What size of steel tank for beginner doubles?

[WD8CDH]

One other advantage of the HP tanks is there is no + rating. With most LP tanks, you can only get rated capacity as long as you can mantain the + rating on the tank. When you lose the + rating, you lose 10% of your capacity.

 

[BeckyKagan]

Yikes this turned into a long thread....heres the things to look at:
1.What type of diving are you doing...cave/wreck/deep?
2.Where do you want to take your diving in the future...ie things above.

Look... im 120lbs 5'5 started cave diving 9 years ago using double LP-95's I cave dive and wreck dive, and go to mexico...If you go to mexico you rent the double 80's no problem. For anything else depends on what your doing, what your SAC rate is. See if you can rent or borrow some LP 85's or 95's or 108's to try out before you buy. If you really get into differant types of diving you'll end up with a couple sets of doubles. Personally i've done long dives, deep dives to 300ft, and never needed anything more than 95's with some stages.

Good luck with your diving, doubles are fun =) Just dive right into it in a pool or a local quarry wherevery your comfortable....Im sure you will be happy with whatever you end up with...or you could just forget doubles and go to a rebreather =)

~Becky

 

[Craig Clark]

Hey, TSand M I suggest you put your ego on the shelf for a minute and try to understand that all I was trying to do was offer some help to this person because I know how difficult it can be to find the right set of cylinders. Getting the right size for the type of diving you are doing with all the choices available can be difficult. It can be a very expensive mistake to purchase cylinders, manifold and bands only to find that they were all wrong for you. To answer your question however, I dive in the north Florida cave community and LP 95 cylinders are widely used. Second of all I don't know what your level of training and experience is but that formula you say is faulty is used for gas matching in the technical community here. If you live in a foreign country then curtain types of cylinders may not be available.

 

[TSandM]

Craig, I totally agree with you! There are lots of choices, and getting cylinders that work for the kind of diving you intend to do with them, and work for you physically, is the key.

It may well be that 95s are the most common doubles in North Florida, just as 104s may be the most common around here. I just wanted to say that what gets used VARIES from place to place, so somebody shouldn't make a tank decision based on "what's most common", unless they know it's most common for their area, and WHY.

I'll still hold, though, that just because the tank factor on HP100s is lower than the tank factor on LP95s, it doesn't mean that the HP 100s hold less gas. They hold less gas at the same pressure, but since they're rated to higher pressures, their total volume is greater. The thing is, none of this is valid in cave country, where you pick up your LP tanks with 4000 psi in them! And if the OP lives in cave country and intends to dive caves, he needs to do his tank choosing from a different perspective

 

[Walter]

if the OP lives in cave country and intends to dive caves, he needs to do his tank choosing from a different perspective

Not necessarily. Just because people will fill LP tanks to 4000 PSI doesn't mean you have to have yours filled to that pressure.

 

[DeepSeaExplorer]

Not necessarily. Just because people will fill LP tanks to 4000 PSI doesn't mean you have to have yours filled to that pressure.

Yes, but everyone does. If you don't, you'll be limiting yourself dramatically and turning a lot of dives early. I suspect, you will also find it hard to find a buddy, though I don't really know for sure because I've never ran into anyone that didn't overfill.

If I'm sitting on LP 104s with 3,600 to 3,900 and my buddy shows up with 2,640, I'm going to send him back to the dive shop to get his tanks filled. As someone else said, 2640 is turn pressure, not starting presure.

 

[texdiveguy]

If I'm sitting on LP 104s with 3,600 to 3,900 and my buddy shows up with 2,640, I'm going to send him back to the dive shop to get his tanks filled. As someone else said, 2640 is turn pressure, not starting presure.

You sound like a 'tough' cookie!

 

[Jay Roy]

Yikes this turned into a long thread....

You said it!
This thread seems to have gone way off course and gotten into a debate over cave fills, gas planning etc...The OP didnt mention anything about cave diving, deep wreck diving...
This might be his first set of double's, but won't be his last and by no means do these tanks need to follow him thru his whole diving career...Looking at his profile, it looks like he has less than 100 dives, and dives a 7 mil wetsuit...after reading everyone else's posts..I'm still putting in the plug for aluminum 80's..

 

[WD8CDH]

If the LP95 was the most common tank and it was usually overfilled to 4000psi, then I would absolutly use an HP119 instead. Exactly the same capacity at the same pressure, same carrying weight, same buoyancy, same size but greater safety due to the stronger steel. I would NOT substitute a LP95 with a HP100 because I would then have reduced capacity at the same fill pressure.

 

[DA Aquamaster]

Yes, but everyone does. If you don't, you'll be limiting yourself dramatically and turning a lot of dives early. I suspect, you will also find it hard to find a buddy, though I don't really know for sure because I've never ran into anyone that didn't overfill.

If I'm sitting on LP 104s with 3,600 to 3,900 and my buddy shows up with 2,640, I'm going to send him back to the dive shop to get his tanks filled. As someone else said, 2640 is turn pressure, not starting presure.

3900 psi in a tank with a 2400 psi service pressure is a 65.5% overfill. The hydro test pressure for that same 2400 psi tank is 4000 psi - a pressure acheived with water pressure not air pressure for safety and a pressure the tank is only intended to hold for a few seconds.

Am I the only one here who thinks that 3900 psi in a 2400 psi tank is a little insane?

Saying it is "ok" because "everyone else does it" is still a logical fallacy and does not make it any less insane.

What makes it really insane are the numbers:

PST LP 95: 8" diameter, 24.75" tall, weight=43.8 lbs, -10.4 lbs bouyant when full

96.6 cu ft @ 2640 psi (10% overfill)
131 cu ft @ 3600 psi (50% overfill)
142 cu ft @ 3900 psi (62.5% overfill)

Worthington X8-130: 8" diameter, 25.5" tall, weight=43.0 lbs, -11.7 lbs bouyant when full

130 cu ft @ 3442 psi (0% overfill)
135 cu ft @ 3600 psi (4.6% overfill)
147 cu ft @ 3900 psi (13.3% overfill)

The tanks are for all practical purposes the same size, weight and bouyancy yet the X8-130 will carry the same amount of gas at it's rated pressure as a 50% overfilled LP 95 and will carry more gas at 3900 psi while not really seriously straining it's limits to do so.

So...tell me again why would anyone still choose an LP 95 even in cave country?

It's the same story with the LP 104...

PST LP 104: 8" diameter, 26.88" tall, weight=46.4 lbs, -11.27 lbs bouyant when full

106.6 cu ft @ 2640 psi (10% overfill)
144 cu ft @ 3600 psi (50% overfill)
156 cu ft @ 3900 psi (62.5% overfill)

Faber FX-149: 8" diameter, 29.5" tall, weight=46.9 lbs, -9.4 lbs bouyant when full

149 cu ft @ 3442 psi (0% overfill)
155 cu ft @ 3600 psi (4.6% overfill)
168 cu ft @ 3900 psi (13.3% overfill)

The FX-149 weighs the same as the LP 104 and is only a couple inches taller, but holds the same amount of gas with a 4.6% over fill as the LP 104 carries when overfilled by 62.5% - and it carries 12 more cu ft when filled to the same 3900 psi fill pressure.

So again, I don't get the appeal of the LP 104, even in cave country.