Corner weight vs axle weights

[markopolo]

No problems with spinning at all. The parking brake was on, transmission in park, another wheel chocked front & rear just in case. Garage floor is level.

Anything less than 3/4" ply would likely bend too much. 3/4" ply plus 2.25" ram matches double stacked 2X lumber nicely. 7/8" ply might be ideal to allow for compression.

For any object weight registering under 500 psi I'll have to subtract in 50 psi decrements from 500 psi until it meets the dial position.

That changes the trailer tongue weight calculation I previously posted. The new calculation would be 350 psi x 2.25 square inches = 787.5 lbs. I can use this info to figure out how to optimally load the trailer.

[markopolo]

The rear corner weights might have been the most accurate of the weights taken today as all 4 wheels were at the same height off the garage floor. The side to side weight difference was only around 56 lbs.

Passenger side rear 950 psi x 2.25 sq in = 2138 lbs
Driver side rear 975 psi x 2.25 sq in = 2194 lbs

passenger side rear 950.JPG driver side rear 975.JPG

Various rear weights for this van over the years:

In 2011 at the truck scales: nearly empty & probably not much if anything added by me to the van yet
Rear: 3860 lbs

In 2013 at the truck scales: fully loaded, including cargo box and bikes
Rear: 4780 lbs

In 2016 at the truck scales with travel trailer attached by weight distribution hitch:
Rear: 5000 lbs

Today in garage, lightly loaded, no water, full diesel
Rear: 4332 lbs

[booster]

I was just looking at Harbor Freight, and they also have a 20 ton version of the ram, which I think would put you on a 1000 psi gauge for 4000# capacity, if I estimated the cylinder size base on doubling the 10 ton area, Hopefully, you could get higher resolution of pressure that way.

[markopolo]

So far I've found that you can get 20 psi increments on (up to) a 1500 psi analog gauge. The max weight measured using the 10 ton ram with that gauge would be 3375 lbs. That's good enough for my van corner weights. If the 20 ton ram has a larger cylinder area then the max weight capacity would increase. The higher multiplier could magnify reading errors. It looks like you can get 10 psi increments on a 1000 psi gauge.

A digital gauge would be ideal but that turns a $50 project into $200 plus easily. Accuracy would be much better though.

[booster]

It does look like the 1500# gauge would give the best results. It would use the maximum amount of range on the dial, which always gives better resolution and guesstimation between lines.

Always be careful when you look at the digital gauges for any purpose. Often they have no better resolution or repeatability than the analogs, if they are low end stuff. A prime example is a digital caliper. Most dial ones read to .0005", and digital ones will read .0001" or even 00005" in some cases, but both style will have accuracy and repeatability considerably higher than the smallest increment, usually around .001-.0015". We got burned on this many time at places I worked when people collected data down to .0001" from a dgital caliper and then did designs off of that data, only to find the parts didn't fit because the measurements were inaccurate by .001" or more do to the measuring method. It is very easy to assume that a gauge is as accurate as it reads to, but that is often not the case. We would actually tape over the last digit in a lot digital displays, as they were not accurate anyway.

[avanti]

Originally Posted by booster

It does look like the 1500# gauge would give the best results. It would use the maximum amount of range on the dial, which always gives better resolution and guesstimation between lines.

Always be careful when you look at the digital gauges for any purpose. Often they have no better resolution or repeatability than the analogs, if they are low end stuff. A prime example is a digital caliper. Most dial ones read to .0005", and digital ones will read .0001" or even 00005" in some cases, but both style will have accuracy and repeatability considerably higher than the smallest increment, usually around .001-.0015". We got burned on this many time at places I worked when people collected data down to .0001" from a dgital caliper and then did designs off of that data, only to find the parts didn't fit because the measurements were inaccurate by .001" or more do to the measuring method. It is very easy to assume that a gauge is as accurate as it reads to, but that is often not the case. We would actually tape over the last digit in a lot digital displays, as they were not accurate anyway.

Yeah. Kind of like reporting SAT scores to three digits.

[booster]

Originally Posted by avanti

Yeah. Kind of like reporting SAT scores to three digits.

