Corner weight vs axle weights

[markopolo]

The pump idea is great but there's only 7/16" travel with the ram I have so I don't know if that could work. You can get rams with greater range of travel.

[avanti]

Originally Posted by booster

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.

I think we have different pictures in our heads.

I am picturing three of the same rams as Marko's. They would all be plumbed together via T fittings to a single gauge. There would be no pump or retraction involved.

[markopolo]

With a tripod would the multiplier be 3 x sq in? 6.75 for the ram I have? 500 psi gauge?

[markopolo]

Also, it might be difficult to get the air out of the tripod system. A pump might be needed.

[booster]

Originally Posted by avanti

I think we have different pictures in our heads.

I am picturing three of the same rams as Marko's. They would all be plumbed together via T fittings to a single gauge. There would be no pump or retraction involved.

That would work, but you would have to be very careful about air, as Marko mentioned, as well as be centered well.

[avanti]

Originally Posted by markopolo

With a tripod would the multiplier be 3 x sq in? 6.75 for the ram I have? 500 psi gauge?

Seems like it. I would think that three small plungers would be equivalent to one large one. I am way out of my field here, however. There is obviously an answer, though.

[avanti]

Originally Posted by booster

..as well as be centered well.

Does centering matter? Don't the three pressures sum to the correct answer no matter what?

[booster]

Originally Posted by avanti

Does centering matter? Don't the three pressures sum to the correct answer no matter what?

If the 3 weren't tied together, centering wouldn't be a big deal as you would just add them together. With them tied together, the fluid will be able to go to any or none of them when compressed, so if one had more weight, in might go to full down, with the other going up, which would mess up readings, I think. You would have the same issue with a pump on them, too, so using a single one is a definite simplifier there.

[avanti]

Originally Posted by booster

If the 3 weren't tied together, centering wouldn't be a big deal as you would just add them together. With them tied together, the fluid will be able to go to any or none of them when compressed, so if one had more weight, in might go to full down, with the other going up, which would mess up readings, I think. You would have the same issue with a pump on them, too, so using a single one is a definite simplifier there.

Hmmm...
You are certainly right that if any of them bottoms out you are in trouble (since the fluid wound no longer be the only thing supporting the load). However, it is less obvious to me that having one or more fully-up would cause any issue. I guess that initial conditions during oil-charging are critical. My intuition is that if you filled the system with all three plungers all the way up, there would be no way for any of them to bottom out.

But, as I said, I don't know what i am talking about.

[booster]

The issue with hydraulic or air cylinders swapping oil or air is extremely common in industrial equipment, and is why you very, very, rarely see either of them used in an application where they are not topped out and over pressured to hold them there, or have locked volume on both sides of the piston. It is also the reason many of us have separate fill to our airbags, as there is no way to level with them tied together. In the rare instances of "floating" rams, we would never tie them together unless they had individual check valves to them, that you could release to have them retract, or individual manual valves. I built a two cylinder setup for a coating machine head that was very close to what we are talking about here, except upside down. It was hydraulic cylinders similar to what we are talking about here, but larger at nearly 4" diameter, and stock it was sealed and non connected between them. Since the cylinders determined the coating head location when it was active, they had to be extremely consistent to about .001". Any tiny leak would mess up the locations and require a painfully long adding of oil and trying to get them even. I put a hand pump on that setup with manual valves (not check valves) to each cylinder, so they could be individually filled, then shut off, or if they were too full when setting, you could open the valve on it and then open the release on the pump to release fluid back into the reservoir. Our height setting went from hours to minutes with it on the pump.

I think you could do the same type of manual vales on a drive on setup, especially if you had a gauge on each, but you might get by with one gauge if you pump them to same pressure on at a time and made sure they moved without topping.

[booster]

Originally Posted by markopolo

The pump idea is great but there's only 7/16" travel with the ram I have so I don't know if that could work. You can get rams with greater range of travel.

Now you know why most of them have a bolt in the middle of the ram, so you can use it to fill the major part of you clearance before you pump them up. Bummer they took it out.

[avanti]

Check valves...
That gives me a real dirtball idea:

I wonder if one could build an almost-free version of this idea using automative brake cylinders from the junkyard. Almost free, of a good scale for this application, and comes with all the fittings and check valves one's heart desires.

Hmmm...

[markopolo]

In Canada, Princess Auto stores have a cheap 4 ton low profile ram on sale:

https://www.princessauto.com/en/deta...am/A-p1200037e

It is quite a bit smaller than the Harbor Freight 10 ton ram.

4ton.JPG

The design of it is different also. The O-ring that seals in the oil does so around the small diameter part of the piston. I measure that part to be a hair over 28mm on this 4-ton unit and that converts to approximately 0.96 sq in.

1000 psi on a gauge would convert to approximately 960 lbs if that is how this one works. I'll have to assemble it with a gauge and test it sometime to know for sure.

[booster]

That is pretty inexpensive, for sure, especially in US$.

I am surprised that they can get by with an oring seal for that much pressure. Usually, you would need a self activating lip seal with a backup ring for that. The pic in the earlier link looked to be a lip seal and backup.

