LP vs HP

[Mark Michaud SELAUSAR]

If you can get a fill to that level, then why not get an HP tank? Do they also fill HP tanks to 4800 psi?

Again, Volume does not equal pressure. A LP tank, say a 95 if the volume is 2400 psi, then at 2400 psi you have 95 cu ft. of gas.

Some tanks are marked 95, 98 etc, and the actual volume may not be the actual marked voume. For the sake of this analogy 95 cu FT. LP at 2400 psi equals 95 cu. ft of gas. A HP 95 takes 3442 (sake of arguement PSI and Volume) to obtain the same volume of gas.

If the same LP 95 was filled to 3600 the volume will increase and give you much more volume (50%?) than 95 cu ft. coming to about 140 cu ft. For a hp tank to get to the same volume as a lp tank of the same capacity, you have to have higher pressure.

 

[merxlin]

Again, Volume does not equal pressure. A LP tank, say a 95 if the volume is 2400 psi, then at 2400 psi you have 95 cu ft. of gas.

Some tanks are marked 95, 98 etc, and the actual volume may not be the actual marked voume. For the sake of this analogy 95 cu FT. LP at 2400 psi equals 95 cu. ft of gas. A HP 95 takes 3442 (sake of arguement PSI and Volume) to obtain the same volume of gas.

If the same LP 95 was filled to 3600 the volume will increase and give you much more volume (50%?) than 95 cu ft. coming to about 140 cu ft. For a hp tank to get to the same volume as a lp tank of the same capacity, you have to have higher pressure.

I'm quite familiar with the volumeressure issue. My point was why fill a tank rated at 2640 PSI to 3900 PSI. The argument for LP tanks has typically been that for lower pressure capacity fills, you can get more volume, i.e. if the shop can only fill to 2400 psi, you get a 90% fill on an LP+ versus a 75% fill on an HP with the same volume.If you can get higher pressure fills, why not use a tank rated for that pressure versus one that is not. Get it?

 

[Mark Michaud SELAUSAR]

I prefer to dive (sidemount) with lp 85's. A normal "cave fill" allows more volume without having to carry a stage. Most places a normal cave fill is 3600 psi. After many years LP steels have proven that they are more than capable of handling this pressure and still pass hydro's. It has a great safety record as well. No exploding steel tanks or catastrophic failures as with al 80's of a particular composite.

Again it is a preference of tanks, but the original post in this thread seemed to be about volume and pressure. Bottom line rated pressure on any tank is necessary to achieve marked volume. Hence with a LP bottle you can raise the pressure and get more volume. If size and convenience and strictly rec. dives are your preference than HP steel have a lot of benefits. Both have their pro's and cons. Mark

 

[RonzoTheGreat]

Hey this seems to be going well ... thanks for everyone's input ... on this last post, yes that was my original intention (volume and pressure) ... we dont have much caving up here in the NE ... so being trim in my 120 doubles isnt being compared to slipping through a tight space with LP85s (that are overfilled)

so im gathering that if i am ocean wrecking here, theres nothing to consider a "drawback" to Hps. does this sound right?

 

[Divin'Papaw]

so im gathering that if i am ocean wrecking here, theres nothing to consider a "drawback" to Hps. does this sound right?

That's certainly the way I see it. I see lots of HP tanks used by wreckers here in the Great Lakes. Certainly some LP tanks as well, but those are typically used by wreckers who are also cavers or wrecks who do their own fills.

 

[PvtStash]

I think my first tank purchase will be a Used LP steel (havent determined the size yet)

my reasons are as follows...


- If HP is all the rage I ought to be able to find a "deal" on a used LP.

- I'm about 6'3", 300lbs. , I'm Sure I'm going to need some wt. to get down, I like the idea of decentralizing my wt. setup as to "not have all my eggs in one basket", ie. have a wt. integrated BC, a wt. belt, And an LP steel tank to help distribute that potential liability.

- Being a large guy I'm not put off by the larger LP size and think I could still look well-proportioned, timmed in 110's ...(pure speculation)

- Its more likely to get a Full or more than full fill in an LP vs. an HP


Ok ... being not even certed yet this is mostly mental masturbation, but is it Sound?
Tell me where I'm wrong and what I should buy instead (and why please).

 

[Jimmer]

- Its more likely to get a Full or more than full fill in an LP vs. an HP.

