Tank Question??

[Prater]

My wife uses much less air than me and hates to end a dive early so I am thinking of a pair of 100 or 120 tanks to help extend my time underwater. I will be using them as singles.

What is the difference in the low pressure and high pressure steel tanks?


Thanks in advance

[fernandezh]

I know there are guys here who can proboly answer this question in more detail than I can but here goes.

Low pressure tanks are rated to be filled here in the USA to 2400 psi. and often to 10% over that. There are dive shops who will replace the burst disks in the LP tanks and fill them up to 3500 psi to give the diver more air. For example, if a LP tank holds 100 cu ft of air when filled to 2400 psi. . . then the the same LP tank will hold 145 cu ft. of air when filled to 3500 psi. There is a lot of debate over the safety of filling an LP tank to 3500 psi and most dive shops will not do it out of safety concerns for their employees. Another factor concerning LP tanks is that they have a larger diameter than High Pressure (HP) tanks which cause problems in tank racks as most only hold the smaller diameter HP tanks.

Another common, yet not exclusive difference between LP and HP tanks is that LP tanks often come with a yoke valve while HP tanks often come with a DIN valve. The difference in valves might cause you to have to change regulator setups or buy adapters, depending on the type of regulator you already have.

There are also bouyancy differences between the two which I will not go into cause it makes my head hurts just to think about it. Anybody else want to add to this?


Hector

[Prater]

Thanks Hector,

Looks like the HP tanks would be a better investment, even if I have to use an adapter for my gear. I do not want to convert LP to HP tanks. Just wondering why people would want LP tanks.

[rusty]

More bottom time, I just traded a HP120 for a LP125

[WreckDiver]

PST E series E7-100 or E7-120 is the only way to go your gear will fit.. 3440psi DIN/K valve.

[kitefisherman]

If all that you are trying to do is get a tank that will let you keep up with your wife (who is presumably diving AL80s), a HP120 (3500 PSI or 3440PSI) should get the job done. The 3440 PSI tank will allow you to dive the tank with a yoke reg so that you don't have to convert it or buy a new reg.

On the other hand, if you want maximum CFT, IMO LPs are the way to go - and you can still use your yoke reg if you want.

[Prater]

OK,

I am now confused. Sorry I dont have much experience. The LP tanks hold more air at lower pressure?? So HP tanks would be for deeper dives?? Around here our normal dive is only 30 feet because of poor vis and cold thermocline, but I hope to be on the coast in the next couple of years and want to buy smart.

Maybe I should just avoid the confusion and buy one HP and one LP.......:D

[kitefisherman]

Prater:

A LP tank's volume is determined by how much air it will hold at 2400 PSI. A HP tank's volume is determined by how much air it will hold at 3500 PSI. A 100 CFT HP pumped to 3500 PSI will hold 100 CFT. A 100 CFT LP pumped to 3500 PSI will hold 145 CFT (100 x (3500/2400)). Athough the LP is rated at 2400 PSI, it's service life is 10,000 fills to 4000 PSI per the manufacturer; accordingly, many people and dive shops fill them like a HP steel tank.

You might want to check with your local dive shop for tank availability, pricing and fill pressure before you make your decision.

[FredT]

The "rules" changed for the better this year.

The new PST E series gives the valve, volume and buoyancy advantages of an overpumped LP with the choice of available diameters and buoyancy specs common to the older HP tanks, all while keeping things "legal".

If buying new steel tanks they seem to be a no brainer, although WHICH E tank is still a matter personal buoyancy and volumetric needs.

If buying used tanks all the old saws apply.

FT

[Prater]

Local dive shop suggested LP if I want a quick fill or HP if I dont mind dropping off the tank to have it filled. i may just get an E7-100 or 120 for now.

Thanks for the suggestions. If anyone has a good larger capacity tank they may want to let go please give me a PM, I am always looking for a good bargain first.

[junior]

Buy her a 63 and keep your 80 unless you are planning on doing a lot of deep nitrox type stuff.

[Prater]

Junior,

That was my first thought, but I want to extend my bottom time. I got a hell no from her when I asked if she wanted smaller tanks.

picky woman

[bgbill]

I have HP 120's and LP 121's, I prefer the LP's over the HP's, the reason's are as follows

Easier to get full fills

I regularly over fill them for greater capacity, never had a problem with hydro.

My LP's are rated for 10,000 cycles @ 4,000 psi

they have better boyuancy characteristics

do not rust as easily as HP's

If you do not overfill them they aren't as rough on your regulator's.

My valves have 200 bar din or can accept yoke adapters.


The only advantage I can see on a HP it is slightly lighter to haul around than my LP 121's, and doubled up they are pretty light compared to LP 121's.

I have 3 HP 120's that I would be willing to trade for either faber LP 120's or OMS 121's.

[TGuthrie]

If you are concerned about full fills on the HP tanks, that is nothing that you should have to worry about. As long as you do not except a very hot tank after the shop fills it you should not have a problem. I know there are a few shops in the area that do not fill in a tank of water and that is where you might run into a problem because temperature has a great effect on tank pressure. If you decide to go with the LP tanks you, and are you are going to rely on the over filled tank for the greater capacity, you need to understand that not all shops are going to do that for you. Pressed Steel has came out with the new E-series tanks, some of wich are the old LP tanks at a service pressure of 3442psi wich will give you the extra volume without having to deal with finding someone to overfill them.

