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  1. #1
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    ford 3000 JD5310 Ford947 JD5525 Farmall 400

    Default using a pressure guage as a scale.

    I'd like to put a pressure gauge on a JD 542 tractor loader to use as a scale to get a rough guide as to what large bulk bags of oats might weigh. I figure that will be better than a guess. Once I do some testing with some bulk fertilizer bags of known wt. and some known 50 lbs sacks of feed. So I figure that I should be able to weigh up to 2000 lbs using a pressure gauge. The 542 loader has two lift cylinders with a guess of 1 sq. inch each so I should be able to lift 2000 lbs with about 1000 psi. I don't want to take the cylinders apart to get the exact sq inch but I shouldn't have to. I know the loader lifts the ton bags of fertilizer but I have no idea of the pressure. Some of you guys have a lot of experience and I have none. Any idea which gauge to use or how much abuse a gauge can take. I was going to try a 3,000psi oil filled one But maybe that is to high. Will the gauge break if I stop it to fast on the way down and cause a spike in the pressure? Any ideas will be a help.

  2. #2
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    Default Re: using a pressure guage as a scale.

    Look at this Surplus Center

    If you wanting to leave the gauge on all the time, I would go with a 5000psi.

  3. #3
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    1984 Kubota B7200D (Sold 2015,) 2005 L39 Kubota, 2006 RTV 900 1997 Komatsu PC75UU2E w/ Thumb & Blade, 2013 Mahindra Max28XL Shuttle

    Default Re: using a pressure guage as a scale.

    Quote Originally Posted by Leejohn View Post
    Look at this Surplus Center

    If you wanting to leave the gauge on all the time, I would go with a 5000psi.
    General rule of thumb:
    2/3 of max pressure
    Attached Thumbnails Attached Thumbnails using a pressure guage as a scale.-20160810_185409-768x1280-jpg   using a pressure guage as a scale.-20160810_191901-768x1280-jpg  

  4. #4
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    Default Re: using a pressure guage as a scale.

    But what's the max pressure? that's what I'm trying to find out. If I have two cylinders each with one sq inch total 2 sq inches. I should be able to pick that up with 1000 psi. Am I think right?

  5. #5
    Elite Member
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    Default Re: using a pressure guage as a scale.

    Quote Originally Posted by wjkrostek View Post
    But what's the max pressure? that's what I'm trying to find out. If I have two cylinders each with one sq inch total 2 sq inches. I should be able to pick that up with 1000 psi. Am I think right?
    A bit more involved than that.
    Static analysis, levers and mechanisms, Free body diagram, geometry, etc. The loader is at a mechanical disadvantage. Google this stuff and if you get it, Freshman year Mechanical engineering will not be tough.

  6. #6
    Veteran Member the old grind's Avatar
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    Default Re: using a pressure guage as a scale.

    We can use 'repeatable' vs 'absolute' accuracy (think fuel gauge) so you shouldn't have to do much math to calibrate the gauge as a 'relative' scale.

    Raise a known weight say ~500lb to whatever height, read & write the weight/pressure. Load up a known, say twice as much or so to that height and note another pressure. Sketch/scale a graph and locate the two points. A third weight/point should tell you whether the line (wt/psi) is linear or parabolic. Connect the dots and look at the chart for any other numbers.

    Reading on your scale at what the FEL barely lifts should 'chart' as 'max capacity' of your FEL regardless of any affecting line friction or spool leakage that might mislead as to exact relief pressure. The numbers you see on the gauge or on paper are what you make of them. t o g

    btw, 5k psi gauge for 3k system for surge protection, esp if a suitable orifice or arrestor isn't installed.

  7. #7
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    Didn't intend to have a Deere fleet - it just happened 310C, F915,102 & 5200

    Default Re: using a pressure guage as a scale.

    Be aware the pressure reading will change depending on the loader position and position of weight on the loader.

  8. #8
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    Default Re: using a pressure guage as a scale.

    Shop around for a crane scale for your weight range. Here's one, for example.

    1KG 1Ton 2 LBS Digital Crane Scale Heavy Duty Hanging Scale w/ LCD Display | eBay

    Bruce

  9. #9
    Super Member 4570Man's Avatar
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    Default Re: using a pressure guage as a scale.

    The only way it would work with some degree of accuracy is if the load is centered the same distance from the pins and the arms are at the same height.

  10. #10
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    Default Re: using a pressure guage as a scale.

    I think your idea is too complicated and there is a much simpler alternative.

    Take a single hydraulic cylinder, fill it with oil and connect a pressure gauge to the cylinder port for retracting the cylinder. The shorter the cylinder the better as the piston is not going to move.

    The pressure gauge becomes the scale display and with a simple calculation of the retract piston area in square inches X your pressure gauge reading in psi should give you the weight in pounds.



    I am an engineer and I would find the calculations to use your loader itself just adding a gauge next to impossible as there are so many linkage angles that change and also the degree of level the tractor is on.

    Dave M7040

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