high pressure vs. low pressure

[FIXXERVI6]

[
HP 100 pumped to 3600 has roughly 105 cubic feet of gas
LP 108 pumped to 3600 has roughly 147 cubic feet of gas



Ok....Am I missing something here? Obviously so....because I ain't found anyone jacking a LP tank up to 3600.

Keep apples to apples. LP tanks are rated at approx 2440 and with a 10% hydro can go up to approx 2640. These tanks are therefore carrying their cu/ft of gas at their rated pressure. The same stands true for HP tanks. 100 cu/ft of gas at approx 3440.

The advantages of LP tanks VS HP tanks are that they have less weight for the same volume of gas. HP tanks tend to be a smaller package for the same volume gas and the manufacturers accomplish this by making the tank walls thicker in the HP tanks thus added weight. The HP tanks will also require the use of a DIN fitting instead of the standard yoke fitting. Many shops will have difficulty filling HP tanks to their rated pressures, and therefor one will not get their rated 100 cu/ft of gas at a fill of only 300psi. Some shops,due to their filling methods, will have difficulty blending nitrox mixes in HP tanks.

So why dive HP tanks. Again, it's all about hte weight:size ratio. Have you ever seen anyone with double LP 120's strapped to their back. Not too too many I would guess...and if so....I would address that person as SIR(even if they were a female).

The bottom line is this : 100cu/ft of air is 100 cu/ft of air...and it don't mean squat at what pressure you get that 100 cu/ft. You are better off deciding which tanks you want to dive (i.e. HP VS LP) and go that route rather than buying Lp tanks and jacking them up above their rated pressure.

it DOES mean squat as to what pressure I get 100 cubic feet at, because if I get 108 cubic feet at 2640, think about how much I get when I pump those things to 3600! its great!

lets see, double 120's, thats 240 cubes, my double 108's pumped to 3600 goes around 294 cubes, yup, 3600 in 108's works for me

The only high pressure tanks I would want are those with the same internal liquid volume of my 108's then I'd CRANK em, 3900 baby

Altho I'm crazy for doing so, so kids don't try this at home its dangerous

oh as far as burst discs I have my burst discs on my LP tanks setup for an operating pressure of 4300 psi

 

[limeyx]

[
HP 100 pumped to 3600 has roughly 105 cubic feet of gas
LP 108 pumped to 3600 has roughly 147 cubic feet of gas



Ok....Am I missing something here? Obviously so....because I ain't found anyone jacking a LP tank up to 3600.

Keep apples to apples. LP tanks are rated at approx 2440 and with a 10% hydro can go up to approx 2640. These tanks are therefore carrying their cu/ft of gas at their rated pressure. The same stands true for HP tanks. 100 cu/ft of gas at approx 3440.

The advantages of LP tanks VS HP tanks are that they have less weight for the same volume of gas. HP tanks tend to be a smaller package for the same volume gas and the manufacturers accomplish this by making the tank walls thicker in the HP tanks thus added weight. The HP tanks will also require the use of a DIN fitting instead of the standard yoke fitting. Many shops will have difficulty filling HP tanks to their rated pressures, and therefor one will not get their rated 100 cu/ft of gas at a fill of only 300psi. Some shops,due to their filling methods, will have difficulty blending nitrox mixes in HP tanks.
...

Actually, if you get an HP tank rated at < 3500 psi, then you can use a yoke (most tanks come with the valves with the "donut" in so that you can use DIN or Yoke).

I think over 3500 you need DIN.

However, the point about getting fills over 3000 is noted -- I sometimes get them, sometimes not. 300 psi seems a bit rotten tho

personally, I have an LP80 and HP-100 which are the same physical size, and generally they get treated interchangeably. The Lp80 I got from eBay $120. The HP 100 was more expensive (new). I usually end up with the same gas volume in them.

 

[CD_in_Chitown]

Actually, if you get an HP tank rated at < 3500 psi,

Less than 3500 PSI is an LP tank.

 

[akscubainst]

Less than 3500 PSI is an LP tank.

Anything over 14.7 PSI is high pressure as far as I'm concerned. In the right container (not a scuba cylinder) it doesn't take much more than that to kill you.

Using your logic though where do the 3442psi cylinders fit?

 

[FIXXERVI6]

Anything over 14.7 PSI is high pressure as far as I'm concerned. In the right container (not a scuba cylinder) it doesn't take much more than that to kill you.

Using your logic though where do the 3442psi cylinders fit?

My understanding of what the E8 cylinders use for DOT get by's is DOT requires 300 BAR valve on anything 3500 psi and up, PST put their's at 3442 to get just under that requirement which allowed them to go 200 bar which allowed din inserts so they could be used with yoke.

This is what I have been told and it makes sense to me

I consider anything over 3300 high pressure, just my opinion.

 

[limeyx]

My understanding of what the E8 cylinders use for DOT get by's is DOT requires 300 BAR valve on anything 3500 psi and up, PST put their's at 3442 to get just under that requirement which allowed them to go 200 bar which allowed din inserts so they could be used with yoke.

This is what I have been told and it makes sense to me

I consider anything over 3300 high pressure, just my opinion.

...and around we go

For steel tanks (what we are talking about), 2400 with a + is LP (just in my opinion) anything higer would be HP. Obviously some people think over 3500 is HP -- but I've never seen or owned a tank that is rated that high.

 

[FIXXERVI6]

...and around we go

For steel tanks (what we are talking about), 2400 with a + is LP (just in my opinion) anything higer would be HP. Obviously some people think over 3500 is HP -- but I've never seen or owned a tank that is rated that high.

in the realm of steel tanks only I guess that would be a correct view, anything over LP is HP, I agree on steels.

 

[UP4AIR]

All good points made here by everyone! And you Fixxer....I want to party with you...3900 on LP...You Go Boy! :bang:

The original question was turn around point as it relates to pressure. The turn around point will change as the use of Hp or LP changes as well as the 1/3 rule. However, regardless of pressure, it still goes back to the volume of the tank and not the pressure per say. What we are trying to achieve is 1/3 of our gas based on the size of our tank as it relates to the tanks pressure. Am I makin any sense at all here? If not you all jump in and go with it.

An 80 cu/ft tank at 3000 will have a 1/3 at 1000 psi and a volume of about 26 cu/ft.
A 100 cu/ft tank at 3440 will have a 1/3 at 1146 psi and a volume of about 33 cu/ft.

If we took that same 100 cu/ft tank and could get 100 cu/ft at 3000 psi, our 1/3 would still be 1000 psi but we would now have about 33 cu/ft of gas instead of our 26 with our 80.

 

[meekal]

as well noted above - is that the volume of the tank is based on the rated pressure. 80cuft is 80cuft - at the tanks rated pressure - but another point to consider - albeit small -

there may be occasion when you CAN'T get a fill to the tanks rated pressure - and yes, this pretty much only relates to HP tanks. so lets say you go on a llveAboard or on a mexican cenote expedition or some other 'out-of-the-way' place, with a funky ol' compresser - they might only be able to fill a tank to 3000psi.

saying the same thing as (FIXXERVI6 /Senior Member - page 1) but in a different format:

STEEL LP (2400) 80cuft = 100cuft [3000 / 2400 = 1.25 X 80 = 100]
Auminum (3000) 80cuft = 80cuft [3000 / 3000 = 1.00 x 80 = 80]
STEEL HP (3500) 80cuft = 68cuft [3000 / 3500 = 0.86 x 80 = 68.5]

it just gets real confusing because of all the different tank sizes....

 

[Hoosier]

The numebers have been played so many times in the previous posts.

Another follow up concern is whether or not you can get the right or overfill from your air source.