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

[100days-a-year]

Heres my take from having about 300 fills done a year in a variety of Fla locations.Very few shops run banks hi enough to get a 3500 fill after it cools.A 3500 fill at the shop can often be 3100-3300 depending on how fast they fill.Most shops will fill lp tanks to 3000 without looking and they cool to 2700 to 2800 or a decent fill.Nitrox fills are often lower for some reason.I get 2900 or less in al80s a lot.Air seems to get jammed in and nitrox the take more time and are less likely to overfill.Aluminum conducts better so a 3200 hot fill often doesn't drop past 3000.The 3446 tanks sound like a good idea but like I said before a 3500 bank and a hp steel tank equal a lo fill.There are some exceptions but this is what my experience is.Having a bigger tank than you think is needed never hurt.A lot of people answer this question out of a book,real life ain't like the movies either.To properly fill a 3500 tank when your compressor cut-off is @ 3500 is just about impossible unless you top off several hours later and most shops just don't do it.BTW most compressors are rated 3000 to 3500.If it was yours and the repair bills came out of your pocket how would you fill?

 

[pdoege]

I leave my HPs overnight and get them topped when I pick them up. They are always underfilled on the boats.

If you used HPs and are going to rely on boats and recreational shops for fills then you will almost always be underfilled.

Buy the next size up.

The new E8s are in the same boat.

LPs are almost always filled to 3000 PSI and then they cool to about 2700 or so.

The HP tanks are awesome if you have your on compressor or can befriend a shop and do your own fills.

Peter

edit: Beware of really big tanks. I bought some LP120s back in the day. I never run out of air, but then again, I can do two dives on one tank. The price you pay is their exceptional weight. I now dive with HP80s. I don't have nearly the air reserve, but for recreational dives the convenience makes up for it. They are chronically underfilled, so I actually get in the water with about 72 cf. My air consumption is good enough to make that a non-issue. You may want HP100s or LP80s. Both are probably better choices than the bigger LPs or HPs. Your consumption may vary

 

[drbill]

I use HP steel exclusively. Before my HP120 failed hydro, I easily got two good dives (50-70 min depending on depth) or three shorter (35-40 min) dives on it. Given the number of dives I do a year, it cuts the cost at least in half! It also gives me the option of doing a good deco dive or a very long shallow dive.

Dr. Bill

 

[peterw]

Thanks for all the feedback. I've decided to go with the PST E8-130 . Actually I bought an E8-130 tonight. Dive N' Surf in Redondo Beach has the E8-130 in stock. The PST E8-130 comes with a DIN/K valve (the valve works with yoke or DIN, unscrew the insert to use with DIN). The E8-130 is in line with all the 120s but is smaller and lighter. I lined up the full line of PST tanks along with other tanks in the dive shop tonight and the PST tanks are just great. The PST tanks are smaller and lighter than all other tanks with similar capacities.

Actually the E8-120 used to be called LP-104 however since the tank can handle higher pressures the result is greater capacity.

The capacity of the E8-130 is as follows:

130 cf at 3442 psi
119 cf at 3000 psi
106 cf at 2640psi

PST E8-130
Pressure rating: 3442 psi
Inches in Diameter: 8
Inches in Length: 25.56
Weight Empty: 42.2
Buoyancy Full: -14.6
Buoyancy Empty: -4.8
Price: $329

 

[peterw]

I liked the E8-130 I got the other day so much I went back and traded in my two AL80s for a discount on another E8-130. Now I have a nice new pair. I'm so happy!

 

[bertschb]

re: the E8-130

According to the PST web site, the boyancy when empty is -1.8 and it's -11.55 when full. Not the -4.8 and -14.6 listed above.

Did I read the PST web site charts wrong?????

 

[LUBOLD8431]

bertschb once bubbled...
re: the E8-130

According to the PST web site, the boyancy when empty is -1.8 and it's -11.55 when full. Not the -4.8 and -14.6 listed above.

Did I read the PST web site charts wrong?????

The -4.8 is for the old LP 104's.

Good choice on cylinders, BTW Peter...

IMNSHO, Pressed Steel makes the best steel cylinders in the world for alot of reasons, but most importantly because they are GALVANIZED...

