New Tanks?
- Thread starter Piston
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mossym
Contributor
given how popular the e7's are i'm not surprised!!
H2Andy
Contributor
ok, i've always wondered about this, so i figured i'd ask. i don't own any tanks, just
rent.
but my question is:
what is the difference between a high pressure and a low pressure tank?
rent.
but my question is:
what is the difference between a high pressure and a low pressure tank?
High pressure tanks generally are filled to above 3300 psi, low pressure tanks 2640 or below.
These might be PST tanks. I'd ask if anyone's seen them, but.. I know the answer to that already
These might be PST tanks. I'd ask if anyone's seen them, but.. I know the answer to that already
H2Andy
Contributor
jonnythan:
and i assume they are built differently to allow for the higher psi?
also, if i have a 3000 psi AL 80, i can assume it's high pressure?
so what are low pressure tanks used for?
3000 psi isn't generally high or low pressure.H2Andy:
As it's commonly used, "HP tanks" have a 3500 psi service pressure, whereas "LP Tanks" have a 2400 psi service pressure. These are both generally steel tanks. The LP tanks sometimes have a "+ rating" which needs to be renewed via hydro which allows for a 10% overfill, yeilding a 2640 psi service pressure. Faber, OMS, and PST low pressure steel tanks are rated at their fill volume at the plus rating. A PST LP 95 holds 95 cubic feet at 2640 psi. Cavers are known for using the LP steel tanks and filling them to well over 3000 psi to get tons of gas, hence the term "cave fill" for a gross overfill.
HP steel tanks, in the past, were most often 7.25" in diameter (same as an Al 80), as opposed to LP steels which were 8" in diameter. For various reasons, tech divers have apparently preferred the LP tanks because of their buoyancy and trim characteristics over the narrower HP tanks.
Recently, however, PST has created HP tanks, with a 3442 service pressure, which are very similar to their old LP tanks.. essentially, now you have the best of both worlds: high service pressure with favorable buoyancy and trim characteristics. These are PST's E8 series of tanks.
bedmund
Contributor
H2Andy:
Generally aluminum tanks aren't designated high or low pressure, just steel. A while back, fill stations that could fill a tank consistently above 3500 psi weren't common. That's not really the case anymore. High pressure tanks use a DIN connection and there's a line of reasoning that says low pressure is easier on the first stage than high pressure.
-Bill
bedmund
Contributor
... and sir Jonnythan types faster than me.
All HP 3500 tanks require a dedicated DIN valve. The new PST E-7 and E-8's have the combination DIN with the screw in adapter for use with a yoke regulator.
Low pressure steel tanks of 95 cu. ft. and larger are all 8 inches in diameter. While the HP tanks and Aluminum are all 7.25 inches. Because of the bigger internal volume you are able to get more gas in the tank with a lower pressure.
All steel tanks actually hold their rated volume as opposed to the 80AL that holds 77.5.
The steel tanks have several advantages for me:
They are negative at the end of the dive so my rear end does not float like it does with an AL 80.
Second is the amount of gas they hold for their size. My PST HP 100's hold 100 cu. ft. of air at 3500 are nearly three inches shorter than my AL 80's and holds 25 percent more air but they weigh nearly the same.
As Johnny said cave divers and tech divers prefer low pressure tanks because they can mix gas easier and the tanks can be easily overfilled.
In Cozumel I dive a PST LP 95 full at 2640. It's always filled to 3000 and give me nearly 108 cu. ft.
Low pressure steel tanks of 95 cu. ft. and larger are all 8 inches in diameter. While the HP tanks and Aluminum are all 7.25 inches. Because of the bigger internal volume you are able to get more gas in the tank with a lower pressure.
All steel tanks actually hold their rated volume as opposed to the 80AL that holds 77.5.
The steel tanks have several advantages for me:
They are negative at the end of the dive so my rear end does not float like it does with an AL 80.
Second is the amount of gas they hold for their size. My PST HP 100's hold 100 cu. ft. of air at 3500 are nearly three inches shorter than my AL 80's and holds 25 percent more air but they weigh nearly the same.
As Johnny said cave divers and tech divers prefer low pressure tanks because they can mix gas easier and the tanks can be easily overfilled.
In Cozumel I dive a PST LP 95 full at 2640. It's always filled to 3000 and give me nearly 108 cu. ft.
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