OP
ScubaDan
Guest
Whoever said GUE said to over fill tanks? they don't, if fact it sounds like they are agaist it if you read what the quot say's. #1 and # 3 identifies why they would be agaist over fills.
LP, HP or aluminum
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I haven't read every post in this thread but here are a few points.
First off, I have seen more than one set of published stats on PST tanks. Specifically the catalog and the dealer price lists. The two publications do not agree. One of them (I think the catalog shows the LP 104 more pos than the HP 100 when empty, while the other publication shows the 104 more neg than the 100 when empty. I asked PST about the descrepency. they told me on was based on calculations based on design criterie (no valve) the other was measured buoyancy in salt water (including valve)
My first set of doubles were HP 100's. I based my decision on published specs. With the 100's I must add some weight (dry suit). I later switched to 104's and I need no additional weight. My wife, who is very small uses the 100's because even with her v-weight the rig is still lighter on land than my 104's. The LP 104 is 3-4 pounds more neg (empty) than the HP 100, no matter what the published data says. That figure was givven to me by PST and it proves out in the water.
First off, I have seen more than one set of published stats on PST tanks. Specifically the catalog and the dealer price lists. The two publications do not agree. One of them (I think the catalog shows the LP 104 more pos than the HP 100 when empty, while the other publication shows the 104 more neg than the 100 when empty. I asked PST about the descrepency. they told me on was based on calculations based on design criterie (no valve) the other was measured buoyancy in salt water (including valve)
My first set of doubles were HP 100's. I based my decision on published specs. With the 100's I must add some weight (dry suit). I later switched to 104's and I need no additional weight. My wife, who is very small uses the 100's because even with her v-weight the rig is still lighter on land than my 104's. The LP 104 is 3-4 pounds more neg (empty) than the HP 100, no matter what the published data says. That figure was givven to me by PST and it proves out in the water.
WYDT
Contributor
Rather than wasting our time trying to argue point to point with a wall lets look at the facts. The original question asked which tanks to buy for TECHNICAL diving.
1. LP104's have better weight characteristics for DRY SUIT diving, that is indisputable.
2. Most Technical divers wear drysuits. That point is indisputable. Yes, even in South Florida. I've worn mine in Key Largo many times. 90% of the world doen't have 80+ degree water year round.
3. LP tanks (what ever they are 104's, 95's, 85's, etc.) are better for filling Helium mixes which.... here comes a surprise... TECHNICAL divers use!
examples (totally ignoring the fact that you CAN overfill LP tanks)....
*********************
110 150
HP100 21/35 1225psi He + O2 to 1551psi + Air to 3500
LP104 21/35 924psi He + O2 to 1170psi + Air to 2640
LP 104 saves 301psi He on this mix 80psi O2 over HP100
160 200
HP 100 18/45 1575psi He + O2 to 1871psi + Air to 3500
LP 104 18/45 1188psi He + O2 to 1404psi + Air to 2640
LP 104 saves 387psi He on this mix 80psi O2 over HP100
210 250
HP 100 15/55 1925psi He + O2 to 2171psi + Air to 3500
LP 104 15/55 1452psi He + O2 to 1637psi + Air to 2640
LP 104 saves 473psi He on this mix 61psi O2 over HP100
260 400
HP 100 10/70 2450psi He + O2 to 2614psi + Air to 3500
LP 104 10/70 1848psi He + O2 to 1972psi + Air to 2640
LP 104 saves 602psi He on this mix 40psi O2 over HP100
*********************
300-600psi PER FILL savings over HP100's!!!
This difference isn't a big deal if you can go to a place that has a Haskel but many technical divers mix their own and must rely on a cascade. Helium is expensive and wasting it (as in not having the pressure left to top off a tank) is not desireable.
So, to dive HP100's with Helium and a drysuit one would have to spend more money (either buy a Haskel or pay inflated shop prices or buy more tanks for a cascade) and add more weight. Sounds like a great deal to me.
