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Questions about LP72 tanks

Discussion in 'Tanks, Valves and Bands' started by elgoog, Aug 25, 2015.

  1. elgoog

    elgoog DIR Practitioner

    # of Dives: 200 - 499
    Location: San Francisco Bay area
    Hi -

    I'm looking to get a couple of LP72s for wifebuddy - the lower weight will be much appreciated by her for our shore dives. Her air consumption is significantly better than mine and her on this tank with me on something in the 80-100 range works perfectly for the dives we do. I've seen a lot of posts here about them and some specific recommendations what to look for but I had some additional questions.
    - Galvanized finish instead of painted seems to be the preference. What's the reason for this? Is this as simple as "if it looks galvanized, it is galvanized" or are there tanks which are galvanized but painted over? Any way to correctly identify them?
    - Tanks with linings are bad (?). Any way to find this out from tank markings? My LDS does VIP before sending it off for hydro anyway, so they would confirm if this is a problem or not.
    - Assuming the tank passes hydro+VIP, any reason using banked EAN32 would be unsafe, maybe due to any lining?

    Thanks in advance,
  2. tbone1004

    tbone1004 Technical Instructor ScubaBoard Supporter

    # of Dives: I'm a Fish!
    Location: Greenville, South Carolina, United States
    big thing first, your tanks are backwards if you are diving as a buddy team. Your wifebuddy needs to bring enough reserve gas for your Hoover self to get up and out, so make sure you're doing appropriate rock bottom calculations.

    Galvanized, if it's PST it is hot dip galvanized, more durable finish than painted galvanizing *like Faber*.
    Linings are bad, not sure if you can tell this from any markings, but it's obvious with an inspection light with the valve off.

    No reason banked EAN32 isn't OK, get the tanks tumbled or sand blasted if they need it, hydro shops will sometimes be able to do this for you to make sure they're clean, but no need to O2 clean.
    decompression likes this.
  3. dumpsterDiver

    dumpsterDiver Banned

    # of Dives: 2,500 - 4,999
    A long time ago, my wife used to use one of those tanks and she could dive longer than I could on a 100 cu-ft tank... and I used to get 1.75 hr dives in really shallow water.

    Those old steels are what 30 or 40 years old? If it looks galvanized it is. If it is not all bubbled and rusted on the outside by now, it is probably not gonna start rusting terribly. check carefully under the boot if you are looking to buy old steel tanks.

    Of bigger concern is the inside. They need to be pretty clean or you have an expensive tumbling. In my experience, they are great tanks.. light weight, smaller diameter, shorter than an 80, heavier in the water (just a little)... they are GREAT tanks,, if they provide enough capacity for your needs..
  4. KWS

    KWS ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: SE TEXAS
    Good questions and good answers to boot. I would suspect that you should not have to worry about rock bottom issues as the lp72's are 2250 psi with additional 10% if qualified. The al 80's only have 77 in them. so an lp72 +10% is greater than 77. If your wife has great sac then you have plenty of air in her tank to get you both up. I would always keep track of air consumption from the half psi point of your tanks and not spend a lot of time below 70-80 ft to maximize bottom time. coated tanks. one look in a tank and you will know if it has a coating from that era. many like galvanized tanks because of painted tanks ability for water to work its way between the paint and actual tank and rust through he tank un-noticed.. I have never had problems with this however 72's are old tanks and have had decades to develop problems. A good hydro and vis should put your mind to rest. AS hydro's go find one that will do a +10% cert on the tank if you can. The inside lining is that same concern as a painted tank only more so as tehPPO2 is higher and corrosion is sped up. I would not take any tank with a coating on the inside other than an anticorrosion coating that is thn enough to scratch through. faber has a whitish painted on coating in their tanks inside for this purpose. If the tank passes its testing and inspection ter is no restriction to nitrox. There are O2 cleaning procedures and I would have it done as you don't personally know what has been in the tank. Nothing I know of on the tank markings is associated with the tank being coated or not. for just a couple more #s you can put her in an lp85.

  5. spectrum

    spectrum Dive Bum Wannabe ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: The Atlantic Northeast (Maine)
    A low pressure cylinder only attains the stated capacity when it has the + rating. Lacking the + it is more like 65CF when filled to the stamped service pressure. Be sure to explicitly specify that they calculate for the + endorsement, it is seldom offered automatically.

    I will reiterate to look under the boot. Most of these are prior to self draining boots. Old boots were often rubber clinging socks that harbored salt and were very slow to dry.

    Hot dipped galvanized is highly desirable, especially for ocean use.
    If they are hot dipped galvanized be sure the hydro facility performs the rounding procedure prior to hydro.

    Avoid anything that does not have a modern full size valve thread (3/4" NPS) , least desirable are the little 1/2 tapered thread valves.

