Pressure rating for OMC 1950’s tanks

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  • frankr

    US Member - 1 Year
    Replies: 6414
    Topics: 50
    #269622



    I believe the gasket would blow out long before
    pressure inside a tank reached the point that a tank
    could explode.
    Tubs
    .

    Tubs makes a good point indeed, seems like the gasket would blow out first before the tank could ever rupture.  Like others have pointed out, outboards are only capable of making a certain amount of crankcase pressure, which is relatively low.  Today’s volatile fuels combined with hot weather are probably more of a danger than excess crankcase pressure.  Like others have also pointed out, look at any of today’s plastic tanks that get bloated on a hot day, seems like the plastic would give way long before the sturdy two line pressure tanks of the 50s.

    All fuel systems have to be properly maintained, and vented properly to avoid fires/explosions.  My guess is that many fires/explosions were blamed on the pressure tanks, when maintenance, venting, and improper fueling were actually to blame.

    George:  I hope you get the information/specs you need to dispute this long standing myth about pressure tanks “exploding”, wish I could help.

    Amen.  My, how many tanks have I seen that have the bottom rim rusted away from sitting in the mud, blood, salt water and beer in the bilge.  It’s easy to imagine how the bottom could blow off.  In reality though, it probably starts leaking in the most rusted spot before it blows up.  You still get a boat full of gas though.


    billy-j

    US Member - 2 Years
    Replies: 141
    Topics: 19
    #269623

    What’s the difference between a 2 line pressure tank with the cap screwed on tight and a 6 gallon single line steel OMC tank sitting in the sun with the vent screw tightly closed? I will tell you. The 2 line pressure tank will vent to the atmosphere when the 4 to 6 pound pressure moves the relief check valve off it’s seat.  The single line tank will continue to build pressure beyond that. Looking to see when a tank explodes from pressure is not a realistic concern with a properly functional and maintained tank. Either tank set up if it built to much pressure would just push the carburetor needle seat off it’s seat and gas would leak out of the carburetor vent. It’s funny 2 line pressure tanks were never an issue till the single line tanks came out. The only problem with a 2 line tank is that they are 60 years old now and would be mechanics do not understand how they work and half ass try to fix them and do not know how to test them and get mad at them when it does not work right. To bad nobody wrote to that show Myth Busters and asked the to do a comparison of safety and pressure. Would have been an interesting show.  Regards Bill,


    crosbyman

    Canada Member - 2 Years
    Replies: 2991
    Topics: 287
    #269626

    personnaly the first time I started with oldies (10hp)  and 2 line tanks  I would park my tilted trailer   to drain rain water  out the boat and one   dayI found that 5 gal of gas  had drained out also.

    A small rusty pin hole under  pressure gave way and out came  the fuel during a hot summer day.

    Conclusion: 2 line tanks  are fine  just like  one line tanks  but  keep and eye on the bottoms. I was lucky  my drain plug was out and the fuel went into the grass ( no tgood  for worms, grass and water table)   but at least I did not go up in smoke.

    Joining AOMCI has priviledges 🙂

    • This reply was modified 1 month, 4 weeks ago by crosbyman.

    The Boat House


    Replies: 4074
    Topics: 102
    #269628



    No matter what documentation George my be able to provide,
    or even any demonstrations he may attempt to alleviate their
    concerns, I can tell you from past experiences, he’s not likely
    to change many minds. When fear is involved, better to be
    safe than sorry, trumps any evidence to the contrary.
    Tubs


    ede

    US Member - 2 Years
    Replies: 179
    Topics: 7
    #269664

    George, I believe you will need the engineering drawing for the tank.  It contains the specifications to include the grade of steel for construction.  I believe it will be a standard grade.

    Did OMC  stamp out these tanks or did they buy from a vendor and then finish assembly?

    The above thread does have merit for tank safety and as pointed out it is usually a human error.

    Ed


    frankr

    US Member - 1 Year
    Replies: 6414
    Topics: 50
    #269665

    What’s the difference between a 2 line pressure tank with the cap screwed on tight and a 6 gallon single line steel OMC tank sitting in the sun with the vent screw tightly closed? I will tell you. The 2 line pressure tank will vent to the atmosphere when the 4 to 6 pound pressure moves the relief check valve off it’s seat.  The single line tank will continue to build pressure beyond that. Looking to see when a tank explodes from pressure is not a realistic concern with a properly functional and maintained tank. Either tank set up if it built to much pressure would just push the carburetor needle seat off it’s seat and gas would leak out of the carburetor vent. It’s funny 2 line pressure tanks were never an issue till the single line tanks came out. The only problem with a 2 line tank is that they are 60 years old now and would be mechanics do not understand how they work and half ass try to fix them and do not know how to test them and get mad at them when it does not work right. To bad nobody wrote to that show Myth Busters and asked the to do a comparison of safety and pressure. Would have been an interesting show.  Regards Bill,

    Sorry, I beg to differ.  The metal single hose tanks had a pressure relief valve too.  Items 26, 27, 17.

