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Questions about LP72 tanks

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

  1. Scared Silly

    Scared Silly Regular of the Pub

    # of Dives: 500 - 999
    Location: on the path to perdition
    Any lining in a cylinder is a counter indication for filling for with anything but air. Also it is basically impossible to 100% remove the lining. And if you do more than likely material from the wall will have been removed. Thus degrading the structural integrity.

    As such, it is best to avoid lined cylinders. Some have yellow rubberized coating on the outside as well.
  2. eelnoraa

    eelnoraa DIR Practitioner

    # of Dives: 100 - 199
    Location: San Francisco Bay Area
    In SF bay area, I won't recommend LP72 tank. First, it is unlikely you will find + rating LP72 in our area as well. And like others mention, you get 64.7CF at 2250 rated pressure. This is all you will get in dive shop area here. Overfill LP72 is very rare practice here. Of ~65CF is what you need, sure, go for it. They are usually very inexpensive. If you can, I would say go for tank like LP85s. They are not as expansive as HP100. Quite a few shop will fill them to 3000psi, so you get 90+ CF. Pretty good tanks for our water
  3. Ouvea

    Ouvea Solo Diver

    # of Dives: 1,000 - 2,499
    Location: CA, USA

    I do not recommend that you purchase 72cft tanks. I understand that your wife has a very efficient SCR/SCA. However, you need to account for the gas requirement of two divers. You will find that 72cft tanks seriously limit your bottom time, as your required minimum gas will limit your usable gas.

    A pair of HP100 will serve you better in our area. Diving at greater depth will show you the limitations of a 72cft tank. This the primary reason why I migrated away from my 72cft tank.

    In regards to the finish, hot dip galvanized such as the PST or the Worthington tanks have proven more durable than the painted finish of the Faber tanks. Unfortunately, PST and Worthington have gone by the wayside, leaving Faber as your only choice.

    Rest assured, you will be able to easily handle an HP100. I have made many dives at Monastery Beach with my HP100s (I measure 5'5 @ 130lbs).

    dead dog likes this.
  4. elgoog

    elgoog DIR Practitioner

    # of Dives: 200 - 499
    Location: San Francisco Bay area
    Thanks for all the info so far!!I've arbitrarily decided to disregard tanks that haven't been hydro'd in this century, so I think I should be mostly OK on the rust, bubbling, pitting issues. In any case, definitely going to take the boots off to check. I'm in no rush whatsoever to acquire the 72s. My primary search right now is for LP 80s or 85s.Due to the lower weight and cost and her lower air consumption, the 72s are a useable option for my wife. Our shore dives max out at ~60ft and average ~35ft, anything deeper requires a swim longer than I'm comfortable with in a single tank anyway. Min gas for that works out to just under 30cu.ft for us and, assuming a reasonable fill, this gives her about 35-40cu.ft useable gas and me 50-55cu.ft. This is very close to the air consumption I've recorded for us so far.

    HP100s are the goal - the pennies are starting to get pinched for that as I type this :) I'm trying to find tanks in the $100 (total, ready to dive) range in order to get us started and move away from rentals.
  5. DA Aquamaster

    DA Aquamaster Directional Toast ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: NC
    Bolded red text:
    If you are talking strictly about liners for steel 72s, that's true.

    However, if you are talking about tanks in general, that isn't strictly the case - liners have been used in some O2 tanks for years, and type IV composite tanks with PET liners are currently being developed for aircraft O2 use.

    Bolded black text:
    That's the popular misconception among many dive shops and it's why many will refuse to tumble them to remove the liner.

    It takes a lot of tumbling so it's an inconvenience for them, particularly when they'd rather sell you a shiny new aluminum tank.

    The tough spot for liner removal is at the base of the tank, where the action of the media is least pronounced. However that's also the area where you can get at the liner with a wire brush, so it's a wash. And more to the point, if a small bit of liner is hard to remove, it's also obviously well adhered and not compromised, meaning you won't have a pit under that remaining bit anyway - and the tank is thickest in that area already.

