Balancing tandem cylinders?

[DiskDoctr]

How do you tie two smaller cylinders together, one one each end of a pivot bar, so they stay synchronized and balanced?

I want to provide more force than one cylinder provides, so I am thinking how to connect 2 cylinders to the same push mechanism.

Think a powerful and fast splitter or press with two cylinders that must push and pull in a perfectly balanced speed. They would be matched cylinders of the exact same size, model and type.

I have various cylinders and such available. No sense buying a large, expensive cylinder if I can use two smaller ones I may have around

Any ideas?

- JC

 

[glastron23]

the problem is #1 how accurate do you have to be #2 now much money don't you want to spend????
for #1 try this Divider, Flow, 2.4-5 GPM - Hydraulic Flow Dividers - Hydraulic System Components - 4F660 : Grainger Industrial Supply
for #2 try this HydraForce Hydraulic Flow Control Cartridge Valves
Jim

 

[tshep]

"one one each end of a pivot bar" and "splitter or press with two cylinders that must push and pull in a perfectly balanced speed" sound like 2 different things.

Each end of a pivot sounds like opposite travel and press sounds like same travel.

For simple press, I think they could just be plumbed in parallel.
That's how my FEL lift arms are - the mount/mechanism kinda' makes up for any temporary differences. I would think mounting both on a single extra long bolt (each end) would just double the force area and any difference between the 2 would quickly average out through the circuit flows.

 

[glastron23]

just what are you trying to do here?? just pushing on a splitter plate or trying to push 2 cylinders to lift a boom.

 

[mrmikey]

Don't know what type of application you're trying to design but there's another alternative, depending on how much money you want to spend.
See if you can find two cylinders that the volume on the rod end of one equals the volume of the barrell end of the other. After the rod end of one and barrell end of the other cylinder is filled with oil they're connected with hydraulic hose and purged of any air. Then the opposite end of each cylinder is then plumbed, one to each working port of the valve.

This will work as a similar system is used on a side dump salt spreader body to make sure the side went up evenly. Previously a flow divinder was used but going this route is cheaper as they're isn't any extra parts required. There are disadvantages tho, it's imperative to remove all the air as air will compress throwing off the syncing of the stroke. Also it's a pain to fill up without getting air in the system.

Afried of mine has the same setup on a bend brake he had built to make sure the blade moved evenly without going into the expense of fancy hydraulic valves.....Mike

 

[Brad_Blazer]

2 identical cylinders plumbed in parallel will put out the same force. The mechanism just needs a little rigidity to keep them synchronized. Almost every loader uses this setup.

 

[DiskDoctr]

I'm thinking about for the log splitter of a firewood processor. 40-60 ton.

Picture a triangle shape with a pin on each point. One cylinder is attached to each of 2 points, with the flat side of the triangle going between the cylinders and the other point faces away from the cylinders and attaches to the push plate of the splitter.

I was thinking about using two smaller cylinders, combining through this mount to push the splitter plate with a combined force. Balancing them would be to prevent binding and uneven pushing.

The balancing wouldn't have to be incredibly accurate, just enough to prevent binding

- JC

 

[glastron23]

Diskdoc.. if you are going to attach the base of the cylinders to a common point and the rod ends to a common point then synchronization is not all that important. The hydraulics will level themselves out. Jim

 

[SSdoxie]

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.

 

[J_J]

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.

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.

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.

Just tee in two gages to test this theory.

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

 

[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