Balancing tandem cylinders?

[RickB]

If you were to disconnect the rod ends off your loader arms, and cause the cyl to extend, one of the cyl may lag somewhat because of seals, or is just tighter, that would be normal. They both will finally push out to max. .

True.

There are balance circuits for cyls that read the pressure , and other things like cyl position, etc. If the cyl ends are connected to the same ref plate, and rod end is pushing on the same reference wedge /plate, the force should double with the same resistance. .

Untrue. Force will remain the same, not double if resistance is constant. Fact of the matter is, system pressure will be lower with two cyllinders overcoming resistance equal to what was present when only one cylinder was used. Sufficient force is developed to overcome resistance, no more.

One way to determine that, would be to put a gage on each cyl base end port, and push against something solid. This is assuming that the cyls are equal. If they are not equal, as in one cyl is leaking internally, then that cyl will show less pressure, but the force will add up with whatever pressure is available.

If the forces does not add up, to be twice the single rated force, that tells you that one cyl is better than the other. .

Also untrue and we have discussed this before. A leaking cylinder will limit pressure throughout the work port circuit, not simply in the branch feeding that leaking cylinder. If your 'theory' were valid, every loader boom with a single leaking piston seal would instantly be twisted by the vastly unequal pressures exerted by the leaking and non-leaking cylinders. It simply does not work this way when a leaking and non-leaking cylinder are fed by a common supply. The pressure differences are small and dictated by any flow limitations in the lines feeding the cylinders.

Just tee in two gages to test this theory.

This is also a good way to match up a pair of cyl.

Had you ever actually performed this test, J_J, you would have not posted half of this.

 

[DiskDoctr]

Years ago, when I first started seeing hydraulic wood splitters becoming more popular, many were made this way with 2 smaller cylinders versus 1 larger one. Secure both base end and rod end to the same fixed attaching points and plumb cylinders in parralel. Either mount them side by side or one on top of the other. Stacking them veritically, on top of each other, would allow having a taller push block and reduce binding of the block on the slide.

Brilliant!!!

Stacking close together vertically could cause a little twisting, which should be easily held in check by the guide grooves on the sides of the push block. MUCH better than a side to side twist. Likely will never be a problem.

I have a lead on a large cylinder, but don't know the condition of it yet. If that doesn't pan out, I'll be looking at stacking 2 cylinders.

Thanks to all for the input and ideas. I am used to working on hydraulic systems when they need it, but designing is a bit different. I know some parts well, other areas I have some gaps

- JC

 

[J_J]

Perhaps potential force would be more appropriate.

You can determine max force with a constant pressure, knowing bore size, rod size on a cyl, and pump pressure. So, if the pressure isn't available to the weak cyl, or leaks off, then the cyl can not develop the max pressure.



4 in cyl, 2 in rod, 3000 psi = 37,699 lbs
---------------2500 psi = 31,416 lbs Leaking seals.


Yes I know the pressure from the leaking cyl will decrease the available pressure with two cyl in parallel. That just reduces the potential force.

So are you saying, that I can not determine if a cyl can develop and maintain a certain force with a certain pressure.

Using two new cyl, and applying pump pressure to each cyl with gage installed, I should be able to determine which cyl will develop the most force based on the pressure holding capability.

I believe the weak cyl only developing 2500 psi used above, indicates the potential force lost because of leaking seals.

And yes, I can see a a fully loaded bucket rated for 2000 lbs using two cyl, and one of the cyl were to fail, the lift arms could twist. What happens when a cyl blows the seals on a BH, or leaks really bad.

True/untrue, whatever.

Perhaps you can find a couple of cyl and do a test and determine if they are equal or unequal and the difference and provide the results.

I wish I had the luxury to do all the test I would like to do.

 

[RickB]

Perhaps potential force would be more appropriate.

You can determine max force with a constant pressure, knowing bore size, rod size on a cyl, and pump pressure. So, if the pressure isn't available to the weak cyl, or leaks off, then the cyl can not develop the max pressure.



4 in cyl, 2 in rod, 3000 psi = 37,699 lbs
---------------2500 psi = 31,416 lbs Leaking seals.


Yes I know the pressure from the leaking cyl will decrease the available pressure with two cyl in parallel. That just reduces the potential force.

So are you saying, that I can not determine if a cyl can develop and maintain a certain force with a certain pressure.

Using two new cyl, and applying pump pressure to each cyl with gage installed, I should be able to determine which cyl will develop the most force based on the pressure holding capability.

I believe the weak cyl only developing 2500 psi used above, indicates the potential force lost because of leaking seals.

And yes, I can see a a fully loaded bucket rated for 2000 lbs using two cyl, and one of the cyl were to fail, the lift arms could twist. What happens when a cyl blows the seals on a BH, or leaks really bad.

True/untrue, whatever.

Perhaps you can find a couple of cyl and do a test and determine if they are equal or unequal and the difference and provide the results.

I wish I had the luxury to do all the test I would like to do.

Keyboard diarrhea. Your lack of knowledge concerning cylinders plumbed in parallel coupled with your insistance on broadcasting that deficiency is amazing.

 

[glastron23]

Rickb..... good one..... isn't there some law of fluids that say something like pressure in a confined space is equal in all directions??/ i think his name was pastal.....paxall,,, patcal..... OH PASCAL .... thats it.....

 

[N8ghz]

The first log splitter I built was with (2) indentical Miller cylinders, 3.25"x24".
I did nothing but run each cylinder hose from a standard log splitter valve into a T and from it to each cylinder. Both cylinders are mounted the same way, and the rod-ends connect to the wedge the same. It is still in use and I have never saw any reason to concern myself with any balancing...the fluid does that normally.


As to your idea of using a triangle mount for your rod-ends, with a rod on each of 2 points and the single point on your splitter wedge/plate....I'd not do that. Mount them ridgidly and indentically measured. With the triangle thingy it would invite and allow movement between the cylinders side to side or up/down. The scenario would aggravate if say....one side of you ram slide got dirt,etc. on it and the other side was slicker than a cat's *** and your slide wobbles. It would work, but would be alot better if the cylinders always tracked the same with ridgid mounting points between base & ram.

 

[MHarryE]

Combine grain heads we used a phased set. One side double acting with the rod end having the same displacement per inch of travel as the slave at the other end. Master also had a phasing hole so when it reached the end of the stroke oil flowed directly through to the rod end and thus to the slave. Also had a bleed screw at the top of the slave so we could bleed air from the slave. In the field if they ever got a bit out of phase raise all the way to the top and the oil would flow through so both cylinders are back in phase. Very low cost way of controlling something you must keep level but requires cylinders designed for the job - displacements, phasing bypass and air bleed.

 

[DJNebraska]

There are two different ways to split hydraulic flow front a single source. One solution is a "gear type" flow divider and the other is a "spool type."

Gear Type Flow Dividers

Spool Type Flow Dividers

Keep in mind that a divider that splits input hydraulic flow exactly 50% - 50% does NOT exist. There are high-end dividers that will get you within 1.5% - 2% inaccuracy, however.

As mentioned, the best way is to mechanically link the two cylinders with a rigid frame so that a flow divider is not needed.

 

[DiskDoctr]

I can see the rigid mounting vertically being the better option here. The cylinders will "resync" with each retraction, so shouldn't have a cumulative out of sync (grown error).

I have learned some more about flow dividers, though Thanks to all for the info!

- JC