     

    16.-Fuel-Tank

    Attachments:

    george-emmanuel

    US Member - 2 Years
    Replies: 469
    Topics: 35
    #269679

    Thank you Frank! I knew they did, but my focus was on the twin line tanks.

    Ed, thank you too! Any idea where those engineering drawings might be found? BRP probably is of no help since their entire focus was on corporate strategy.

    Still waiting to hear from Duke W.

    George


    ede

    US Member - 2 Years
    Replies: 179
    Topics: 7
    #269689

    George,

    You might get lucky and find them in BRP archives.  But, I afraid they are gone. There should be two part numbers, one for tank body and another for the bottom.  The ‘Bill of Materials’ on the engineering drawings will be the material specification.  I doubt that anyone at OMC did any sort of a fracture/rupture test. Point being many other things would have happened before tank fracture

    Ed


    george-emmanuel

    US Member - 2 Years
    Replies: 469
    Topics: 35
    #269690

    Update: Through other retired OMC top level folks I was able to speak with one of the engineers who is retired. Tanks had to conform to USCG requirements. So I went and viewed those and this is all I found:

    § 183.510 Fuel tanks.
    (a) Each fuel tank in a boat must
    have been tested by its manufacturer
    under §183.580 and not leak when subjected to the pressure marked on the
    tank label under §183.514(b)(5).

    I then viewed the labels on some tanks with good decals from the ’50’s and even the ones for my 1988 Johnson, and none had a pressure designation on the labels. Keep in mind that the USCG standards are updated to the latest, so maybe they weren’t in effect in those days.

    So if you wish to help, please see if any of the tanks you have, Mercury included, have a rated pressure stated on the label. The USCG requirement for testing was 150% of the rated pressure.

    George

     


    joecb

    US Member - 2 Years
    Replies: 679
    Topics: 74
    #269713

    George, Perhaps the USCG tank rules only apply to built-in fuel tanks. Our portable tanks may be an entirely different story, maybe not even under USCG rules?

    Joe B


    billw

    US Member - 2 Years
    Replies: 1961
    Topics: 63
    #269714

    Joe beat me to it. Today, and for as long as I can remember, tanks permanently mounted in a hull, have had a label that has a number of items listed, including a pressure rating. Since the tanks are often quite large, the pressure ratings are very low. We have a special device made up, that attaches to the vent fitting of a tank, and can use regulated shop air, to test the tanks. Generally, it is no more than 4 PSI, and even at that, the noises the tanks make under that pressure is scary.

    Long live American manufacturing!


    george-emmanuel

    US Member - 2 Years
    Replies: 469
    Topics: 35
    #269780

    Joe, you are correct about the test pressure. Actually, it is 3psi as stated by USCG, and I have a modern Tempo plastic tank that has the test pressure stated as being 3psi. Those pressures are used for testing leaks. But, that is not what I’m looking for and so far, even after talking to retired OMC engineers, there’s no answer to my question.

    If you were to go to court to prove a point, there would have to be confirmed documentation to support your argument. So far, I don’t have that documentation that says a tank is safe up to a specified (documented) pressure. So for me to say there is a safety factor of, let’s say for example, 3 to 1, with the vent pressure being 7-8psi, the rated working pressure of the tank would have to be 24psi (3 x’s 8psi).

    If we, as the Pioneering Authority, write articles, I’d like to know from my personal standing, that what I write is defendable..

    You folks are the best, and I appreciate all the wonderful comments and the fact that you all are interested!

    George

     

     


    stanley

    US Member - 1 Year
    Replies: 524
    Topics: 108
    #269800

    It occurred to me that my 80s 5 gal Eagle gas cans were similar in purpose and construction to the subject OMC outboard gas cans except they do not automatically vent.I called Eagle mfg tech dept. and they told me that every can they ship is pressure tested twice,once at 10 psig for leakage and then at 25 psig for structural integrity.I know this is not sufficient to answer Georges question,but might provide a little insight.


    george-emmanuel

    US Member - 2 Years
    Replies: 469
    Topics: 35
    #269806

    That does provide insight! I also have 2 Eagle 5 gallon cans, but from the early 1970’s. They have spring loaded caps over the fill spouts, and to fill, there is a notched bracket that engages with the handle used for pouring. That spring loaded cap acts as a vent!

    George


    stanley

    US Member - 1 Year
    Replies: 524
    Topics: 108
    #269812

    If you need more info,( I’m sure you’d ask better questions) just call them and ask for tech support.They were very responsive.

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