    Fears of removing steel from the inside of the tank in the process and compromising the integrity of the tank are however completely unfounded. You'd have to tumble a steel tank with an aggressive media for a couple months to have any effect on the integrity of the tank.

    ---------- Post added August 26th, 2015 at 09:15 AM ----------

    In a perfect world, yes, you'd make the small wife carry the enormous tank to ensure the hoover husband has ample reserve gas in her tank. That will have the effect of negatively impacting her sac rate, reducing the difference in sac rates, but not in a good way.

    Consequently, in the real world, the small wife will dive a smaller tank well suited to her stature, while the hubby carries a larger tank. The buddy team will then gas match to ensure that the reserve the wife retains in her tank will be large enough to get both team members to the surface in a lost gas situation. The part of the quote in bold is the only part that really applies.
    duckbill likes this.
  6. halocline

    halocline Solo Diver

    The appeal of the LP72 is that it weighs only 26 lbs on land, as opposed to around 34 for a HP100, and the size is substantially smaller. For shore dives by small divers with good air consumption, LP72s are excellent. I use them all the time in a local spring.

    Ironically, probably the closest current tank in terms of ease-of-lugging and overall feel underwater would be an AL63, which I also like using for shallow shore dives.

    To the OP, forget the nonsense about having your wife carry a huge tank because you-not her- might need the extra air. This is open water diving, right? She'll be much happier lugging around a smaller tank.

    Most of the 72s I've seen are painted over a galvanized primer. It's very easy to remove the outer paint and leave the primer; you can then spray a bit of ZRC galvilite cold galvanizing compound on them. I did this maybe 10 years ago to several 72s and they're still in perfect shape. If you can find PSTs there is a document floating around that has the REE number for them, which means a decent hydro shop should be able to give them the plus rating. Finding the REE number for the walter kidde and norris 72s might be very difficult, and finding a hydro shop to give them the plus rating without having the REE number from the manufacturer will be next to impossible.

    But, on the bright side, I haven't found much, if any, difference in getting fills for my plus rated PSTs and my non-plus rated WKs. Shops around here sometimes just fill them to 3K, on the assumption that all tanks in the known universe are AL80s, or 2250, on the assumption that the plus rating is the devil's mark and should be exorcised.
  7. DA Aquamaster

    DA Aquamaster Directional Toast ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: NC
    I still have 6 steel 72s from my early days of diving, and I now regret trading 4 of them off for LP 95s. For local side mount dives, and in smaller cave like Jug Hole, they are near perfect tanks.
  8. FireMedicATL

    FireMedicATL Solo Diver

    # of Dives: I just don't log dives
    Location: Livonia, MI
    How many would you like? I sell them for 75 each and I can ship. I have about twenty for sale at the moment.

    ---------- Post added August 26th, 2015 at 06:55 PM ----------

    Since there seems to be a lot of confusion about good old steel 72s, let us try and set the record straight.
    Liner or no liner, doesn't matter much. The liners tumble out overnight. I have never had one I couldn't remove. You will not cut into the wall enough to harm the tank in the time it takes to remove a plastic liner.
    Whether or not your LDS is capable, that is a whole different boat.
    The only thing that kills a 3AA tank is rust, inside, outside, doesn't matter where, but if you don't see rust, assume you have a good tank.
    I have hydroed at least 100 72s in the last three years and I have had ONE fail hydro, several have failed visual inspection due to rust, but just one on the hydro end. (That tank still befuddles me, it is beautiful,it must have been overpressured to the moon sometime in the past.)
    As to the plus hydro, they should not be getting one. Period. End of story.
    The Manufacturers of steel 72s are no longer in the business, there is no way to confirm an REE number.
    The PST document that is often alluded to has a misprint on the tank pressure line for the steel 72 tank. There is no other version that I have seen. With the misprint and no way to confirm it with PST, that document is invalid.
    Any retester doing this for a living is not going to risk his license to plus stamp a 40 year old scuba tank for somebody.
    If they are willing, that is on them. The problem lies in that they have no paperwork should they ever be called to point on their decision.
    duckbill likes this.
  9. Luis H

    Luis H Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: Maine
    Hi DA Aqua Master,

    I agree with most of your post, but I have a small correction. The test pressure fore 3AA cylinders is 5/3 of the stamped pressure.

