hp vs lp

[Leadking]

Most HP tanks do not use a DIN valve but a convertible valve for yoke or DIN (200 bar) connection.

 

[iztok]

An LP95 holds 95cu' of air at 2640. But if you fill it to 3600 it holds 130cu'. If you fill it to 4k (which is very common for the past 2 decades in N. Florida) it holds 144cu' of air. Lets see an HP119 due that. HP119 at 3442 = 119, at 3600 = 124cu' and at 4k (if you're dumb enough to do that) = 138cu' of air.

XS Scuba Worthington Steel Cylinder Specifications is my source.

LP95 at 2640 - 93.3 cft
HP119 at 3442 - 123 cft

At 3600 - 127.2 and 128.7 respectively.
At 4k - 141.4 and 142.9 respectively .

Basically at the same pressure they are the same capacity with HP slightly lager based on manufacturers specs.

 

[mathauck0814]

For arguments' sake a LP109 is roughly the same dimension as a HP130. I believe that the HP130 weighs more empty because te walls of the tank are more robust. I've heard of folks replacing (doubling-up) the burst discs on the LP109 and cramming 4000+psi into it - at which point it carries more air than the HP130. Probably not applicable unless you're expedition diving, and certainly not the safest method - but it's one reason I've heard folks picking LP tanks.

I personally own 8 HP tanks because we do lots of shore diving and the smaller format and lighter weight are beneficial (also diving in cold water with a drysuit the negative properties get lead off the waist).

 

[iztok]

For arguments' sake a LP109 is roughly the same dimension as a HP130.

I think that when we talk about capacity at the same pressure point best option is to use these tables in metric. (and use liters as a guide which tank packs more at the same pressure)

XS Scuba Worthington Steel Cylinder Specifications

HP 119: 14.8 liters
HP 130: 16.0 liters

LP 95: 14.8 liters
LP 108: 16.8 liters

Basically what we see that internally HP 119 and LP 95 are the same size thus at the same pressure they should hold the same amount of gas. LP 108 is 5% bigger than HP 130 thus holding 5% more gas at the same pressure.

 

[edgpr]

Excuse my lack of knowledge, I'm a beginner currently also trying to decide what to buy. Those calculations look awesome, and going by them I would buy an LP tank since they can carry about the same as an HP (at same pressures) and they cost less, but here is my dumb question. Isn't the rating "LP" exactly what it means? I had assumed that an LP tank rated at 2400 psi couldn't be overfilled past that pressure, hence the purpose of rating it LP. What I see here is that I can SAFELY overfill a LP tank past its psi rating? If this is the case, then why are they rated LP ? Then whats the point of having different ratings? buoyancy only?

 

[aquaregia]

The HP vs LP debate is really two comparisons:

1) For constant capacity
2) For constant volume

Consider these three tanks: HP100, LP95, HP119

1) LP95 vs HP100
- LP95 is physically larger and heavier
- LP95 is cheaper
- LP95 is always ~100cf, whereas the HP100 could be underfilled

2) LP95 vs HP119
- LP95 is cheaper
- LP95 might only be permitted to fill to 2640

The final consideration is that almost all HP tanks are exemption tanks, which might not be renewed. However, the 3AA tanks can lose their + rating. Neither of these are particularly likely.

For me, I run entirely LP tanks. LP tanks are more likely to be found second hand than HP tanks, so the cost factor is significant. As a bigger guy, crosscomparison 1 will lead me to buy the LP tank because I'm happy to carry the bigger tank. However, if I was buying new tanks, I'd be buying by form factor, not capacity, so crosscomparison 2 would probably lead me to the HP tank.

 

[boulderjohn]

E Isn't the rating "LP" exactly what it means? I had assumed that an LP tank rated at 2400 psi couldn't be overfilled past that pressure, hence the purpose of rating it LP. What I see here is that I can SAFELY overfill a LP tank past its psi rating? If this is the case, then why are they rated LP ? Then whats the point of having different ratings? buoyancy only?

Well, um....

LP tanks are usually rated to be filled 10% above that rated pressure, so they can officially be filled to 2640, and you are officially not supposed to fill past that official pressure.

Officially.

The reality is that they are overfilled well past that routinely, especially in cave country in North Florida. The first time I had my LP 108s filled in cave country, I was not asked what pressure I wanted--they just got filled to 3,700 PSI. I have never taken them anywhere in cave country that did not fill them to at least 3,500.

What about outside of cave country? For the deco diving I was doing this year in south Florida, the shops where I had them filled assumed I wanted 3,000 PSI. They asked, but that was the starting point.

So, once again, you are officially supposed to stop at 2640, but I don't know anyone who does.

 

[edgpr]

Thanks for all the clarifications. So the message I got was right. You can only overfill them 10% "officially" but its a common to practice to go past that without any known problems. Tx, that changes my view on LP tanks a bit.

 

[Otto]

The tank to purchase nis the one that you can drag into the water/ boat and back out of the water on your own while providing the gas supply needed and boyancy characteristics that fit your frame. Keep in mind that if doubles are in your future that may effect your decision. Please also note that a benefit of LP cylinders that has not been mentioned is that the blending of dive gas at home without a compressor or a Haskel is significantly easier with LP cylinders.

Best regards and dive safely.

 

[imwright1985]

cavers will overfill LP tanks and with their cost it makes them better then a HP tank. most normal shops wont cave fill a LP tank so if you want volume for tank size go HP permitting your LDS can fill that high.

Typical "tank monkeys" will fill to 3k on any tank not thinking twice. My location I can get HP fills easy and the shops wont overfill LP tanks, so I am looking to buy HP