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Questions about LP72 tanks

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

  1. spectrum

    spectrum Dive Bum Wannabe ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: The Atlantic Northeast (Maine)
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    Passion is a beautiful thing. Mary that with talent and knowledge and good stuff happens.
     
    lowviz likes this.
  2. Eric Sedletzky

    Eric Sedletzky Great White

    # of Dives: 500 - 999
    Location: Santa Rosa, CA
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    I must be lucky because I've never got any 72's that had a liner.
    I've had many 72's given to me by people thinking they were old and obsolete. I gladly take them and use them. I've also purchased many when I see a good deal. The only ones I keep after the intial 5 year hydro time are the 3/4 valve galvanized tanks. The 1/2" taper thread or painted tanks I sell after the first hydro comes up.
    I have never had a 72 fail hydro.
    My dive shop will fill them to 2800 to 3000 no problem.
    They are my all time favorite tank for quick easy shore dives especially if any hiking is involved. I just love them.
     
  3. FireMedicATL

    FireMedicATL Solo Diver

    # of Dives: I just don't log dives
    Location: Livonia, MI
    351
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    Liners happen, there is one on my tumbler right now with a liner. It will be gone by morning. They aren't the end of the world, just more work than most are willing to do.
     
  4. Eric Sedletzky

    Eric Sedletzky Great White

    # of Dives: 500 - 999
    Location: Santa Rosa, CA
    3,407
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    What are you using for media?
     
  5. lowviz

    lowviz Solo Diver

    # of Dives: 200 - 499
    Location: Northern Delaware or the New Jersey Turnpike
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    I read right over this when you posted it and it didn't "click". Just noticed it. Please elaborate...
     
  6. Luis H

    Luis H Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: Maine
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    Between those two options, it is definitely not the first option.

    ---------- Post added August 28th, 2015 at 10:56 PM ----------

    I wrote this at VintageDouble Hose.com on May 8, 2010.
    Vintage Double Hose

    Most of the blanks in the spread sheets have been filed. Since I just did a lot of hydro tests earlier this year (5 years later), I have a newer data sheet for the cylinders. The REE numbers will not change and the old hydro data is still part of my tank records.

    Note: In about a week I am actually going to do hydro test on the few tanks that will be needing fresh hydros fairly soon. My LDS with the hydro equipment is closing their doors in about a month. This is bad news in many ways.


    _________________________________________________________________

    From May 8, 2010:


    I spent the day yesterday doing hydros on seven of my tanks. My LDS has a hydro station that I use… I still pay for the hydros, but I do the work and control the duration of the pre-test, etc. I like doing my own hydros.

    I also got wall thickness readings on 9 of my steel 72. A co-worker took the readings using a precision ultra-sound NDT equipment. I drew a pattern of dots on my tanks and took reading every 3 inches to get a precise average.

    This procedure meets (and exceed) CGA C-5 in determining an average REE for this class of tanks. I own enough Norris and PST steel 72 tanks that I can calculate an average REE number for the type of tank (per the CGA procedures). Whether your local hydro station accept this REE number to plus “+” stamp your tanks or not, I don’t know. You are always welcome to bring them up to Maine I can recommend a nice dive shop that would gladly hydro them with the + stamp for you (assuming it meets the criteria, which probably does).

    All but a few of my 3AA tanks are already + stamped. By the after the next hydro I expect all my tanks to be plus stamped, including my 45s and 40s double tank sets.


    Below is some of the data on my tanks. There is still a lot of empty blanks, but I should have at least one data set for all of my tanks by the end of the year or early next year.

    In the first two tables each row is for the data associated to a tank. The third table is in columns; with each column has the calculations for the tank identified on the top. On the far right of table three shows the equations used in each column.

    Tank dimensions and wall thickness:

    [​IMG]


    Tank hydro data and volume data:

    [​IMG]


    Tank REE and hydro calculations:

    [​IMG]



    more later
     
  7. FireMedicATL

    FireMedicATL Solo Diver

    # of Dives: I just don't log dives
    Location: Livonia, MI
    351
    75
    28
    To remove liners? 1/2" hex head sheet metal screws. About five pounds, tumbled on a 30 degree angle. Clean and dry as normal.