I've also heard that the HP tanks have a bad problem with rusting, especially concerning Asahi (Genesis) tanks. I can't verify that so consider it with a grain of salt.... just something I've heard from some shop owners.
Also, concerning the DIR vs not argument... it's not only DIR divers that use LP tanks. ALL the technical divers (cave and wreck/ DIR or not) I know use LP tanks.
This I promise is my last post on this subject!!
DSAO!!!
1. LP104's have better weight characteristics for DRY SUIT diving, that is indisputable.
2. Most Technical divers wear drysuits. That point is indisputable. Yes, even in South Florida. I've worn mine in Key Largo many times. 90% of the world doen't have 80+ degree water year round.
3. LP tanks (what ever they are 104's, 95's, 85's, etc.) are better for filling Helium mixes which.... here comes a surprise... TECHNICAL divers use!
examples (totally ignoring the fact that you CAN overfill LP tanks)....
*********************
110 150
HP100 21/35 1225psi He + O2 to 1551psi + Air to 3500
LP104 21/35 924psi He + O2 to 1170psi + Air to 2640
LP 104 saves 301psi He on this mix 80psi O2 over HP100
160 200
HP 100 18/45 1575psi He + O2 to 1871psi + Air to 3500
LP 104 18/45 1188psi He + O2 to 1404psi + Air to 2640
LP 104 saves 387psi He on this mix 80psi O2 over HP100
210 250
HP 100 15/55 1925psi He + O2 to 2171psi + Air to 3500
LP 104 15/55 1452psi He + O2 to 1637psi + Air to 2640
LP 104 saves 473psi He on this mix 61psi O2 over HP100
260 400
HP 100 10/70 2450psi He + O2 to 2614psi + Air to 3500
LP 104 10/70 1848psi He + O2 to 1972psi + Air to 2640
LP 104 saves 602psi He on this mix 40psi O2 over HP100
*********************
300-600psi PER FILL savings over HP100's!!!
This difference isn't a big deal if you can go to a place that has a Haskel but many technical divers mix their own and must rely on a cascade. Helium is expensive and wasting it (as in not having the pressure left to top off a tank) is not desireable.
So, to dive HP100's with Helium and a drysuit one would have to spend more money (either buy a Haskel or pay inflated shop prices or buy more tanks for a cascade) and add more weight. Sounds like a great deal to me.
I've also heard that the HP tanks have a bad problem with rusting, especially concerning Asahi (Genesis) tanks. I can't verify that so consider it with a grain of salt.... just something I've heard from some shop owners.
Also, concerning the DIR vs not argument... it's not only DIR divers that use LP tanks. ALL the technical divers (cave and wreck/ DIR or not) I know use LP tanks.
This I promise is my last post on this subject!!
DSAO!!!
ERP
Guest
OK several people in this thread have mentioned this.
What is "better weight characteristics", is it less buoyant empty, or is it to do with weight distribution or something else?
I've been considering buying HP 120's or LP 104's and this seems to be the only argument that might have some relevance to my decision.
Thanks
detroit diver
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Speaking only for myself, I am perfectly trimmed out using my LP104's and no additional weight at all. I dive an AL backplate. Anything shorter would put too much weight too high up. Anything longer and my feet sink. I'm 6 feet tall.
Hope this helps some.
Hope this helps some.
The PST LP tanks are less buoyant when empty than the HP. This is an advantage when wearing very buoyant exposure protectuion like a dry suit because most divers won't need to add weight.
IMO, using Al or HP steel doesn't solve the entire problem when diving wet because at depth you will still be overweighted. If you can't swim the rig up (possible, especially when deep and wearing a heavy wet suit) you need to ditch weight which will be a problem when you get up shallow and shoot to the surface. The dry suit has the same buoyancy regardless of depth as long as you can add and vent air. If I need exposure protection (especially for deep diving) I need a dry suit. I am, of course talking about tech rigs.
