Older steel LP72s for sidemount?

[vicp]

I just got a PST (steel) LP72 (DOT-3AA-2250 - born 1981) and tried sidemounting it (along with an AL80) in the pool. Filled to ~2200 it just would not ride right. No side to side roll versus the 80 on the other side but the 72 would roll up like it was tail light. Swam around for a while trying different rear attachments. When I took the 72 off with about 1600 psi it stood straight up on its valve on the bottom. The AL80 with 2500 lay flat on the bottom. This is much worse than my Faber LP85s that just start to get tail light at about 1600 psi.

I have read that these are great sidemounting tanks, but this one is too "floaty" in the back. Is it just this particular PST 72 or all they all the same? Are the somewhat newer 2400 psi steel LP72s any better?

Was hoping to pick up some cheaper, lighter, lower capacity sidemount tanks (read that the older steel 72s would do it) but this one is not that good. Those of you that sidemount these older 72s, is this typical, do you use weights on the rear or just attach the middle/rear of the tank to a waist D-ring (or what)?

[Slüdge]

I know this is confusing, but Pressed Steel only used the designation "LP" for 2400psi cylinders, not for 2250psi cylinders. I'm not sure they ever had a 2400 72, but I believe Faber did.

Also keep in mind that the first stage you use has a lot to do with how tail-light it is. (I have a bunch of aluminum Mark 20s that make stages ride way better than brass.) The less brass (mass) in the first stage, the lighter.

[DA Aquamaster]

Steel 72s were made by several companies over a period of about 30 years so you'll encounter a lot of variation, even within the same make of steel 72 over time, and some can be pretty floaty when near empty.

In general I think steel 72s tend to get light in the tail at low pressures, but I don't really notice this until they get under 700-800 psi, and that's not normally an issue in a cave. That might be due to how I rig mine, the Mk 17 regs I use, etc but for me it's not a noticeable problem until the pressure is low enough that I need to be out of the cave anyway. They are better in that regard than AL 80s where I do notice the floaty tail at 1200 psi or so.

IIRC, Faber made a 75.8 cu ft tank that was basically a steel 72 with slightly thicker walls and a 2400 psi service pressure. I always wanted to get some but never had the scratch at the time (late 80's - mid 1990s).

[vicp]

Not sure if this tank is "designated as an LP72" (I simply called it that) but it is a steel 72, original hydro in 1981, has what looks like a flag or a "P" with a large upper loop and what looks like a small "s" underneath (can't see a "t"). The hydro man thought it was a PST. It is 6.9" in diameter and between 25" and 26" tall to base of valve and has a serial number 9676Y. With a HOG D1 first stage it felt tail light when full and with ~1500 psi stood straight up from the valve on the pool bottom. I will refill it again and toss it in the pool and see how bad it is.

An issue, BTW, that I had with Faber LP85s, when I got them real low (~500 psi) was that tails come up to different heights between the two tanks. They had their boots on and when I removed the boots they were even. Apparently the Faber boots can trap some air in them. I now use boots to store steel tanks upright or to work on them but take them off when I dive. The boot on the 72 is fairly open on the bottom, so I doubt that it traps any air but will take it off when I try it again.

So some of the older steel 72s are "floaty" while others are not. I thought that the 3AA-2250 were fairly generic with not much variation between manufacturers.

[DA Aquamaster]

Steel 72s are all the same in much the same way that low pressure 95s are all the same. PST, Worthington, Coyne and Faber 95s all have some differences and while PST and Worthington have similar buoyancy traits the other two are distinctly different.

Another example are AL 80s. Luxfer 80s and Catalina S80s are similar, Catalina C80s are the slightly shorter and more negative, Walter Kidde 80s had thicker necks and floated differently, and Norris and Kaiser Aluminum AL 80s had minor differences as well.

In back mount, divers were aware of buoyancy differences but few really noticed the trim differences between tanks of similar size and capacity - other than perhaps trim issues in doubles when switching between sets that were markedly different, where in side mount any tail light tendency is very apparent.

[vicp]

Thanks for the responses - the tank is not as bad as I first thought.

Filled it up, took the boot off and went back into the pool. It rode a lot better - not sure why (boot?). At about 1300 psi, I settled to the bottom of the pool, unclipped the tank and held it in front of me, by the knob and by the first stage. Breathing it down, the tail started to come off the bottom at about 1000 when held by the knob and around 900 when held by the first stage. I was surprised by the difference this really short distance in (lever) arm length made. Anyway, I can live with this.

Heck - the tank cost me $20 from a shop (it was somewhere in the back not being used) and the hydro cost me $15 (it passed easily). I cleaned it myself with a homemade whip, simple green and hot water and dried with a tube attached to a hair dryer. A hell of a deal for $35.

I think I may try to pick up a few more of these. Maybe even double up a pair to backmount again - sacrilege! I did swear off backmount at the first taste of sidemount (at least I will never backmount double 108s ever again (ugh!) or 95s (too head heavy) but I did save a couple of manifolds and a set of 6.9/7.0 inch bands just in case I ever wanted to bakmount double 85s again. Might use this for a pair of 72s.

[aquaregia]

My Walter Kidde 72 is silly floatie by comparison to my Norris and PST setups. I like my backmounted 72s, I think they run around 65lbs a pair.

[Aktun]

. I'm not sure they ever had a 2400 72, .

r.

Not a 2400 but they had a 72 at 2475

[vicp]

Not a 2400 but they had a 72 at 2475

The 2475 is the 10% overfill ( "+" hydro rating) on a 2250

[Diverlee]

I use the old 72's. They do float light. I put a 2 pound wt on the tail or cam band of each one. That solved the problem