    2250 psi , hydro test pressure is 3750 psi (the +10% working pressure 2475 psi)
    2400 psi, hydro test pressure is 4000 psi (the +10% working pressure 2640 psi)
    3000 psi, hydro test pressure is 5000 psi (the +10% working pressure 3300 psi)

    I have several different sizes of 3AA cylinders. I have 16 steel 72, one large ugly LP cylinder stamped with 2400 psi and 6 (3 pairs of different sizes) stamped 3000 psi. All of my 3AA have current legitimate + stamp.

    I am very comfortable filling my steel 72 (stamped 2250 psi) to around 2800 psi. I always like to leave a reasonable safety margin.

    The hydro test pressure takes the cylinder to the lower range of the material yield strength. The purpose of the hydro test is to actually verify the material lower yield strength limit. This checks the material condition (for work hardening or heat/ fire damage that could have affected the heat treatment).

    All of my steel 72’s are either PST or Norris. I don’t own any Walter Kidde, but I have hydro tested two for my neighbor.

    BTW, the actual capacity of my steel 72 (at 2475 psi) range from 69.6 cu ft. to 72.2 cu ft. The average is around 70.8 cu ft. (about half of my cylinders are PST and half Norris). I tend to round the average capacity to 71 cu ft.

    Note: I don’t agree that the internal liner has to be removed. It only need to be removed if there is any suspicion of any rust under it. Many liners are very smooth and it is obvious if they are compromised. Dark liners make it hard to do a VIP, but is not impossible.

    Hi FireMedicATL,

    I agree with most of your post except for the comments about the + stamping. All my steel 72 have current and very legitimate + stamp. I strictly followed the CFR (Code of Federal Regulations) procedure to calculate the REE numbers for all of my steel 72’s and submitted them to my local licensed hydro facility (paper copy for their records). I even showed them to the regional DOT inspector and offered to stamped them with my PE (Professional Engineer) licensed number, but she found the calculations spread sheet to be more than adequate by itself.

    To do the calculations, we measured the average wall thickness using ultra sound equipment (I took the average of 20 data points per cylinder) and precisely measure the internal volume of each cylinder using the water weight.

    The average (sample size: 6 cylinders) REE number for my Norris cylinders is 60.1

    The average (sample size: 4 cylinders) REE number for my PST cylinders is 59.6 (and the lowest number was 58.6)

    I have not read the CFR in a while, but I think it only required a sample of 3 cylinders (from a particular type: same size, manufacturer, pressure, etc) to determine the REE number for that type of cylinder. From what I recall, it did not required them to be from the same batch or year or anything similar, just the same type.

    I will be glad to provide sample calculations in PDF or Excel spread sheet.

    Note: CGA (compress Gas Association) publication C-5 provides a lot information and guidance on methodology for getting cylinder data and how to calculate the REE numbers.

    The published REE number from PST is 58.4. Yes, there is a typo in the pressure, but it is pretty obvious that it is just a typo. All the other data matches the steel 72. I think that I remember showing it to the DOT regional inspector (for our North East region) and she didn't seem to be concern about the typo. It might have helped that I had a substantial amount of other related cylinder data, but I am not sure.

    To the OP,

    The steel 72 is a great cylinder. You can probably tell how much I like them. They hold plenty of air for me for most any shore or local boat dive.

    My wife actually prefers the HP 80 cu ft (her PST cylinders actually hold 85 cu ft at 3442 psi). They require less over all weight and she likes the short cylinder.
    Last edited: Aug 28, 2015
    macado, couv, lowviz and 3 others like this.
  10. FireMedicATL

    FireMedicATL Solo Diver

    # of Dives: I just don't log dives
    Location: Livonia, MI
    I will stand corrected. I have never, nor have I ever known someone to calculate the REE for a given tank. If presented with it, I would read through the cfrs and make sure it was done correctly and is legal to do, if so, the plus would be given.

    You either have a lot of time on your hands or you like 72s even more than I do.


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