 

[Jeddah Aquanaut]

I love using Poseidon HP tanks. Not that I've ever had an o-ring blow on any LP tanks, but there is definitely no way that will happen here. Two weeks ago I was using Poseidon for the map making part of the DM course. While still staying within limits, I got 94 minutes out of it, with a good amount to spare (I'd have to go downstairs and look).

Another plus for me is that, with my skin suit, I need 0 pounds of weight with the HP steel tanks. I have been taking a couple of clip-ons anyway for the OW students that my instructor brings along.

4500psi is nice, but not vital. Usually I use steel LP 80's, as not many of my buddies also have HP. You can only stay down as long as the biggest air hog anyway. They also cost more to fill. It all depends on what diving one wants to do.

Oh, for all of those who are starting to feel the chill of winter approaching, I feel your pain. Yesterday it was 30 degrees on the surface. Terrible, unbearable, undeniably horrific in its intensity. I wouldn't wish it on my worst arctic enemy.......
OHHH, I forgot to mention, I meant 30 Celsius.

 

[NAM001]

peterw


i ahve faber lp 95's. i have had no problem with them being over filld. i have had them filled to 3300 hot/3000 cool. i am told the burst disk is at min 3500. these same tanks are charged to 3500-4k for the cavers. i dont know if i would try 4k on mine but 3k is routine for me. i recently got 1 hour at 70'+/- and returned with 800. there is nothing like extra air if you or someone needs it. the tank comes with a combo yolk/din valve 40# weight range. one thing about the larger tanks. you dont need twice the tank to get twice the time since you are coming up at 1k on say an 80. that would make about 55cu ft used for the dive and 25 left when you return to the boat. with the say a 108 such as i have when filled to 3k i have 25 cu ft air at the boat and the other 83 or so is used for the dive. a 120 tank would nearly double the down time of the 80 cu ft. makes that boat fee a bit easier to swallow. first in last out every one is happy and you get 2 one hour dives for thier 2 30-40 min dives. keep it with in the tables and its a great deal. the tanks were expensive about 250 each. but they will last for years. btw i dont suggest routinely filling to hp. its a wast to fill to hp and then come from a shore dive with 1500 when you can fill to ratings and reduce tank stress. the tanks can handle it. fortunately perhaps its hard to find someone who has the capability to fill above 3300. THAT I BELIEVE IS A GOOD THING for the fate temters. for me the bouyancy issues of the larger tanks became an issue. i there fore bought 2 faber lp 95's instead of a 120 or 130. hope some of this is usefull to you. btw i have found that shops are more open to your fill requests when you are oacking steel and the lp's are in the charging capability of everyone.

regards

kws

 

[Teufel-Hundin]

We have been lobbying with a few tank manufacturers for years on the LP tanks. They are hydro at 4000psi and are supposed to be made to a standard of around 10000 fills at that pressure with a --BURST-- pressure over 6000psi. These are the same standards that most HP tanks are tested at and are expected to meet. So our question has been if the manufacturer makes both the LP and the HP have the same usage rating and burst pressure why designate LP tanks as 2400-2700psi fill tanks. There answer was that the LP tanks are for people whom want to be easier on their gear with the lower PSI and still get a high quantity of air,but the DOT standards make them keep the tanks within the same range "standard"as the HP. So we have been putting Hp rated Din valves on LP tanks and filling to 3500psi for years. We have had a number of our tanks repeatedly Hydro, Vis, and Eddy checked by the manufacturer and have found no excessive wear. This gives us the ability to fill the LP like a HP for ALOT more air. This REVALATION is how the manufacturers are now offering their old 108 at the NEW 130 size no different tank just a new HP Din valve and a new rating. BTW the new OMS LP 130 at 3500psi gives ALOT of great downtime.
I would also not recommend doing this with ANY unknown or very old tank. Get newer LP make sure they are checked ahead of time and take care to keep them dry on the inside as the higher the pressure the more oxidation you get.
PPS. THIS IS ONLY FOR LPSTEEL TANKS DOES NOT APPLY TO ANY ALUMINUM TANKS!!!!!