    Sent from my GT-P5113 using Tapatalk 2
     
    Eric Sedletzky likes this.
  8. Luis H

    Luis H Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: Maine
    2,783
    871
    113
    ________________________________________________

    I wrote this on November 24, 2010:



    I have 14 steel 72 tanks that I have been taking some precise measurements.

    Wall thickness measurements were taken using a precision ultrasound measuring device. The ultrasound probe was calibrated before each set of readings using a cut off (condemned) steel 72 tank. The cut off tank wall thickness could be confirm with a caliper and provided a sample of the exact same material to calibrate the ultra sound equipment. Measurements are good to about 2/1000 of an inch.

    I measured the actual internal volume by using water at room temperature and precisely measuring the weight of the water. I took into account the reduced volume from the valve threads.

    I am only showing some of the data below to save space. The “Tank #” is only the number I assign and painted on all my tanks to keep track of them. I have full records (in a spread sheet) with all the tank information, including serial number and all the tank markings (including all the hydro test markings).

    I also have records of all the hydro test data, etc.

    I am only including seven of my tanks at this point (plus a friends Walter Kidde tank). I still need to take precise volume data on the other tanks. I do have wall thickness for all of them. I need wall thickness and volume data to calculate REE numbers for that specific tank.

    At this point I have complete data for four Norris tanks, three PST tanks, and a friends Walter Kidde tank (I don’t own any Walter Kidde).

    The data is shown as follows:
    Tank# / manufacturer >> average wall thickness / tank empty weight (with boot and valve) / tank actual volume at 2475 psi / actual REE nunber

    1 / Norris >> 0.177 inches / 30.26 Lbs / 72.2 cu ft of air (@ STP) / REE = 61.3
    2 / PST >>>> 0.171 inches / 28.88 Lbs / 70.5 cu ft of air (@ STP) / REE = 58.6
    4 / PST >>>> 0.181 inches / 30.11 Lbs / 70.8 cu ft of air (@ STP) / REE = 61.5
    5 / Norris >> 0.179 inches / 29.73 Lbs / 71.4 cu ft of air (@ STP) / REE = 60.7
    6 / PST >>>> 0.173 inches / 30.43 Lbs / 70.9 cu ft of air (@ STP) / REE = 58.7
    7 / Norris >> 0.178 inches / 31.01 Lbs / 70.3 cu ft of air (@ STP) / REE = 58.4
    8 / Norris >> 0.175 inches / 29.73 Lbs / 71.4 cu ft of air (@ STP) / REE = 61.2
    No# / WK >> 0.183 inches / 29.63 Lbs / 71.0 cu ft of air (@ STP) / REE = 63.6


    The variation in volumes is not very much considering the manufacturing process used for these tanks. As a mater of fact I consider the variation in wall thickness to be fairly impressive. The wall thickness standard deviation for the data collected for each tank is also relatively small.


    Tanks with a + stamp (DOT 3AA code) are always advertised as having the capacity with the extra 10 % overfill.

    An interesting side note. I also measured two PST HP 80s. They are supposed to have 80 cu ft of air at 3442 psi… they actually have 85.3 cu ft and 85.0 cu ft.

    Note: as expected, the actual REE numbers are all higher (or equal) to the published number by PST. As a mater of fact I believe the REE number on tank 7 came out low due to lack of precision on the hydro test data. I believe I had a tiny leak during hydro, but not bad enough to do it over. I will confirm the data in 5 years.
     
  9. spectrum

    spectrum Dive Bum Wannabe ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: The Atlantic Northeast (Maine)
    11,373
    811
    113
    The hot dipped galvanized coating creates properties that confound a standard hydro static test and can lead to an unwarranted failure.

    To get around this PST prescribed a rounding procedure that pressurizes the cylinder then relaxes it before the actual hydro static test. This is roughly analogous to doing stretches before weight lifting.

    The procedure can be seen here in post #12.

    Pete
     
  10. lowviz

    lowviz Solo Diver

    # of Dives: 200 - 499
    Location: Northern Delaware or the New Jersey Turnpike
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