Made a "Forklift Scale" for the working poor

Ever since I decided to get more into scrap metal, I always wanted to add a weight scale to my 15k forklift, so that I would instantly know how much am I lifting.
That way I could learn estimating a lot quicker, and also avoid those overweight truck fines. We almost got his with one, with cops weighing the rear axles at 33,100 lbs, so close to the 34,000 lbs limit.
The problem was that the scales are expensive, starting from $730 and up. And all they do is measure the cylinder pressure and convert that into lbs, according to a linear formula.
So, instead, I took advantage of an opportunity, since the main cylinder hose on my forklift was leaking a bit and needed to be replaced. I took a "precision temperature compensated 3,000 PSI pressure gague", that I had laying around. When replacing the main hose, I added a tee and hooked up the scale into that.
So, now I always know the main cylinder pressure. I am going to weigh a few things of known weight (I do have a 10k floor scale, so it not hard to come up with known weights). Then I would write up a table of weight/pressure values and run a linear regression, then I would print out a table with these values. That way we'll know for sure what weighs how much.
I did hook all of that up yesterday, but did not yet play with this due to lack of time, but I plan on doing so shortly.
i

Ignoramus32392 wrote:
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Print up a new scale for the pressure gauge so the weight can be seen at a quick glance rather than referring to a chart. Also make sure you put a pressure snubber orifice in the feed to the gauge to help protect it from pressure spikes.

"Pete C." wrote:
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A shutoff valve for the gauge is also a good idea so you can shut it off if you're doing rough work that will generate a lot of pressure spikes, and also if the gauge fails you can easily shut off the line and replace the gauge.

On 4/7/2013 8:10 AM, Pete C. wrote:
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I agree with Pete on the shut off. Use a needle valve. Also, if the gauge is oil-filled, the shocks won't damage it. there was an oil filled gauge on the main cylinder of a hydraulic plastic injection molding machine I used to have. Believe me, there was lots of shock there!
Paul

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The gauge is NOT oil filled.
i

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OK, the "new scale" is a good idea. The pressure snubber is something that I never heard about. I would think that the forklift hydraulics is somehow protected from pressure spikes, anyway?

On Sun, 07 Apr 2013 11:12:07 -0500, Ignoramus32392
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I've done something similar. My gauge was oil filled and on the end of about 8' of flex hose, no snubber. Gauge did bounce a little but was fine for years.

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Hoses expand and contract more than one might assume, based on their pressure ratings. The hose (that long) WAS the 'snubber'. Essentially, the same as adding a small air accumulator near the gauge, but using the flexibility of the hose instead of the compressiblity of air to do the absorbing of the spikes.
Lloyd

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Ig, since the math is simple (and you, especially, know that), I'd suggest that instead of making up a table for your work-a-day weighing, you do it only once to determine if there are any non-linearities (in the gauge... the cylinder will be linear), then make a replacement SCALE for the gauge itself.
If you don't want to disassemble the gauge, you can just make it from transparent label stock, and stick it on the glass.
LLoyd

"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> fired this volley in
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Hmmm... servers must've delayed messages. I see that Pete C suggested the same thing.
He's right about the snubber and cut-off, too.
Lloyd

On 2013-04-07, Lloyd E. Sponenburgh <lloydspinsidemindspring.com> wrote:
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Yep, I will do that indeed.
i

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You might check if the indicated weight varies going up or down, or close in vs out at the tips, from friction. jsw

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Yes, it does, I just checked. It varies by 20 PSI. Not that big of a deal, and it is very consistent.
i

On Apr 7, 10:06 am, Ignoramus32392 <ignoramus32...@NOSPAM. 32392.invalid> wrote: >
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I would be interested is knowing how linear the weight / pressure is. Where I worked they have a sling test tower where they proofed and certified weight handling gear. I am pretty sure they ignored any possible non linear effects and just multiplied the pressure by the area of the piston. And I have always wondered how accurate that approach was. Have also been involved with making small weight scales to go under each wheel of a race car to set up the suspension. There of course one does not need absolute weight.
Dan

On Sun, 7 Apr 2013 11:04:41 -0700 (PDT), " snipped-for-privacy@krl.org"
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We low-buck racers used a bathroom scale and a 2 x 8 with a fulcrum. A mess to set up, but it worked.
And I made my own tire-temperature gauge with a 1N914 diode for a sensor and an op-amp and analog gauge. Accurate to within a degree or so, and dirt cheap.
1N914s, unlike thermistors, are linear as hell and they respond in about one second to tire temperatures. Leads must be short, however.

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It is not a lot of money to make a cylinder out of aluminum, make a piston using an O ring for the seal ,and connect it to a pressure gage. I think we made a set of four and spent less than $10 per wheel, not counting engineering and manufacturing time. It was worth while for circle track racing where you were adjusting the suspension often. Might not be worthwhile for sports cars.
Dan

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It's cheaper in mistakes and time to buy PortaPower shorty cylinders, and convert them to purpose. They're rated at 10Kpsi.
LLoyd

On Apr 7, 3:17 pm, "Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote: >
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But not as much satisfaction in having made something. The 10kpsi would have been wasted. The car weight was about 2000 lbs and only about 500 psi per wheel.
Dan

OK, I changed the non-liquid-filled 3,000 PSI valve, for a liquid filled, stainless 5,000 PSI valve. I think that it will "do it".

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I did essentially the same thing in reverse when we needed a 0.01g balance at work ASAP, and the one we ordered was a week away.
I built a small lever/fulcrum arrangement from K&S brass stock and sewing needles that multiplied the force by 10X.
Of course, we were working with a total load of only 2g <G>.
LLoyd