[kitefisherman]

I went back to the PST site (http://www.pstscuba.com/) again today, and they still do not have any info on the E series tanks. All I have heard is rumors. I'd like to see some specs on dimensions, PSIs, weights, buoyancy and volumes. I'm hoping that the E series can give me the same volume of air that I'm getting with my LPs now but with the legitimacy of filling the tanks to the higher PSIs. However, most of what I have heard indicates that they have just reduced the HP's PSI rating under 3500 PSI so the tanks can accomodate yoke valves. I have respect for what FredT says, but I'd still like to see the specs on the PST website and actually see the tanks that live up to the claims actually arrive in my LDS. Until then, I'm old school.

[DeathFromAbove]

I dove last weekend and did a head to head comparison of the HP120s I just bought and my buddy’s LP 95s. The 120s were filled to 3500 PSI and so were the 95s. Math says the LPs were a total of 138 vs. 124 for the HPs. Bottom time basically the same (as you would expect) and a little more than 1.5X an equivalent dive with and 80 (again as you would expect). I had too much weight for either tank as I am still getting use to them but the buoyancy seemed similar. The LP is a little bigger around and had no problems adjusting my BC to fit either. I dove with my pony on each dive and didn’t seem to matter much which tank I used as the main. The LPs are a little shorter and which made them easier to deal with on the boat while getting on all the gear. The 120s are a little taller than the 80s and I could notice the extra height as I was walking around with the gear on before and after the dive. My buddy bought the LPs a couple of months ago and the retard at the LDS didn’t swap the burst disks. They were in the back of my truck a few weeks ago when one went off. It was really nasty and someone could easily been seriously hurt so be very careful. The burst disks were upgraded and he has a good LDS that he uses now that overfills the tanks with no problems. If I were to buy another tank, I probably would consider the LP120. If you can get the pig overfilled you are talking about some serious bottom time. I haven’t had the experience of others to know how hard it is to overfill the LPs but I bought the 120 HPs because I didn’t want to deal with it.

I think if you get the HP120s, you will solve your problem. I got mine at Diver's Direct in Orlando for $270 each.

[Prater]

I purchased an E7-120 from Sharkbait here on the board. I do not want the hassle of trying to find someone to overfill any LP tanks. Thanks for the responses.

[bgbill]

I think you guys misunderstood why I over pressurize Lp's, it is to get more gas.

You do not breath psi

If you are looking for a tank with 120 cu ft of capacity the LP's are a better option in my opinion.

Lower pressure= easier to get a full fill without over pressurizing, but if you need to get more capacity you can over pressurize them.

Lower pressure is easier on the regulators.

You can use din or yoke, I prefer din.

less problem with internal rust on a LP.

I don't need a weight belt with a LP 120 and a SS back plate.

[Prater]

bgbill,

If I had low pressure tanks that I wanted overfilled should I buy low pressure valves or high pressure valves?? I understand what you are saying, I just dont know if a local shop would overfill them here in Oklahoma...

[WreckDiver]

You would Have to find a local diver with his own compressor!

[joens]

Prater , I am sure there is a shop in OKC that deals with cave divers as you are relatively close to the caves in missouri.
Joens

[bgbill]

Originally posted by Prater
bgbill,

If I had low pressure tanks that I wanted overfilled should I buy low pressure valves or high pressure valves?? I understand what you are saying, I just dont know if a local shop would overfill them here in Oklahoma...

The burst disc needs to be changed in the LP valve, the valves have different diameter threads for HP and LP.

Some shops will overfill them, some won't.

I get my HP's and LP's filled to 3800 psi on a regular basis, even the shops that do not like to over fill tanks will usually fill LP's to 3000-3200 psi.

There is nothing wrong with HP's I think the LP's are more versatile, I own Several HP's and Several LP's, I also have a bunch of AL 80's that I am going to get rid of.

I have my own compressor that needs to be repaired and then I won't have to worry about getting the fills that I want, I already have an 02 bottle and then I will get a He bottle and then I can blend my own trimix.

[WreckDiver]

That the way to go. mix you own gas:)

[Dangerous]

PST Specs

[Slackr]

Why are the HP tanks more prone to rusting? I assume it's different metal than the LP.

[bgbill]

Originally posted by Slackr
Why are the HP tanks more prone to rusting? I assume it's different metal than the LP.

I am assuming the same thing, Rene my Instructor said it also has to with the higher partial pressure in the HP's, but I would assume the same thing should happen to LP's when over pressurized, I have not had as much problems with LP's rusting and the HP's have not been that bad.

[bgbill]

I don't think there is anything wrong with HP's, I just think the LP's are more versatile.

I just bought another set of Pressed Steel HP 120's for $400.00 yesterday, that are doubled up, with an OMS Isolator 300 bar Manifold and Bands.

If my wife starts diving she can use the HP 120's, they are actually lighter than the Al 80's that I have.