    LeadTurn_SD and dumpsterDiver like this.
  6. kwinter

    kwinter Rebreather Pilot

    # of Dives: 500 - 999
    Location: South Jersey
    This is grossly inaccurate. A low pressure cylinder attains whatever capacity it is filled to, regardless of rating. Take a LP cylinder to cave country and you can probably get it filled to 4000 psi if you like. It all depends on the shop, or if you fill it yourself.
  7. dumpsterDiver

    dumpsterDiver Banned

    # of Dives: 2,500 - 4,999

    LOL.. take a 71.2 to cave county and ask for 4,000 psi.... see how that works for you. :shakehead::shakehead::shakehead:
  8. lowviz

    lowviz Solo Diver ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Northern Delaware or the New Jersey Turnpike
    72cuft - 10% = 64.8 cuft @ 2250.

    64.8 x (3000/2250) = 86.4 cuft.

    I can get a 3K fill on any current steel 72, not a penny more...
  9. DA Aquamaster

    DA Aquamaster Directional Toast ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: NC
    A few thoughts:

    1. Steel 72s nominally hold 71.2 cu ft at 2475 psi. At 2250 psi they hold 64.7 cu ft.

    2. They are 3AA steel tanks just like 2400 psi LP tanks (which were also marketed with the capacity at the 10% overfill pressure). An LP 95 holds 95.1 cu ft at 2640 psi and 86.4 cu ft at 2400 psi. The difference between the 2250 and 2400 psi 3AA tanks is the slightly thinner wall thickness for the lower pressure 2250 psi tanks. Cave country dive shops commonly fill 2400 psi steel tanks to between 3600 and 4000 psi. Given that the hydro test pressure is 3600 psi, I'm fine with a 3600 psi fill and am generally less pleased with 4000 psi. Jus'sayin.

    3. A comparable "cave fill" for a steel 72 is 3,375 psi, but you won't generally get that as people cite the age of steel 72s and seem to have a misunderstanding of what age means for a steel tank. The irony is that there are steel 95s older than the youngest steel 72s, and age itself is irrelevant.

    We used to see steel welding tanks come in for hydro that were made prior to WWI, were plus rated during WWII and still qualify for a plus rating today. It's the condition of a 3AA steel tank that matters, not the age.

    4. Provided the fatigue limit is not exceeded, you can theoretically put and endless number of cycles on a steel tank, and the 3AA engineering standard was generous enough to ensure the fatigue limit was not met even at test pressure. Now...going over the test pressure is something else and the potential does exist to exceed the fatigue limit, which will start limiting the number of cycles that can be done before the tank will fail a hydro test - thus I prefer to keep my fills to 3600 psi on a 2400 psi 3AA steel tank.

    5. In any event, I routinely fill my steel 72s to 3000 psi, where they hold 86 cu ft of gas, and that's still comfortably under the hydro test pressure.

    6. Some steel 72s were ungalvanized and painted. Others were galvanized and then painted, still others were just galvanized and left with that finish. US Divers sold them in all three configurations and also sold them dipped in plastic.

    Plastic coating was one of those things that seemed like a great idea at the time. However once the coating got a hole in it or started to delaminate, it would let water under the coating and hold it next to the steel, causing rust and eventually pitting that would cause the tank to be condemned. In order to properly VIP a tank, the coating has to be removed. Doing that requires paint stripper and a fair amount of elbow grease to scrape it off.

    The same applies for any bubbled paint or any stickers that are not 100% intact or that show any roughness under the sticker.

    Tank boots can cause the same problem with rust if they are not ribbed to ensure all the water drains from under the boot. Those snug fitting smooth tank boots have killed more steel tanks than any other factor.

    7. If you buy a steel tank, pull the boot and inspect carefully under it. Rust, pitting or bubbled up paint are all solid reasons to pass on the tank.

    8. Internal tank liners were very popular in their day, but they had the same potential problem as the plastic outer coating - once compromised it would trap moisture under the liner, cause rust, and also prevent proper inspection. A few companies still use a liner in some steel tanks, but the material is white and shows any discoloration from rust. The old liners were tank or brown and were not VIP friendly. If you have a tank with the old liner in it, it will have to be removed. That will take about a week's worth of tumbling with an aggressive media as the liners are tough to remove.

    9. A lot of companies made steel 72s and how they mad them changed often changed over time, and thus they are not all created equal. I have some that get light in the tail when empty while others maintain a normal trim. Some are also buoyant when empty while others are still a pound or so negative. If you're going to use them as doubles or for sidemount diving, find a pair that are well matched.
  10. Bob DBF

    Bob DBF Solo Diver

    # of Dives: I just don't log dives
    Location: NorCal
    As dumpster diver pointed out, a 72 is actually 71.2 cuft at 2475#, so much for truth in advertising. The AL80 is 77.4 or 78.2 cuft at 3000#, depending on the tank, which shows that people love round numbers, especially if they round up.

    I get fills between 2500 and 2800# regularly without the + stamp. I use them on a quick dive, dives where a larger tank would have me freezing, or as old school doubles where I want a tank larger than my 120.

    dead dog likes this.

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