Shop weight scale
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From: South TX
Shop weight scale
Hey yall- Does any body have or know of a good scale for weighing vehicle or trailer axel weights? Saw one somewhere awile back, that was like a hocky puck with a gauge on it. You could put it on a floor jack or under a trailer toung to see what kind of weights you're dealing with. Getting kind of tired of driving 20 miles to the nearest commercial scales. Also had this idea that I could modify an hydrolic bottle jack with a pressure gauge to calculat weights with it. Think this could work?
Seems to me that if you knew th exact sq.in. area of the bottom of the piston, and a psi gauge, you could calculate the weight.
Though I'm certainly no fluid expert, I believe that the pressure on the fluid is equal in all directions, relevant to the pressure applied. Any thoughts?
(I think this was the concept behind the "hocky puck" scale that I can't find again)
Seems to me that if you knew th exact sq.in. area of the bottom of the piston, and a psi gauge, you could calculate the weight.
Though I'm certainly no fluid expert, I believe that the pressure on the fluid is equal in all directions, relevant to the pressure applied. Any thoughts?
(I think this was the concept behind the "hocky puck" scale that I can't find again)
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Hi Ultraute,
Your idea of using a hydraulic piston and a pressure gage is right on the money. I have seen and used this method of weighing things many many times. The setups I am familiar with were used to weigh very heavy, large items, say in the 50 ton and up range. But there is no reason I can think of why it wouldn't work to weigh a truck or trailer.
PbFoot
Your idea of using a hydraulic piston and a pressure gage is right on the money. I have seen and used this method of weighing things many many times. The setups I am familiar with were used to weigh very heavy, large items, say in the 50 ton and up range. But there is no reason I can think of why it wouldn't work to weigh a truck or trailer.
PbFoot
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There are inaccuracies in the gauge, piston area, and seal friction, otherwise it will work. Get the smallest jack (smallest ram) that will lift the object. The smaller the ram the greater the pressure difference due to weight changes. If you want to weigh axles in the 2-10,000lb range you would need a 5,000lb jack (one side) or 2.5T or 3T jack, not some 20T jack.
It is more accurate if you weigh both sides at once to avoid weight transfer tho.
p.s. I teach industrial hydraulics.
It is more accurate if you weigh both sides at once to avoid weight transfer tho.p.s. I teach industrial hydraulics.
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From: South TX
Hey, this is goodnews! Thanks for the reply guys. Now if only I can find a jack with a one square inch ram/piston (1.1284 inch dia.) I wouldnt even have to calculate psi to pounds. I think I'm gonna try this, and see how it works.
Will let ya know, if, when, and how.
One more question though, If the bottom of the ram is flat, then figureing area is no prob. But if it's concave or convex, will the pressure be relative to the area of the end, OR to the area of the diameter?
Torque1st ??? Anybody?
Will let ya know, if, when, and how.
One more question though, If the bottom of the ram is flat, then figureing area is no prob. But if it's concave or convex, will the pressure be relative to the area of the end, OR to the area of the diameter?
Torque1st ??? Anybody?
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So the cylinder bore area, (reguardless of piston/ram end configuration) IS what the area vs pressure ratio is???
Convex, concave, or waffel surface ares do not count??
It's the area of the cylinder bore area that counts? Yes?
Convex, concave, or waffel surface ares do not count??
It's the area of the cylinder bore area that counts? Yes?
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From: South TX
Thanks, that is what I thought. Am going to experiment with this soon.
going out to look for jacks and gauges now.
going out to look for jacks and gauges now.
Originally Posted by Torque1st
Yes, the area of the cylinder bore.
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There are usually welded up ports on the side that a passage can be drilled thru or you can drill your own passage.
Once you know the area of the cylinder bore and the weight the jack will lift you can back calculate the pressure on the fluid. This will tell you what pressure gage you need.
I have to stress here that the accuracy of the gage and the friction in the seals will limit the accuracy of the system. The weight readings you get will only be ball park figures and you should check them with a certified scale.
Once you know the area of the cylinder bore and the weight the jack will lift you can back calculate the pressure on the fluid. This will tell you what pressure gage you need.
I have to stress here that the accuracy of the gage and the friction in the seals will limit the accuracy of the system. The weight readings you get will only be ball park figures and you should check them with a certified scale.
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Haven't built mine yet,(few other chores in line ahead of this) But I'm sure going to try this.
So Torque1st,
Wouldn't a larger ram(reduced PSI for a given weight) allow for a lower scale gauge, that should be more accurate?
In other words, say a 2.0 sq.-in. face (100 lbs= 50psi) or even 1.0 sq.in. (1 to 1) Be better than a small bore of say 0.5 sq.in?
And as for the seal friction, unloaded, I can push the ram down with just a few pounds of pressure. How much do you suppose the friction increases under load?
Thanks for all your advice so far!
So Torque1st,
Wouldn't a larger ram(reduced PSI for a given weight) allow for a lower scale gauge, that should be more accurate?
In other words, say a 2.0 sq.-in. face (100 lbs= 50psi) or even 1.0 sq.in. (1 to 1) Be better than a small bore of say 0.5 sq.in?
And as for the seal friction, unloaded, I can push the ram down with just a few pounds of pressure. How much do you suppose the friction increases under load?
Thanks for all your advice so far!
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Like I said above, you need a jack with the smallest ram to make the pressure change the greatest. You need a gage with the proper pressure rating for the jack because you know someone will try to jack up something with it.
Seal friction is affected by pressure depending upon the type of seal used.
Seal friction is affected by pressure depending upon the type of seal used.
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From: Oregon
I built a pressure testing ram for preloading anchor rods. Used a 50 ton Harbor Freight 2 speed bottle, (like Eric was saying, this is too big for a truck, but just right for 125k with fulcrum.) Suprisingly, I was able to call a guy at Harbor Freight who actually knew something about their rams - like internal bore size, release valve rating, etc. (Not the local store, but at the central office.) He even knew the internal specs in case I wanted to tap a larger hole. It's pretty accurate as it get's closer to load. At low load the needle just doesn't move enough for accurate readings. I went to the local fluid connector store to get a quality gauge and some stainless tubing/fittings, so I could mount the gauge where I could see it well.