HP vs. LP / High Pressure versus Low Pressure steel tanks

[matt t.]

It's generally easier to get a "full" fill with L.P. tanks (at least in my area). Not a big deal with $4 air fills, but not good with expensive Nitrox fills. I like the H.P. tanks because of their smaller diameters (H.P cylinders have a smaller diameter than the L.P.). If I was to buy again I'd look closer at the L.P. tanks.

Matt

 

[MikeS]

Check out the AquaAire Pro Low Pressure and AquaAire Sport High Pressure descriptions on the Pressed Steel Website at http://www.pstscuba.com/ .

Mike

 

[LUBOLD8431]

PST is about to start shipping their new E series tanks. There is no such thing as LP and HP anymore. They are all filled to a pressure of 3442 (230 bar). They will all be stamped with PST's E-9791 exemption. The only real difference is the diameter, weight, buoyancy, and also capacity. The PST website has NOT been updated to reflect the new cylinders... You will see the specs for their old cylinders... Look for the new ones in a dive shop near you!!!

 

[Lead_carrier]

Scubaroo once bubbled...
These terms are generally applied to steel tanks in the US.

LP = low pressure, typically either 2400 or 2640 psi (although tanks with even lower pressures down to 1800 psi are about)

HP = high pressure, typically over 3000 psi, with 3500 psi being common

An 80cf LP tank holds the same amount of gas as an 80cf HP tank (which, funnily enough, happens to be 80cf).

Comparatively, aluminum tanks are generally 3000 psi, 3180 psi or 3300 psi, and are not referred to as LP or HP.

Just a couple of minor nit-picks Scubaroo, no offense intended, HP is anything over 3300. AL or steel.

The 3180 psi you refer to is and is steel and made by Faber. It is considered to be HP only because of the 10% overfill. They tend to get confused with aluminum because they are thin and tall and look like an aluminum.

Just some trivia here. There are some HEISER tanks, their sizes are 120, 140, and 190. Their fill pressures are 3190 for the 120 and 140. A whopping 4400 for the 190. No I'm not kidding. The bouyancy characteristics rival lead. The one 190 is 87 lbs empty and 62 lbs negative full. It is 47 lobs neg empty. Think that will make you drop a couple of pounds off the old weight belt?

 

[Scubaroo]

Yeah, heard about the Heiser tanks, didn't know they were 4400psi though! They would make good ballast tanks for a home-built sub

 

[peterw]

I've been spending more time down deep and am looking for some extra air. I have been using AL80 as I have been for years but I want to stay down longer so I'm looking at 120 options.

High pressure (HP) tanks use DIN valve and low pressure (LP) tanks use yoke valve but can also use DIN. I use a DIN regulator so as far as that goes I'm good either way.

Some brands vary with the HP tank being a little smaller and lighter or heavier than the LP tank but LP tanks being a more expensive except for the faber tanks. Are faber tanks as good as the others?

Most dive boats can fill tanks to between 2900 and 3200 psi so it seems I can get about 120 from HP or LP tanks. With the HP tank I will have to keep an eye on the tank filler to make sure he gives me max fill. With the LP tank I will have to keep an eye on the tank filler so he doesn't explode my tank by accident. I wonder how much pressure the LP tank can really hold. If the tank filler over fills my LP tank I can get more than 120. I wonder how much more. I wonder if the LP tank will explode if it is filled with 3000 psi.

I'd love to hear any and all insight or recommendations.

Faber HP 120
Pressure rating: 3180 psi
Inches in Diameter: 7.25
Inches in Length: 28.6
Weight Empty: 45.4
Buoyancy Full: -16.6lbs
Buoyancy Empty: -7.7lbs
Price: $299.95

Sherwood HP 120
Pressure rating: 3500 psi
Inches in Diameter: 7.3
Inches in Length: 28.9
Weight Empty: 41.5
Buoyancy Full: -11.8lbs
Buoyancy Empty: -4.4lbs
Price: $314.85

Faber LP 120
Pressure rating: 2400 psi
Inches in Diameter: 8
Inches in Length: 29.3
Weight Empty: 45lbs
Buoyancy Full: -4.5lbs
Bouyancy Empty: 4.3lbs
Price: $299.95

XS SCUBA LP 121
Pressure rating: 2640 psi
Inches in Diameter: 8
Inches in Length: 29.3
Weight Empty: 45lbs
Buoyancy Full: -4.5lbs
Bouyancy Empty: 4.3lbs
Price: $422.85

 

[Atticus]

This has been discussed at length in other threads, but I'll try to give you a fair reply with my 2 cents...