Of course all this leads to the inevitable question of if you do have a fairly large difference in cross weight on an axle, what do you do besides trying to rearrange things a bit? I suppose you could bias the swaybar to transfer more of the weight, but I don't know it that is a good or bad idea. At least it would put the suspension back at the height on both sides that it was aligned at.

[markopolo]

Your description of the parts involved is more accurate than mine.

Both have similar sealing parts. Both appear to have O rings based on very close inspection and moving the O ring around etc. Both also have what appears to me to be a nylon seal washer. The difference between the two is that the seal on the Harbor Freight ram is split so that it can fit over the piston base. The seal on the Princess Auto ram is unbroken as it fits inside the nut (threaded collar). The Princess Auto ram has an additional O-ring where the nut (threaded collar) meets the base.

What part should I be measuring the diameter of to convert to sq in?

My guess is that it should be the piston on the Princess Auto ram because the seal doesn't move up and down with the piston. The seal effectively forms part of the cylinder base unit.

My guess is that it should be the cylinder on the Harbor Freight ram because the seal moves up and down with the piston. The seal effectively forms part of the piston.

I know it is a very small difference but thoughts & comments on this would be appreciated.

[booster]

Usually, you can get away with measuring either the bore of cylinder on the wet side of seal or the biggest part of the piston on the wet side, as the clearance is usually quite small. This is a single seal setup so they would likely need to guide a bit on both sides of the seal to keep it straight enough to seal well. If there are steps or grooves in the piston in the piston on the we side, they really don't matter as the net area of pressure toward the seal stays the same, you just get some plus or minus that balances. If the seal moves with the piston like this does, the bore will be a touch more accurate and if the seal in in the bore, with a smooth piston, the piston will be slightly more accurate.

The plastic ring, on split, one not, that you see is called a backing ring most of the time. It does not seal anything as such, as it is there to keep the o-ring from extruding into the gap between the piston and bore. Non split are the best, but can't by used in grooves, only on shoulders. Slit ones are usually used on grooves both on pistons or in bores, and normally will have some overlap by an angle or step on them so the have no big gap in them. The backing ring allows o-rings to be used at much higher pressure and still keep the benefit of an o-ring sealing when not under pressure. Loaded lip seals, which also seal statically are much more expensive than o-rings.

On the new ram, if the o-ring is on a shoulder, not in a groove, you will have to be careful if you pull the ram up by hand, as it might slide the o-ring down the piston. It might go right back under pressure, but might also roll or distort, so be aware you might see more settling or even a leak.

[markopolo]

Thanks for the help Booster. I'm going to use 2.26 sq in for the 10 ton Harbor Freight ram and .96 sq in for the 4 ton Princess Auto ram for the psi to lbs multipliers.

Here are the two pistons:

differences.JPG

Both are inverted T shaped.
The larger Harbor Freight ram piston has a nice snug fit in both the cylinder and the threaded collar. The Princess Auto ram piston fits nice and snug in the threaded collar but it is loose in the cylinder with something like a 1mm gap. Oil will flow past it.

As to how to use the info .......

Each corner, combined front, combined rear & total weight are all good to know.

You could shift gear around or carry or not carry water etc.

I thought of using the info to set tire pressures but it looks like I could go as low as 50 front and 60 rear - that would likely feel squishy..... 60 front and 70 rear might be a good balance between handling and comfort when not towing.

My van has 4 configurations:
1. Lightly loaded.
2. Loaded for camping.
3. Loaded to camping with cargo box and bikes on the rear.
4. Towing the travel trailer.

The front weight doesn't change much but the rear can vary quite a lot depending on the configuration.

[booster]

I had to go back and look again at the first pix. I had the idea that the primary seal was at the shoulder of the piston and moved with it, but that lower seal under the cap is really just to seal the threads, with the primary seal in the cap on the small part of the piston.

Kind of a funny design, as the bigger diameter on the piston doesn't really do anything for them like give higher force. It is really just a stop. The piston could be small all the way down.

Sounds like you are on the right path, and will have better data than any of the rest of us. I do think this is something that I will be addressing in the not too distant future, as it just makes sense to know, and it is relatively easy and inexpensive.

[avanti]

Originally Posted by markopolo

I'm going to use 2.26 sq in for the 10 ton Harbor Freight ram and .96 sq in for the 4 ton Princess Auto ram for the psi to lbs multipliers.

So, could you determine their relative sizes precisely by clamping them together in a vice (face to face) and measuring the pressure in each? I guess you would need two gauges.

Once you had an accurately-calibrated press, you could use this technique to calibrate others, no?

[markopolo]

Thank you - great idea - I tried it.

Unfortunately, there's a 56lb difference between the two with about 600 lbs of force in the vise. It's a light weight vise and that the max I could put on it. The bar was bending.

I suspect that I've introduced a preload when tightening the gauge. It was obvious on one as it registered 100 psi after torquing down the gauge. I redid that one but not the other one. The other possibility is that there's air in the system.

I'll work on them again sometime soon.