I bought used Lp's, but if I was buying new I would buy Hp's of the same physical size. I bought Lp108's which are physically the same as Hp130's, same approx. length weight, etc. Now I know a lot of people get hung up on not being able to get full fills with Hp tanks, but look at it this way. If I take my Lp 108's to a shop that fills them to rated pressure, I get 108 cubic feet at 2640 PSI. If I take Hp 130's to the same place, and they cannot fill to 3500 PSI, I bet you they can still fill to 3000, since I've never seen anywhere that can't fill an aluminum 80. So I get 3000 PSI in my Hp 130's, and now I have about 117 cubic feet, so I'm still better off than I would be with my Lp108's, for the same size package.

Jim

 

[Divin'Papaw]

I bought used Lp's, but if I was buying new I would buy Hp's of the same physical size. I bought Lp108's which are physically the same as Hp130's, same approx. length weight, etc. Now I know a lot of people get hung up on not being able to get full fills with Hp tanks, but look at it this way. If I take my Lp 108's to a shop that fills them to rated pressure, I get 108 cubic feet at 2640 PSI. If I take Hp 130's to the same place, and they cannot fill to 3500 PSI, I bet you they can still fill to 3000, since I've never seen anywhere that can't fill an aluminum 80. So I get 3000 PSI in my Hp 130's, and now I have about 117 cubic feet, so I'm still better off than I would be with my Lp108's, for the same size package.

Jim

That's a point that I see so often missed. IMO the line that "you can't get a full fill with your HP tank" is missing the point. (1) You don't need a full fill to have a very nice volume of gas, (2) you can just about always count on getting at least 3000 which will give you more gas than the LP of the same dimensions assuming no overfill, (3) it's extremely rare to find a shop that will overfill a LP cylinder (outside of N Central FL) (4) you don't have to worrry about finding a place to maintain the + rating every hydro.

Now the point about finding a good deal on used LP tanks is valid and that is the one reason I fully agree with for going LP. However, if you're buying new, I'd never consider a LP.

Here's a good write-up on DiveRiteExpress that expresses the same reasoning.

 

[merxlin]

I bought used Lp's, but if I was buying new I would buy Hp's of the same physical size. I bought Lp108's which are physically the same as Hp130's, same approx. length weight, etc. Now I know a lot of people get hung up on not being able to get full fills with Hp tanks, but look at it this way. If I take my Lp 108's to a shop that fills them to rated pressure, I get 108 cubic feet at 2640 PSI. If I take Hp 130's to the same place, and they cannot fill to 3500 PSI, I bet you they can still fill to 3000, since I've never seen anywhere that can't fill an aluminum 80. So I get 3000 PSI in my Hp 130's, and now I have about 117 cubic feet, so I'm still better off than I would be with my Lp108's, for the same size package.Jim

A point I wish had been clear in my mind before I bought my LP 108. One issue I also had with the LP was the larger size and added bouyancy. I was not able to reduce the weight I was carrying as much as if I had an HP of the same weight.

 

[DA Aquamaster]

I have a surplus stewart warner compressor (with 5 HP Honda engine) and I get solid 3400 psi fills in my 3442 psi tanks. It runs fine and would easily do a full 3500 psi (where the overpressure valve opens), but I don't see the need to push it for an extra 100 psi. But if that compressor will do it, most will do it.

Where short fills seem to occur in my experience is on cascade systems with only 3000 psi cylinders rather than 4000 or 4500 psi cylinders, and on systems where the pressure to the fill whips is regulated to a maximum of 3000 to 3200 psi to prevent staff from forgetting and overfilling the normally encountered 3000 psi aluminum tanks. Some shops don't want to deal with the wear and tear of fill and storage bottle pressures over 3000-3300 psi and as a compressor owner I can relate to that.

In the grand scheme of things, 3442 psi is not very high in comparision to the normal 3200-3300 psi AL 80 fill pressure (which is usually very close to 3000 psi once it cools to room temp). Consequently, if the tech tops the 3442 psi tank off after it cools, you can still get 3200-3300 psi on the same maximum pressure used to fill the AL 80.

But again, even a 3000 psi fill in a 3442 psi tank is still more gas than a full 2640 psi fill in a low pressure tank of similar size and weight and is basically the same gas as you'd have in the same LP tank over filled to 3000 psi so are losing nothing with the "short" fill.