ERP
Guest
Thanks Mike, this has clarified the issue for me.
I'll be diving dry, but not doubles (it'll be a couple of years before I start thinking about tech diving) and I'd almost sold myself on the HP120's until I started wading through this thread.
If it's just 2 or 3lb's of buoyancy I'll probably end up with the HP 120's.
Thanks
OP
ScubaDan
Guest
On this Point Genesis
I just talk to a shop owner that is going to dema and he said that the DOT is going to announce that they are doing away with the LP takes. I ask him why and he said because of the over fills of the LP tank's.
Dan - You mean PST, right, not DOT?
(DOT ain't a company, its a regulatory agency!)
WYDT, I conceded (early on in this thread!) that if you're NOT going to overfill, the LP tanks would be preferrable for Trimix. Its a non-issue for Nitrox, since the amount of O2 you put in when partial pressure blending is quite small (assuming you're topping with air, of course) and the difference won't be all that material.
It WILL BE for the HE mixes...
But if you overpump the tanks, then the "advantage" goes away. And, my understanding is that this is pretty much a given when technical diving - EVERYONE overfills.
If indeed the PST LPs are MORE negative than the PST HPs, then I can see where there could be a problem with the kit diving wet. You could solve that for singles going to an AL backplate, but maybe not for doubles.
Mike, my entire point from the get-go is that the "swim it up" argument is a non-issue in that the postulated solution (ditch some weight) isn't in that is an EXTREMELY dangerous thing to do under any circumstances. A REAL solution to the (very rare) possibility of a wing failure if you can't swim the rig up (e.g. you're diving wet in a 5/7 which has a ~20lb buoyancy shift at depth) is to carry some kind of redundant lift device - a 50lb lift bag will do - for exactly this sort of emergency. Yet it is this "swim it up" issue that the DIR Zealots push the MOST when it comes to steel tanks and wetsuits!
I guess we'll have to wait and see what DEMA brings. I have no intention of buying non-hot-galvanized steels from anyone (which means PST is the only acceptable steel manufacturer right now in the US); if they disco the LP tanks then LPs are out of the game for me.
(DOT ain't a company, its a regulatory agency!)
WYDT, I conceded (early on in this thread!) that if you're NOT going to overfill, the LP tanks would be preferrable for Trimix. Its a non-issue for Nitrox, since the amount of O2 you put in when partial pressure blending is quite small (assuming you're topping with air, of course) and the difference won't be all that material.
It WILL BE for the HE mixes...
But if you overpump the tanks, then the "advantage" goes away. And, my understanding is that this is pretty much a given when technical diving - EVERYONE overfills.
If indeed the PST LPs are MORE negative than the PST HPs, then I can see where there could be a problem with the kit diving wet. You could solve that for singles going to an AL backplate, but maybe not for doubles.
Mike, my entire point from the get-go is that the "swim it up" argument is a non-issue in that the postulated solution (ditch some weight) isn't in that is an EXTREMELY dangerous thing to do under any circumstances. A REAL solution to the (very rare) possibility of a wing failure if you can't swim the rig up (e.g. you're diving wet in a 5/7 which has a ~20lb buoyancy shift at depth) is to carry some kind of redundant lift device - a 50lb lift bag will do - for exactly this sort of emergency. Yet it is this "swim it up" issue that the DIR Zealots push the MOST when it comes to steel tanks and wetsuits!
I guess we'll have to wait and see what DEMA brings. I have no intention of buying non-hot-galvanized steels from anyone (which means PST is the only acceptable steel manufacturer right now in the US); if they disco the LP tanks then LPs are out of the game for me.
A while back I posted the data on the new PST tanks which, they tell me, will be shown at dema. I would have to look for the sheet they sent me to be exact but the new tanks have buoyancy characteristics similar to the LP, they are rated for 34xx psi, I forget the DOT permit number and they will be about 14x cubic feet. I will be getting some of them
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