LP vs HP tanks on doubles...

[Sas]

Not sure if that's the case. Certainly not everywhere. I've got two sets of double HP 119's - a not uncommon configuration here in NJ. As Lynn pointed out, it's about how much gas you need and can carry easily. For my size and stature (6'2" and 175lbs) the 119's are a nice package. For my diving, it's enough gas to have full "lost deco gas" capability to do pretty much any deco necessary on back gas if I had to.

Yea here HP100s are common. Typical fill is 220bar, cave fills 250bar. I ended up going with HP100s myself because of my height (5'10"), and weight distribution (usually floaty feet), the longer tank is better. Try out a bunch of sets before committing to a new set, is my opinion but if the HP120s are working fine, stick with them perhaps?

 

[Captain12Pk]

Need more tanks for single tank dive trips, between the wife and myself. Wanted to get tanks that fill both shoes as opposed to remaining dedicated doubles tanks. At least that's the idea for now.

Alright, but if you're looking for tanks to fill both technical and recreational needs, I think you're looking in the wrong direction. Two sets may be your best option. I did something similar, I use my larger sets for different tech & training scenarios, but for teaching or "small" beach type dives I put together a set of 45's.
As long as you understand the buoyancy charachteristics of the tanks, the pressure isn't overly critical. As long as you can get HP fills as needed. In using 45's I have the added benefit of not having to have a singles reg. and a dbls. reg. set. No matter which set of tanks I use, I can grab the same regs.

 

[ianr33]

My tech instructor recomended LP because you could a much more accurate mix at low pressures. Some what important when doing things such as Hyperbolic trimix

Hyperbolic trimix ?

 

[elan]

Beware of the amount of detail below and thanks for reading through it…

I am in the process of setting up and learning doubles. Currently my setup uses two steel HP 120’s as they are the only tanks that I have in an identical pair. However for the future I am wondering about input on tanks. I get lots of input although I am not sure how much of it is totally informed vs tradition and so want to solicit more information. For intended use, I am starting tech training, and while I anticipate that most of my dives will remain recreational / light deco, I anticipate expanding to include more challenging dives and a possible move south might also include cave training, although that is still a ways off. I am physically fit but older and need to be aware of weight issues, although I can walk around on land wearing the double 120’s without much discomfort, and I can pick them up alone & put in cars or on benches ok.

Anyway, (for possible future tanks) everyone seems to favor LP steel tanks. My priorities for tank choice are less weight on land, weight underwater depending on exposure suit needed, and more air underwater. The touted LP 95’s weigh 38.7 lbs on land-empty- and buoyancy-full- underwater is negative 8.3 lbs. They need to be overfilled 10% to reach the 95 cu ft and they aren’t supposed to be overfilled after 5 years old. (Pardon to those who know all this, I’m just clarifying details.) The HP 100’s could be short filled (but usually aren’t) and weigh only 33 lbs empty on land, negative 10 lbs -full- underwater. The HP 120’s have huge gas, weigh 38 lbs empty on land and 11 lbs negative underwater. I like long and skinny tanks as for some reason I need lots of weight “forward” in order to float level.

As far as insulation and weight needed, much of the time I dive drysuit and with the necessary insulation I still need 35 lbs of weight with a steel 120, and that’s squeezed with an empty BCD at the end. (Please, it’s not an issue of a newer diver -130 dives- that is overweighted; I need only 7 lbs in salt water with an Alum 80 and a 3 mm wetsuit and hood.) Obviously if I were to get the chance to dive doubles in “warm” water say 5 mm I would need air in the BCD but otherwise most of the time the extra weight in the tank means less lead on my body.

With this info, is it just tradition that speaks so much against the HP tanks or is there some reason that I am missing? Also given that I can’t buy and unlimited number of tanks, if I were to stay with HP tanks, what are thoughts about choosing 120’s as opposed to 100’s?

Thanks for any input!

With doubles you need to factor in your height and body composition besides the other factors. I cannot trim well double HP100 with a full stage w/o putting extra 4 lbs on the tail of the tanks as they are quite short. I bought my HP100s when I had little experience and listened to people praising them. For me it turned out to be the worst set. They are short, difficult to trim and uncomfortable on the surface when for example you have to sit on the bench with them. The only advantage was their weight and volume.
HP120 are long and should give you good options trim wise if you are tall. I find that I can make AL80s, LP72s and LP85 much more stable as they require extra weight that I can place on the tail.

