using a pressure guage as a scale.

   / using a pressure guage as a scale. #1  

wjkrostek

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Mar 15, 2004
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palmer ak
Tractor
ford 3000 JD5310 Ford947 JD5525 Farmall 400
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.
 
   / using a pressure guage as a scale. #2  
Look at this Surplus Center

If you wanting to leave the gauge on all the time, I would go with a 5000psi.
 
   / using a pressure guage as a scale. #3  

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   / using a pressure guage as a scale.
  • Thread Starter
#4  
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?
 
   / using a pressure guage as a scale. #5  
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.
 
   / using a pressure guage as a scale. #6  
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.
 
   / using a pressure guage as a scale. #7  
Be aware the pressure reading will change depending on the loader position and position of weight on the loader.
 
   / using a pressure guage as a scale. #9  
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.
 
   / using a pressure guage as a scale. #10  
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.

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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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