HP vs LP

[Sapper]

What are the significant differences between a Low Pressure tank and a High Pressure tank?

 

[em13]

guess you mean 200 or 300 bar, right?

Well you'll have a lot more air with a 300 bar tank.
But let's face the problem: most of the regulators, especially older than two years, are only built for 200 bar.
Before you get one of those 300 bar tanks you'll have to check, your first and second stage if they can deal with the 300 bar. Your dive shop can definitely tell you if your regulators are certified for 200 and 300 bar usage or only for 200 bar.

bye , EM13.

 

[simbrooks]

Moved to tanks/bands/valves forum for target specific audience.

WRT the question, LP are typically 2400psi rated, or plus rated to 2400+10%=2640psi (my psi's might be a tiny bit off), HP are rated at 3500psi, then you have the newer E Series rating which is 3442psi from PST.

LP walls are a bit thinner as are the E series from what i hear, than the HP tanks. People often pump them up to get more volume and again from users of those tanks this might only be good up to the first hydro when some wont fill beyond the plus rating. Some people say that pumping up is a timebomb, others disagree. For the same volume of air at rated pressure you have a smaller tank in HP. Due to the smaller size and thicker walls for the same volume HP tanks are seen as being a bit negative buoyant compared to LP and both of those a bit off compared to E Series which are mostly neutral when empty. I dive HP-120's, stupid heavy above water, but they have more than enough gas, fit me well, i bought them 15 years old spotless inside and anticipate them lasting longer than i will diving

 

[The Kraken]

Are you refering to the comparison between an aluminum low pressure tank and a steel high pressure tank?

If so, the significant difference falls in the displacement/capacity ratio.
For example, an aluminum 80 cu. ft. tank (Catalina), at nominal pressure, holds approximately 77.4 cubic feet of air. The tank itself is 7.25" in diameter and approximately 26" long.

A high pressure steel tank (PST E7-80), at nominal pressure, holds approximately 80 cu. ft. of air. This tank is 7.25" in diameter and approximately 20" long.

So, the aluminum tank, with a displacement of approximately 1073 cubic inches holds 77.4 cf of gas while the hp steel tank with a displacement of approximately 825 cubic inches holds 80 cubic feet of gas.

Therefore the aluminum tank holds .0721 cf per cubic inch while the steel tank holds .096 cf per cubic inch.

Also the inherent densities of the tanks are different resulting in a more negatively buoyant characteristic for the steel tank.

All of these factors go into resultant areas of required weight with different equipment configurations.

 

[simbrooks]

guess you mean 200 or 300 bar, right?

Well you'll have a lot more air with a 300 bar tank.
But let's face the problem: most of the regulators, especially older than two years, are only built for 200 bar.
Before you get one of those 300 bar tanks you'll have to check, your first and second stage if they can deal with the 300 bar. Your dive shop can definitely tell you if your regulators are certified for 200 and 300 bar usage or only for 200 bar.

bye , EM13.

Not sure what you are getting at here, yes 232 and 300 bar are the metric versions of LP and HP. Not sure if two years is a good cut off for a reg being able to handle more pressure, but it really is only the 1st stage that has to handle it, the second will take intermeadiate pressure of around 130-150psig. Although my regs are only a year old, the design is quite a bit older than that, maybe 5+ years. All you have to do is make sure you have a 300bar DIN connector on your 1st stage as there are 2 more threads on it than a 232bar DIN connector and so wont seal if you use it with a 300bar tank. 300bar DIN regs work with both types, you can get yoke type inserts with the E series tanks and use a yoke/a clamp style mount rather than DIN, this only works on 232 bar valves, 300bar is too deep to get the yoke over.

 

[jonnythan]

Do 300 bar tanks actually exist?

I wouldn't call 232 bar "low pressure" either..

 

[RDP]

What are the significant differences between a Low Pressure tank and a High Pressure tank?

There are many threads on this board that cover this. I hate it when people on the board tell me I didn't search for something. So, I'll try to hit the main points.

First, you have to understand the volume of gas a cylinder will hold. The "size" (volume) of the tank is given at a determined pressure. (example: 77.4cuft @ 3000psi) If the pressure is less than 3000psi you have less gas.


High Pressure (HP) tanks usually have their volume defined at pressures around 3500 psi. They are often lighter because or the higher pressure to volume ratio. They sometimes require din connections on your regulators. (I know some of you out there use yokes on HP tanks.) They are usually negative bouyancy at the end of dive.

Low Pressure (LP) tanks have their volume defined at pressures around 2400 psi. They are often heavier because of the larger due to their lower pressure to volume ratio. These too usually have negative bouyancy at the end of the dive.

You can take weight off your belt with both LP & HP tanks. HP tanks seem unbeatable, but there are some considerations. Not all fill stations can fill HP tanks to their rated pressure. Therefore, you will have less gas than rated. Any fill station can fill a LP tank to rated pressure. Din fittings are suggested with HP tanks. This is not a fault, but it will possibly require added cost to your equipment. HP tanks are usually more expensive to purchase.

Hope this helps.

 

[simbrooks]

Do 300 bar tanks actually exist?

I wouldn't call 232 bar "low pressure" either..

My nifty little convert thing tells me 232bar is 3364psi and 300 bar is 4351psi - so indeed i might well stand corrected on this, 230'ish bar would be close to our HP tanks in the US, but 300 bar is a bit stronger again and i hear available in Europe (i guess they have big compressors). Although the tanks i see in the LDS's are usually around 4000+ psi, sometimes just over 4500, so maybe they are 300bar. LP pressures of 2400psi are about 165bar just FYI, so they really are "low pressure". Even so all modern regs can take 3500psi quite easily, 4500psi might be pushing it a bit

Will go dig out some old threads using a search now and post them here for further info - why dont people search anymore? Here's some starters for you:
1 - HP/LP 2 - PST tanks 3 - HP/LP 4 - large debate on steel tanks 5 - about nitrox use
Enjoy

 

[jonnythan]

Will go dig out some old threads using a search now and post them here for further info - why dont people search anymore?

Why are the mods so grouchy these days?

 

[simbrooks]

Low Pressure (LP) tanks have their volume defined at pressures around 2400 psi. They are often heavier because of the larger due to their lower pressure to volume ratio. These too usually have negative bouyancy at the end of the dive.

Sometimes near positive, isnt the rated volume (or at least quoted volume by the manufacturers) at the plus rating?

You can take weight off your belt with both LP & HP tanks. HP tanks seem unbeatable, but there are some considerations. Not all fill stations can fill HP tanks to their rated pressure. Therefore, you will have less gas than rated. Any fill station can fill a LP tank to rated pressure. Din fittings are suggested with HP tanks. This is not a fault, but it will possibly require added cost to your equipment. HP tanks are usually more expensive to purchase.

I have yet to find this in a huge range of LDS's in FL i have taken tanks into. They might take a little longer or require them to have a full bank, but they should have that anyway. Swapping your connector out to a DIN from a yoke might cost about $50 at most (mostly for parts) and is quite quick. I prefer DIN anyway, but have an adapter for yoke so i can swap back on rental tanks if i am ever away from FL.