LP vs HP?

[Puffer Fish]

Thanks in_cavediver, that is the point I was trying to make. If I can only get a 2450-2600psi fill, then an LP makes more sense, as it would have more c.f at that PSI. Now I have to do the math for larger capacity HP tanks, in the event I get off this boat and can get a higher PSI fill. Then they will make sense (if the numbers work out).

A worthington LP 85 weighs a nice 34 lbs, a worthing hp weighs 33 lbs..(advantage HP). A 90% fill on a LP = 76.5 cubic ft. A 69.8% fill = 70 cubic feet (roughly). So there is around a 9% advantage to LP, but you could get a HP 120, which would have more air than either. Yes, it would weigh a couple of pounds more, but even at 2450, would have a lot more air...

Obviously, the big issue is cost.

 

[SparticleBrane]

Correct me if I am wrong, but don't HP tanks have thicker walls (and thus smaller actual volume) than the LP tanks. Isn't that why they can handle the higher pressure?

Flat

Incorrect, at least with Faber tanks. Not sure about the thickness of the walls but the FX and LP series have the same internal volume for the 'corresponding' size tanks. (117 & 95, 133 * 108, etc).

 

[in_cavediver]

A worthington LP 85 weighs a nice 34 lbs, a worthing hp weighs 33 lbs..(advantage HP). A 90% fill on a LP = 76.5 cubic ft. A 69.8% fill = 70 cubic feet (roughly). So there is around a 9% advantage to LP, but you could get a HP 120, which would have more air than either. Yes, it would weigh a couple of pounds more, but even at 2450, would have a lot more air...

Obviously, the big issue is cost.

Actually, there is a big difference in the tanks themselves. I had a HP120 a couple years ago. It was a VERY tall tank and I never did get that comfortable wearing it. The 85's/100's are quite a bit shorter. I'm 5'11"ish and the 120's, while divable, weren't comfortable.

For me, the choice would be between the LP85/HP100 and the LP104/HP130. Similar heights but 7.25" vs 8" diameters. Wieghts, the 104's if memory serves are about 10lbs heavier out of the water. (I'd check that for current tanks before taking it as fact)

 

[Skeeter1097]

I have Worthington lp 108's, I think they are the best. I had hp 100's but a fell was a fell 100 of 108 heave at 3500. lp 108 at 2400 but most all lds I go to well fell to 3200 cold that is about 140scf or so. In the keys and two lds I have goon 3700. That works for me. Two dives a tank a 108 at 3000 would put most divers including me in deco for shore.

 

[NJMike]

I thought PST went out of business? Their website is still up, so maybe my info is wrong.

I have a question...do charter boats carry compressors and refill the tanks between dives? If the answer is 'yes', is the follow up question about whether or not the majority can fill tanks to higher pressures? For instance, if I get an HP 100 (I'm looking), will most boats not be able to fill to 3442 psi?

 

[Warren_L]

OK, I could be dense, but if I get a 2450 psi fill in an LP 100, I'll have 92 cf of gas. If I get the same 2450 psi in an HP 100, I'll only have 81 cf of gas. I think that makes logical sense, don't you?

This is why the imperial system is so screwed up. If you're comparing a LP100 with an HP100, of course, the LP100 will have more gas in it at the same pressure. If you look at the internal volume of the tanks (as they are rated in the metric system), they are very different, so the LP100 should be significantly bigger in size than an HP100. A LP100 will have similar internal volume (sometimes referred to as water volume) as an HP130, so comparing these two would be more relevant. They may not be exactly the same, so there, of course, may be differences in the actual weight and dimensions of the tanks, which would be more of an issue with weighting and trim, but that aside, if you're only looking at this from a volume/pressure perspective, an HP tank versus an LP tank with the same internal volume (water volume), the HP tank is always more advantageous than the LP tank as you have the ability to legally fill to higher pressure. If, in this case, you can only short fill the HP tank to the rated pressure of the LP tank, you have the same volume of gas as a properly filled LP tank.

The only disadvantage I can think of is that if the HP tank may be more expensive, and if you never have the opportunity to fill the tank beyond the rated pressure of the LP tank (and I mean NEVER), and the LP tank is cheaper, then yes, it would be a waste. And of course, weight and trim may be an issue, but relation to the original concern, this has no bearing.

 

[Leadking]

I have LP 108's, and I believe they are 108 at 2640, not 2400. But I've been wrong before....shocking as it may seem.

All 3AA tanks that are manufactured are marketed with the capaciity of the overfill included in the CF calculation. See http://www.seapearls.com/dealerarea/public/SeaPearlsCatalog.pdf for Worthingtons specifications (page 2-3)

 

[merxlin]

A worthington LP 85 weighs a nice 34 lbs, a worthing hp weighs 33 lbs..(advantage HP). A 90% fill on a LP = 76.5 cubic ft. A 69.8% fill = 70 cubic feet (roughly). So there is around a 9% advantage to LP, but you could get a HP 120, which would have more air than either. Yes, it would weigh a couple of pounds more, but even at 2450, would have a lot more air...

Obviously, the big issue is cost.

Here is what I found:

LP 108 - 8" diam x 26" hgt, 41 lbs, -1lb (empty) - 8lbs (full) , 100 c.f. @ 2450 PSI
HP 120- 7.25" diam x 29" hgt, 48 lbs, -7 lbs (empty) - 16lbs (full), 84 c.f @ 2450 PSI
HP 100- 7.25" diam x 24", 38.7 lbs, - -7 lbs (empty) - 15 lbs (full), 72 c.f. @ 2450 psi

Again, I am using 2450 because that is the typical fill on the dive boat I use very frequently.

 

[Hoosier]

Here is what I found:

LP 108 - 8" diam x 26" hgt, 41 lbs, -1lb (empty) - 8lbs (full) , 100 c.f. @ 2450 PSI
HP 120 - 7.25" diam x 29" hgt, 48 lbs, -7 lbs (empty) -16lbs (full), 84 c.f @ 2450 PSI
HP 100 - 7.25" diam x 24", 38.7 lbs, -7 lbs (empty) -15 lbs (full), 72 c.f. @ 2450 psi

Again, I am using 2450 because that is the typical fill on the dive boat I use very frequently.

I think you quoted a wrong tank. HP tanks we are talking about here is 3442 psi rated one, not 3180 psi + 10% one.
Worthington L8-108 2400 +10% 108CF 8inch Pwdr 26" 43lb neutral ~ -8lb.

Faber LP-108 2400 +10% 108CF 8" Triple 26" 41LB -1lb ~ -8lb

Worthington LP8-95 2400 + 10% 95CF 8" Pwdr 23.7" 38lb -1lb ~ -8lb

Worthington X7-100 3442 100CF 7.25" Galv 24" 33lb -2.5lb~-10lb

Worthington X7-120 3442 120CF 7.25" Galv 28" 38lb -2lb~-11lb

 

[limeyx]

OK, I could be dense, but if I get a 2450 psi fill in an LP 100, I'll have 92 cf of gas. If I get the same 2450 psi in an HP 100, I'll only have 81 cf of gas. I think that makes logical sense, don't you?

because the tanks are different sizes.

My point is, that you could get (say) an HP-120 that's the same physical size as the LP-100. Many people say they'd rather take an LP-100 instead of the HP-120 (using our example) because they can get a "full" fill, which does not make sense.