HP, LP? what this all about

[Darren27]

I have been reading some of the discussions on this board and was a bit confused. People have been asking about whether its best to get LP or HP steel tanks, whats the difference in ratings of these tanks. Also the size of tank is not what I am used to,eg 80,100,119s

Over in England we classify our tanks by their capacity and the working pressure in bar,eg a 12 ltr tank at 232 bar but I am curious as to how to compare between the two systems.

Thanks

Darren

 

[H2Andy]

ah ... i'll tackle the easy part ... let some one else do the conversions

over in the US, aluminum tanks are rated to 3000 psi, and come in a variety of sizes (from 6 cubic feet, to 40 cubic feet, to 80 cubic feet, and i believe a few 100's)

steel tanks come in two flavors, High Pressure (HP) rated to 3442 or 3500 (with other tanks coming in at over 3000) psi

and Low Pressure (LP) usually rated to 2400 psi or 2640 (2400+) psi

as i stated above, the size is given in cubic feet, so, for axample, an AL80 is an aluminum 80 cf tank, and LP104 is a low pressure steel tank at 104 cf, and an HP95 is a high pressure steel tank at 95 cubic feet

the cubic feet are measured when the tank is full to its rated capacity. for example, an AL80 will hold 80 cubic feet at 3,000 psi .... except it won't ... it will hold something like 77 cubic feet (but you can get a chart and look that up)

 

[Rainer]

We do nearly the same, just not in metric. A cylinder is rated to capacity at the working pressure (e.g. a HP80 would hold 80 cf of gas at 3500 PSI, or slightly lower for the newest HP cylinders; a LP80 would hold 80 cf of gas at 2640 PSI).

 

[Darren27]

Things are starting to become clear now. The main difference and where I was getting confused is the size you quote is the volume of gas at pressure held in the cylinder, where as we state the volume of gas at atmospheric pressure.

Our most common size is the 12 ltr steel with a working pressure of 232 bar
12 ltr cylinder at 232 bar (3364 ps1), that would be 2784 ltr of gas which is about 98 CuFt.

When your used to thinking that twin 12s are big, twin 100s kind of blow your mind:11:

Cheers

Darren

 

[H2Andy]

Things are starting to become clear now. The main difference and where I was getting confused is the size you quote is the volume of gas at pressure held in the cylinder, where as we state the volume of gas at atmospheric pressure.

so basically, when you say 12 ltr tank, the tank will hold 12 liters of unpressurized gas, right?

 

[merxlin]

When your used to thinking that twin 12s are big, twin 100s kind of blow your mind:11:

Cheers

Darren

Yeah, thats just how us studly divers on this side of the pond roll......Haven't you seen our new combo BP/W and sleeping bag? Our bottom timers are calendars.

 

[Luis H]

so basically, when you say 12 ltr tank, the tank will hold 12 liters of unpressurized gas, right?

That is correct. That is the actual volume inside the tank, not the volume of compressed air.


We rate ours by the volume of air (at standard temperature and pressure, "STP") that we push/compress into the tank.


Edit: What I don't understand is who the heck came up with calling a 2400 psi tank (or even an 1800 psi cylinder) a low pressure cylinder. Any thing over 40 psi (to maybe 150 psi by some codes) is high pressure by the Compress Gas Association and just about any agency or engineering organisation I can think of.

 

[spectrum]

While we're on capacity.....
Does the rated (US) capacity of let's say 100 cubic feet include the first atmosphere of volume that will never leave the cylinder except under a vacuum?

Yes I know this is nit picking but it just occurred to me that this must approach 1% on an 80 CF cylinder.

Pete

 

[Luis H]

While we're on capacity.....
Does the rated (US) capacity of let's say 100 cubic feet include the first atmosphere of volume that will never leave the cylinder except under a vacuum?

Yes I know this is nit picking but it just occurred to me that this must approach 1% on an 80 CF cylinder.

Pete

Take a guess.

 

[spectrum]

Take a guess.

Can I burn a lifeline?