Forklift weight scale/pressure gauge?

I am thinking, that when the forklift holds a weight on the forks, the pressure in the main lift cylinder should be a linear function of
weight:
P = A + B * W
Does anyone make a product or some such that I can hook into the hydraulic line somehow, that would tell me the pressure and the weight of the item being lifted?
i
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Ignoramus8802 wrote:

Sure, most lift companies sell them. They are a calibrated gauge that attaches to the lift side of the ram. You pick the item up. Release the handle and the gauge reads out the weight in pounds/kilos. The mechanical ones work OK but they are hard to read sometimes. I like the electronic versions.
Electronic versions with a pressure transducer. http://www.americanforkliftscales.com / http://www.materialshandlingequipment.com.au/weight-guage / http://www.forkliftscales.us /
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Yea but you can't afford it. But maybe surplus...
During the Viet Nam war, I worked with a super guy that was on a contract. He was a lofty Physicist and had gotten the contract to build a force gauge that would measure the real tension on the bottom hook on a helicopter.
Cannons and pallets of sheet metal were being lifted all of the time and from time to time, a copter would drop under the load.
It wasn't a simple push/pull issue - twisting and rocking caused such effects that they were seen as much of the problem.
Strain gauges were used in a multi-axis link measuring the load. It was for the most part 4 axis - x,y.z,Theta. Rocking was a combination.
The unit, a digital scale is used to measure what truck tires press down = and like tasks.
Force cell or the like.
How would you add it ? complex.
One might have something on the forks - pressing backwards or bending. But the cylinder is the best spot - maybe a cell with two eyes - one for each end and inserts between the cylinder.
See if the forklift company has one on their website.
Martin
On 11/3/2011 9:04 PM, Ignoramus8802 wrote:

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On Thu, 03 Nov 2011 21:04:56 -0500, the renowned Ignoramus8802

WWW.SKIDWEIGH.COM
There may be others.
Best regards, Spehro Pefhany
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    There are liquid-filled (often glycerine) hydraulic pressure gauges. You would need to know the diameter of the piston to calculate the load from that, and of course subtract the empty load pressure from the pressure with an actual load in place.
    I think that the gauges go at least to 10,000 PSI.
    Here is one (3,000 PSI) on eBay for only $9.95: # 250921080861
    Here is a 10,000 PSI one: # 250796780436
    Don't worry about the air bubbles in there. That is needed to allow expansion when under pressure. (The bubble should get smaller as the needle goes upscale.)
    This one is a different design, and goes to 3,000 PSI: 280595831572
    Do a search on:
        Hydraulic pressure gauge
and there are a little over two pages of them.
    Or -- if you want to buy *new* -- check out Enerpac as a good maker.
    I would suggest starting with the piston diameter, and calculating the likely pressure range (multiply by two if the piston pushes a roller chain gear up) before ordering a gauge. I suspect that the lift does (or certainly *should*) not go to 10,000 PSI for example.
    Good Luck,         DoN.
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Don. thanks. I believe that I do not need to do any calculations. If I assume that P = A + B * W, then all I need to know to find A and B is the pressure with nothing on the forks, and the pressure with, say, 2 tons on the forks. Once I know A and B, I can make a little table on a card and put it next to the gauge.
For hydraulics, I would rather buy something new at McMaster for $40, than something unknown on ebay for $9.95 plus $8 shipping.
Thanks, though, for confirming that it is doable.
i
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I added such a gauge to my homebrew front end loader, to set the overload pressure relief which is somewhat temperature (viscosity) sensitive. The glycerine dampens vibrations from the hydraulic pump so the needle isn't a blur. If you mount the gauge in a panel or box it will be better protected from damage and you can mark the load weights around the dial and quickly see if the needle is nearing the max.
The gauge cost about $20 in a local hydraulic parts store.
jsw
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    [ ... ]

    [ ... ]

    Yes -- that would work -- except that I was suggesting a way to predict the top end of the scale -- do you need the 10,000 PSI one, or is a 3,000 PSI one all you need. The closer to the range of loads you need the more accurate your readings will be.
    Does the documentation for the forklift list the maximum hydraulic pressure allowed? Or the diameter of the piston? If only the latter, take that, convert to square inches, and divide into the maximum allowed load (plus perhaps an additional 500 lbs or so for the forks and carrier) to see what size you need.

    Have you priced the 10,000 PSI ones at McMaster Carr? Note that the glycerin filling is to damp vibration of the needle with the pumps pulsation.
    Looking at the McMaster Carr catalog, the glyderine filled ones range beteen $132.00 and $215.00 depending on size (2-1/2" or 4" diameter) and where the connectionis (bottom, center back or lower back. Ahnt it appears to e the same for pressure ranges between 30 PSI max and 10,000 PSI max. Expensive enough so you want to calculate the needed pressure range so you only have to buy *one*.
    These are on the web based catalog page 551.
    And no -- you don't want to use one designed for gas pressures as a hydraulic gauge.

    I've seen presses for forming something or other at work with such a gauge mounted on it. You could also add one to a hydraulic arbor press ('H' press) or the like. But you do need to know the maximum pressure needed or allowed -- and a bit over that so you can tell between right at the limit and the needle pressing hard against the stop pin. :-)
    Looks as though there are silicone oil filled ones, as well as the glycerine ones in the McMaster Carr catalog.
    Good Luck,         DoN.    
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