Lots of that kind of stuff going on, for sure.

Add to it the way a lot of meters and gauges are rated, and it gets even worse a lot of times. Many are rated as a % of full scale, which can be a huge error is you are measuring at the low end of the range. A 2% error pressure gauge doesn't sound all that bad, but when it is 2% of full scale on a 4000psi gauge, that is 80 psi. If you are measuring at 800psi, you are at 10% error of reading.

I really hate the ones that make it cryptic, so you don't even know what they really are. "one half of one percent of the least significant digit, plus or minus .05% of the range" type stuff.

I went through this routine when I was looking at the inductive pickup ammeter for our van. It is rated at 300 amps, which often would mean low accuracy when at very low readings, especially with inductive. I finally called and talked to about 5 different people who didn't have a clue, and finally got a tech who had actually tested on at the low end, who said that anything above 2 amps would be good to within 1 amp, which was good enough for us. When we are watching to shut off the coach charging from the engine, we usually do it in the 5-10 amp range.

[markopolo]

The 20psi gauge graduation on the 1500psi gauge would be better than the 50psi on my current gauge.

1500psi_.jpg

You'd easily be able to see 800psi or 820psi for example but also would be able to estimate 805, 810 & 815.

[booster]

What brand and source did you decide on for the gauge vendor? A quick look showed the cheapest ones on ebay, with others usually quite a bit higher. I think $17 for a 1500# gauge there.

I assume the ram has a 1/4" NPT thread? so that would be the what you would need on the gauge?

The good is that the gauge should always be moving up when in use, so you don't even have to worry about movement backlash in a cheap gauge.

[markopolo]

The gauge I have came from Northern Tool and cost $13.99 - Valley Instrument 2 1/2in. Stainless Steel Glycerin Gauge — 0-3000 PSI | Hydraulic Gauges| Northern Tool + Equipment

Looks like they have it at 1500 psi also: Valley Instrument 2 1/2in. Stainless Steel Glycerin Gauge — 0-1500 PSI | Hydraulic Gauges| Northern Tool + Equipment

I think is is this series: Valley Instrument 41 Series OEM Gauges (single scale) | Valley Instrument Service

The 3-2-3% accuracy seems typical at that price point.

[booster]

Thanks Marko. Don't know what happened when I searched Northern a while ago, as it all it came up with were the expensive ones.

[avanti]

Marko,
So, in your setup the tire is balanced on the ram on a piece of plywood? I guess that isn't too hard if you are jacking up the corner. I think it would be difficult on a drive-up setup.

I guess I could convert one of my wooden ramps into a scale if I were willing to plumb together three rams to form a sort of tripod. Still not horribly expensive, and it would be very easy to use.

[markopolo]

The drive on idea is pretty cool.

I just used a scrap piece of 1/2 ply at first. It was probably 6"x8" but, by about the second weighing it was bending pretty bad and starting to crack. I swapped it out for a piece 3/4" thick and that held up well. It was an odd sort of triangular shaped off cut that was nearby.

Something in the range of a 6x6, 6x8 or 8x8 square or rectangle should work. I wanted it large enough to not have any chance or damaging the tire but small enough to easily center it. The tire is not on it for long.

It was stable enough to bounce the corner gently by pushing on the bumper. I did that in case the ram piston was binding with friction supporting some of the weight.

The ram I got didn't have the hole on the top of the piston that the how to websites show even though it has the same part number. I raised the piston using compressed air to get started with filling it. The hydraulic oil did squirt out while working the piston back & forth so eye protection and gloves would be needed.

weigh scale.JPG

Ideally, I'll get a chance to dissemble the ram and confirm the diameter of the piston (that's inside the ram body). That's critical info. I'm not sure yet if I should make a tool to fit that round nut or use a punch and hammer.

[booster]

Having the hole in the top would be nice to pull it up, but not critical, I guess.

It looks like the locking ring in your pic is two slots, on on each side. If the piston is low enough just a piece of steel bar may work, turned with a crescent wrench.

