What size of steel tank for beginner doubles?

[DA Aquamaster]

Depends very much on where you live.

If you live in cave country, I suppose you could buy really big LP tanks and then fill them to 4000 psi and get a lot of gas. But for the rest of the world, the current range of 3442 psi tank sizes fills the bill in 95% of the cases, and when they don't you can always go the RB route.

 

[dannobee]

...And 5 years from now, the 3442 psi tank can still be filled to 3442 psi while the LP tank will be limited to only 2400 psi unless you can find a test facility that will (+) rate it again for the 10% overfill.

Or just buy your own compressor and that pressure stamped into the tank becomes your TURN pressure.

 

[PerroneFord]

Or just buy your own compressor and that pressure stamped into the tank becomes your TURN pressure.

One of my favorite quotes from my dive education here in cave country... "Turn pressure is stamped right on the tank!"

 

[PerroneFord]

If you live in cave country, I suppose you could buy really big LP tanks and then fill them to 4000 psi and get a lot of gas.

My 108s are the same size as HP130s. And I guarantee you, I leave the fill station with more gas every time. And I've never done a 4000psi fill. I know some who have, but I don't ever fill that high.
(3200psi in a 108 = 130cuft)

I have had to remind one fill operator that I was diving AL80s once! Some people just get used to letting the compressor work for a given time...

 

[DeepSeaExplorer]

If tank weight isn't an issue, which it isn't in NFL cave diving, then LP is the way to go. As for getting the plus renewed, it's not an issue for cave diving. But, these also aren't really tanks for a beginner, except for cave diving.

When not in cave country, it's hard to get a cold 3,400 PSI fill for HP tanks, at least around here anyway. But, once outside of cave country, it's not really an issue anyway.

Again, this is why the intend use is the most important factor in selecting tanks to double up.

 

[PerroneFord]

I'd disagree somewhat. The LP85 is a LOVELY tank to start with. similar in size to AL80, holds more gas, not too heavy. I'd suggest those for many divers to start with. I might get some myself to be honest.

 

[TSandM]

The great thing about the 85s is how well they trimmed out for me. They're a little heavier than Peter's 100s, but his tanks don't balance for me nearly as well.

Double Al80's balance well for me in a wetsuit, but it's because of the Jet fins. When I took them off, I did an instant headstand!

 

[DeepSeaExplorer]

I'd disagree somewhat. The LP85 is a LOVELY tank to start with. similar in size to AL80, holds more gas, not too heavy. I'd suggest those for many divers to start with. I might get some myself to be honest.

Actually, I don't think we are disagreeing. I was originally speaking of LP 104s, thus the comment about the weight, but I somehow edited that out before posting. I have worn 104s on boats where I thought the dive ladder was going to give under the weight. So they're certainly not ideal for boat diving.

85s are on the small side for cave diving, but they are a good choice otherwise. Again, I would like to know the OP intented use. If not cave diving, then 85s are great. 104s are too heavy for almost anything other than cave diving.

 

[PerroneFord]

Actually, I don't think we are disagreeing. I was originally speaking of LP 104s, thus the comment about the weight, but I somehow edited that out before posting. I have worn 104s on boats where I thought the dive ladder was going to give under the weight. So they're certainly not ideal for boat diving.

85s are on the small side for cave diving, but they are a good choice otherwise. Again, I would like to know the OP intented use. If not cave diving, then 85s are great. 104s are too heavy for almost anything other than cave diving.

You're right. I agree completely with everything you said here. Including needing to know the intended use. And no, I wouldn't want to dive 104s on a boat either. That's why I kept my Double 80s.

And if twin 85s won't get it done, I'll take a stage. Lifting and balancing these heavy 108s (old ones) is getting to be a royal pain.

 

[Craig Clark]

If you are serious about diving with doulble cylinders especially if you plan to dive with other divers using doubles then the biggest consideration is gas matching. In the world of tech diving, both divers need to have similar size cylinders so each diver has the same amount of breathable gas. If you dive with to small of cylinders you will have trouble finding other divers willing to dive with you. The same problem happens with cylinders that are to large for you. You will end up with buoyancy control problems and bad trim. The most widely excepted general use cylinder size are LP 95 steel. I would strongly recommend buying new because used you never know what they are like inside. They could have alot of rust and also they maybe close to needing hydro. The reason you want LP is because they will give you a greater volume of gas than HP cylinders. Here is the formula for comparing the difference between LP vs HP. Take 95 divided by the working pressure or 2640 psi and you will get .0359 then multiply x100 and you will get 3.59 or in other words 3.59 cubic feet of gas for every one hundred psi. If you compare a HP steel 100 with a working pressure of 3442 you will get 100 divided by 3442=.029x100=2.9 cf of gas per 100 psi. with this formula it is easy to see that the LP cylinder wins out with greater volume everytime. I hope this has been of some help to you.