 

[CaveMD]

If you have a compliant shop, LP's are definitely the best choice.


The size though is entirely dependent on the person and what you wanna use them for


I use faber lp 95's with an aluminum BP and a 7mm suit. A lot of people will tell you that a dry suit is a must with doubles for redundant buoyancy etc...that's true to a point, but like i said before it depends on the person. The way mine are set up I can dump all the air out of my wing and still ascend with faber95's (i do carry a 50lb lift bag anyway) because I'm not super negative with them...not much more so than I would be with a single HP 149...but i'm also not a small guy AND i need like 20lbs to sink with a single lp 95 and SS bp...so swimming a set of lp95's is much easier for me than it would be for my dive buddy who is a 100lb girl wearing almost identical tanks lol.

 

[CaveMD]

Don't think anyone is going to overfill an LP tank by 50% in this neck of the woods. I hadn't realized they were talking about THAT much overfill. My main shop will go a few hundred over. Another shop nearby won't put it out the door above rated pressure; he calls it a "bomb". Don't burst valves tend to go off if you go too high?.... LDS said he has seen burst valves go just by getting too hot like in a car. (Adding 50 degrees F in a hot car on a 90 degree day would add slightly less than 10 percent to the pressure, by the way.) I have heard of plugging burst valves but that seems over the top to me. Anyway if that is the main reason for LP's, that you have to exceed their rated pressure by 50% to beat HP's in terms of gas/pound of tank, then my inclination is to stick with HP's, either 100 or 120. So many other more controllable risks in scuba, why add in a wild card like REALLY stressing out your tanks.

I don't think my LP 95's have ever left a pump station with less than 3000psi...Usually I like ~3400

 

[iztok]

I don't think my LP 95's have ever left a pump station with less than 3000psi...Usually I like ~3400

So instead of 2640 psi for 95 cf you pump to 3400 (almost rated pressure of HP) and get 122 cf of air in them. Which is pretty much what HP119 or HP120 gets at that pressure.

Cost aside why not use HP then? You are at the rated pressure and most of the shops will legally give you full fill on HP. Then there is a peace of mind if something goes wrong with over-pressured fill who will take responsibility for it?

To be honest, if you are going to fill LP tank to HP pressure you might as well get HP tank and get the same air in it while doing it legally. Keep in mind that even if HP is under-filled it still holds the same amount of gas as LP at the same pressure.

 

[Meng_Tze]

I don't think there is a law for or against filling scuba tanks to a specific pressure. The pressure ratings on tanks are manufacturer guaranteed tested pressures. They have to do that in order to comply with DOT regulation. Filling and using scuba tanks is unregulated by law and self-regulated by the industry as far as I know.

 

[Scared Silly]

I don't think there is a law for or against filling scuba tanks to a specific pressure. The pressure ratings on tanks are manufacturer guaranteed tested pressures. They have to do that in order to comply with DOT regulation. Filling and using scuba tanks is unregulated by law and self-regulated by the industry as far as I know.

Actually, there is a law called OSHA. A shop caught not following OHSA/DOT/CGA rules for filling will get a nice fine. OSHA rarely inspects a dive shop unless a complaint is filed.

For instance, IIRC in the last go round, it came out that customers are no longer permitted to be in the fill area of a shop while cylinders are being filled.

The pressure ratings are called the working pressure rating. Those are the pressures which the cylinder was designed for in use. Anything used in a structural manner will a have a safety factor built into it. Which means that one can go to the working limit times the safety factor and still be safe. I like to think of the safety factor as the excrement factor.

 

[Meng_Tze]

Actually, there is a law called OSHA. A shop caught not following OHSA/DOT/CGA rules for filling will get a nice fine. OSHA rarely inspects a dive shop unless a complaint is filed.

For instance, IIRC in the last go round, it came out that customers are no longer permitted to be in the fill area of a shop while cylinders are being filled.

The pressure ratings are called the working pressure rating. Those are the pressures which the cylinder was designed for in use. Anything used in a structural manner will a have a safety factor built into it. Which means that one can go to the working limit times the safety factor and still be safe. I like to think of the safety factor as the excrement factor.

Do you have a reference to the OSHA/DOT/CGA rules where it relates and states recreational SCUBA tanks and usage specifically? CGA is an association of industry manufacturers and sets standards, not laws.

A quick search of Occupational Safety and Health Administration - Home did not yield any reference to filling recreational scuba tanks. I saw a lot about commercial diving operations.