If you know someone with bike tools, an old screw bottom bracket bearing adjuster locknut tool is made just to do that kind of slotted setup, and is adjustable for distance apart. I have one made by Var, but Park, Campagnolo, and others made them, also, so they are pretty common for semi-serious and up bikers to have on hand. A good pin wrench would also work, and they are also common bike tools as well as industrial applications.

[markopolo]

Your flat piece of steel idea would work. The groove on top of the piston would allow it.

[GeorgeRa]

Not to derail the hydraulic trend but using an electronic load sensor(s) could be another option. This sensor requires compression to work.
https://www.aliexpress.com/item/Radi...d-5f362756faa5

This is a tensile sensor, a simple platform hinged on one end pull the sensor down hanging on some kind of simple bridge. https://www.aliexpress.com/item/S-ty...5-612b0beda42e

Bathroom scales have usually 4 sensors in each corner but I have not seen sensors with more than 50 kg per sensor capacity.


edit: I found 4 load sensors type with capacity of 4 x 300kg = 2640 lbs and 4 sensors display. Sensor height is 7.5 mm. so total scale could be around 1 - 1.5 in. Smaller footprint would require thinner load plates. Perhaps 3/8" aluminum plates CNCed with water jet, total cost would still be more than a hydraulic scale but likely more portable and accurate.
https://www.aliexpress.com/item/75kg...87f94109&tpp=1

https://www.aliexpress.com/item/High...a-7923718495bc

[markopolo]

Maybe someone here will make an electronic scale

I'm still pretty amazed that for around $50 we can get the corner weights of our 9,000 lb + or - vans at home.

It is a somewhat physical job though with similar effort and mobility needed to that of putting a spare tire on. Drive on convenience would take this to the next level and allow more folks to do it.

[booster]

Stability would have to be a big issue for a drive, I think, due to the very small area of the ram and the base of both the hydaulic and electronic sensors. Using two of them with a plate would not help in one direction, so you would need 3 or 4 or them, running up the cost a lot.

I think for anyone who wants drive up, or even more stable setting it on blocks procedures, may want to look at doing it a bit differently.

I have seen a lot of places in the past procedures for adding a pressure gauge to the bottle jacks used on hydraulic presses to be able to know load being used. I have contemplated doing it to my cheapo 20 ton, but haven't gotten around to it. The good press we had a work had a gauge and it was a good feature, but the press cost 5X what mine did.

I have heard about being able to use a bottle jack as a porta-power pump by clamping the ram all the way up and then over filling it with oil. You could then use the pump to push fluid out an added hole. I have never seen one, so I don't know for sure it would work, though.

If you had a gauge on a bottle jack, you could have the jack in you wood, or metal ramps. Have a loose steel plate or 3/4" plywood on the top of the ramp and a hold for the ram to come through. You would need stops to get located though. Drive on, jack up, read pressure.

The more expensive, lower, neater system would be to use Marko's cylinder as it was designed to do, with porta-power pump. Again, build it into your ramp with a moveable plate, drive up, pump up, read. The Harbor Freight pump does not have a gauge,so you would have to add one. I have seen others that have the gauge.

Hydraulic Jack Hand Pump Manual Engine Lift Hoist Portable 22000lbs 10 Ton Red | eBay

[avanti]

Originally Posted by booster

If you had a gauge on a bottle jack, you could have the jack in you wood, or metal ramps. Have a loose steel plate or 3/4" plywood on the top of the ramp and a hold for the ram to come through. You would need stops to get located though. Drive on, jack up, read pressure.

I was picturing replacing the top layer of one of my wooden ramps with a layer that consisted of three rams holding up a metal plate. So, you would just drive up and read. The rams could be recessed into the lower layers of wood such that the plate would end up at the same height as the other ramps.

[booster]

Originally Posted by avanti

I was picturing replacing the top layer of one of my wooden ramps with a layer that consisted of three rams holding up a metal plate. So, you would just drive up and read. The rams could be recessed into the lower layers of wood such that the plate would end up at the same height as the other ramps.

Yep, same deal as I was thinking of. Hardest part would be getting the 3 gauges in there and easy to see, I think.

Add the pump to them and you could read remote and have them retracted while driving up.