Buying a tank, if you don't know what you're buying

[tech3324]

...but the way I see it is that no water can possibly enter if there is compressed air in it.

That's the way I see it too. I'm back from a boat dive with 200psi in an LP80 and it will sit for awhile. Has never been a problem and haven't had to tumble a steel tank yet.

 

[teknitroxdiver]

Logic (and physics) tells us that if there's even 1 psi over ambient, no water or anything else could enter the tank.

 

[Birddog1911]

I got lucky, and just bought 2 AL80s, dated 94, for $20. My shop is doing the hydro/visual and fill. If they fail, no charge to me.

 

[guruboy]

That's a really good price on the tanks. How much are you going to pay for the hydro+vip though?

 

[Brandon]

Logic (and physics) tells us that if there's even 1 psi over ambient, no water or anything else could enter the tank.

Heretic! This is life support equipment. Would you trust your life to science?



Cylinders out of hydro/vis have not been maintained by their owners. I start at $25 and explain how easily (especially at local prices) it is for their used cylinder to cost every bit as much as a new one by time it's brought back up to serviceable condition.

One of our local shops actually went around and bought all the cylinders sitting in people's garages and refurbished them. Wasn't a bad plan and put a lot of used cylinders back on the market at fair prices.

 

[TrimixToo]

I have about 40 tanks, not counting bank tanks and such. A few observations...

First, there is nothing wrong with steel tanks. I've bought all the ones I have now used. The biggest pain is keeping the painted ones from rusting on the outside. After hydro they need to be tumbled to get rid of the flash rust, but to be O2 clean they need to be tumbled anyway, as do aluminum tanks. They DO NOT rust between hydros if the compressor they are filled from has decent filters (meaning dry air) and a rust inhibitor is used after O2 cleaning. If you dive in salt water, galvanized LP or non special permit (SP) HP tanks are the way to go, because you won't be keeping after the paint over the years. Galvanized SP HP tanks have a perhaps-deserved reputation for failing the 2nd or 3rd hydro. Also, their SPs must be renewed by the manufacturer, and some leave owners in temporary situations where the tank cannot be requalified by the hydrotest facility. Personally, all my steel tanks are 3AA tanks and no SP tanks. Oh, one more thing about steel. Do NOT buy lined tanks, or vinyl-clad tanks.

Aluminum tanks made of the alloy thought susceptible to sustained load cracking (SLC) have SP numbers rather than 3AL numbers, which makes them easy to spot. It's not 100% clear that the problems are significant, since they can be requalified with a 3AL overstamp if they pass but I retired two rather than take the risk.

I have never bought a tank that did not include a valve that was installed and closed. Most of the ones I have bought have been out of hyrdo (some by decades!), and none have failed. Some are old enough to have ICC numbers rather than DOT numbers. To me, buying a used tank is very low risk. Local hyrdros are $25, and I tumble and clean the tanks myself. YMMV, of course.

The LP85s, if that's what you got, are a fine choice. A little bigger than AL80s, good profile, a bit long for short people but fine for most of us, with good buoyancy characteristics. I wish I had a few more of them myself!

John

 

[guruboy]

The LP85 I have are smaller than AL80

 

[TrimixToo]

The LP85 I have are smaller than AL80

I meant capacity, not external dimensions, actually, and I should have been clearer. Great reference here: http://www.indianvalleyscuba.com/se...ction/information/CYLINDER SPECIFICATIONS.pdf

John

 

[NAM001]

Hello Peter

Most used cylinders for sale are out of hydro and have been sitting for years. The exception would be the active diver who has moved to a different type of cylinder or switched to a rebreather.

I've bought maybe 30 used cylinders. All but one were steel. I've had 3 of them fail hydro, and they were all in a batch I bought at once that had been sitting outside for several years without air in them. One of the ones that failed had filled halfway with rainwater. One of the ones that passed had filled halfway with rainwater. Cylinders are tough and while hydro failures do happen, they are rare.

For AL80s, check the date. Anything made before 1990 is, at best, more trouble than it's worth, because of known problems with the alloy used back then:

Is my cylinder made from the "bad" alloy aka AL6351?

Steel cylinders of any era are still good, provided they pass, but know what you're buying as there are some older/oddball cylinders out there that aren't especially useful for diving either because of insufficient capacity or because of buoyancy problems.

Ask what is included in a hydro test. Most scuba shops send their hydro work out but also include a VIP sticker, neck o-ring, face o-ring, and air fill in the price. Some will perform valve maintenance if necessary. Some will replace the burst disk. I usually disassemble the valves on the cylinders I buy, clean them, and replace all the o-rings and the burst disc.

2air.... just one comment about the older tanks and 6351 alloy. I am not a big fan of luxfer. not because of my concern but of others. Luxfer had problems with the 6351 only one year when they got a supply of tank material from a source. All the other years were OK. I think they were the only ones that used that alloy. the 606x being used today has had no problems and older tanks should be ok with out question as long as the hydro and vis is good. Too many shops use a blanket rule. Older than 20 yr's = no fill. which is pretty unfair to the remaining good 99% in the field or pond as it may be.

 

[NAM001]

Thanks for the replies. I've read through a bunch of reviews of pros cons of aluminum/steel and various tank sizes but am not sure what would be best for me. Here's my situation:

• I've only ever dived AL80s. The buoyancy issues people cite for aluminum tanks haven't bothered me.
• I have always ended dives because I run out of air instead of bottom time
• I'd like to do this on a budget, but if a better solution is a bit more money, that's ok
• I'm not currently Nitrox certified but intend to get certified

What kind of tank (or tanks) would you recommend I buy?

There are two LP85 Faber steel tanks with plus rating for sale in my area, with inspections through 2018 and 2019. $300 for the pair, with offers accepted. Would these be a decent option, and what's a reasonable price?

GRAB THEM if and only if you are using weight to stay down. your buoyancy will shift about 4-5# in the neg when you go to steel.
Also tha al80 is 77 cuft. the lp85 is 85. when you start doing things like rock bottom calc's you will be glad you have the extra 8 cubes. Quite often shops do not look at the tank and you get 3k fills on the lp85 and you end up with a good fill when cooled or up to about 95 cuft at 3k. If you are not using weight and you use these tanks you are asking for problems unless you get some more suit to off set the neg buoyancy. The issue of dumping lead for the tank moves the weight up to the center of the3 chest and not the hips. It however removes about 5# of weight that was once ditchable. Make sure you look at all the angles before you buy. Still 300 for the pair is a good deal. They will last you for years with minimum care. Oh and one more ting the lp85as are very close to the same height and weight as the al s80's.