First, it sounds like we agree that DIN is the way to go.

1. I prefer LP tanks because I can always get a good fill.

2. When doing partial pressure blending lower bank pressures are required, so it's more convenient (ie: it will be easier to get nitrox fills).

3. It is not uncommon for people to intentionally overfill LP tanks. While it would be unprudent of me to suggest that you do this, I can say that it has been often enough to strongly suggest that there is very little statistical risk when filling a good condition LP tank to say 3000 psi.

4. I personally would run for it if anyone tried to fill an LP tank to say ... 4000 psi in my presence. There are others who are comfortable with that arrangement.

In any case, I wouldn't panic about the possibility of people occasionally overfilling your LP tank.

Some would even say this is a good reason to buy an LP tank in the first place

You might reconsider buying 120cf tanks however. I would personally choose an LP 104 or 112. Both LP and HP 120's are a little oversized.

Best of luck with your decision whichever way you go.

 

[Mo2vation]

Fellow So Cal here.

I just went through this very issue, on this very board....and the light came on for me.

I dive an HP100 - love it. Great curb appeal (smaller, lighter, etc.) and dives great for me. When I'm filled on land, I get 3500 no prob...so I get 100 CF

Went through my log - for the last 8 - 9 months on the local boats (even the ones that state they can fill to 3500) I'm getting 2500 - 2800... basically getting 78 - 80 CF per location fill. So my first boat dive each trip is at 3500, while the others are at much, much less. Even if I grind the fill tech on the boat, I might get 3000. So on a 3 dive trip, 2/3'rds of the time I'm diving short. More on a 2 day trip.

Bummer.

I'm totally going to the e8-130 by PST. Sure, it weighs another 10 pounds over my beloved HP100. BUT, that's schlep weight (to the boat, from the boat...to the shop, from the shop...)

Its only an inch and-a-half taller, about 3/4" bigger around, I can likely drop another 3 from the belt, and it will deliver 20 - 25+ CF for each location fill... so I'll be diving 100+ CF for 100% of my dives, not 25% - 30% of my dives.

It totally makes sense to me to make this move. The peace of mind of more gas aside, I want more time...its that simple.

PST is the preferred way to go, IMO. I've dove the Fabers, and for my money, I know I'll get a longer life out of a Galv cylinder. I got the 130 for a good price, and I can't wait for it to come in! I'm not a big guy (5-8 178) and I've dove the E8-119's just fine. I'm confident the 130 will be fine. Its not the silo the E7-120 is.

Ken

 

[GP]

I have a couple OMS/Faber LP steel 85's. I've received sucky low fills everywhere I've gone except for at one shop who will actually fill them "full" 2640 or even 3000 if I request it. Everywhere else I go I end up with 2400 or less which really torques me off. It makes me wish I had aluminum 80's sometimes where at least I can get them filled full. My next tanks will be PST E130's.

 

[Atticus]

GP - Perhaps I should have said that the fill equipment will generally be capable of giving you a good fill unless the operator goes out of their way to do things too quickly or poorly.

Very few fill stations cannot hit 3000 psi due to the prolifigation of alu 80's.

Your fill operator may be incorrectly filling the tank to 2400 psi (ignoring the + designation), or may be filling too rapidly to 2640, giving you a significant pressure drop when the tank cools.

If you have a pleasant discussion with him you *ought* to be able to get good fills.

If he isn't aware of your tanks + designation then you should be able to simply point it out and ask for a 2640 psi fill.

If he just fills to fast and won't stop then have him overshoot your pressure. Say fill to 3000 psi then let cool to the neighborhood of 2640 (plus a little). A better answer is to just fill more slowly and/or top the fill after it cools a little.