash]

Thanks fellas....

 

[xiSkiGuy]

High preassure tanks will have a smaller diameter neck valve then a low preassure tank.

Not entirely true. Most current 3442 HP tanks (Faber, PST, Worthington) use the same valve as LP steels and AL tanks.

 

[meesier42]

I may be wrong here, but I believe he was refering to HIGH Pressure hoop wrap tanks, ie 4350 PSI tanks.

 

[rjack321]

2nd question I just thought of. Lets say someone has a tank for sale that has good hydro and vis but the seller does not know much about the tank, ie, if it is HP or LP. Is there a way to tell? I would guess the answer lies in the tank code, but since Im a noob, I dont know that yet. IF there is a link to a primer on reading tank codes out there, Id appreciate that info.

Service pressures are stamped on cylinders up at the neck.

Steel tanks will say 3AA (steel type),
a serial number
and a service pressure:
2250
3140
2400
3442
3500
are the most common.

Also
sometimes TP (test pressure) and a 4 digit pressure number
sometimes REE and a number (a hydro testing protocol code)

 

[xiSkiGuy]

I may be wrong here, but I believe he was refering to HIGH Pressure hoop wrap tanks, ie 4350 PSI tanks.

Or the 3500psi Genesis steel tanks. But neither is a common option for someone in the US who is deciding on what tank to buy. When most people (in the US, not Europe) refer to HP steel tanks, they are discussing the 3442psi tanks from Faber, PST, or Worthington. These all use the same valve thread as AL and LP steel.

 

[SparticleBrane]

I believe that's 3180, not 3140.

 

[spectrum]

Make sure the used 90 still has the+ or it's an 82.

Pete