Balancing Hydraulic Cylinders on a Log Loader

[jteneyck]

I've been a member here for several years, but haven't participated lately.  Anyway, I would appreciate your help with how to balance the cylinders on a hydraulic log loader I'm designing for my currently manual trailer mounted mill.  Currently, I load logs up ramps with a single line electric winch.  It works well with round logs of consistent diameter, but taper, flat spots, or knobs can cause one end to slip and slide back unless I'm there to keep it even.  It's not too much of a problem when I have help, but when I'm working alone, which is most of the time, things can go wrong in a hurry.  I've thought about using two winches, and still might, but a hydraulic log loader would seem to inherently eliminate the problem, unless I'm missing something.  

It's seems obvious that the two hydraulic cylinders need to move together despite any load imbalance, but what's the easiest, cost effective, and reliable way to do that?  Tying the loading arms together rigidly would help, but likely isn't enough.  For those of you who have built your own log loader how did you make the cylinders move in unison?  Photos, parts, etc. greatly appreciated.  Thanks in advance.  John 

[2308500]

i think a torque tube from one arm to the other would be the most cost effective solution.

[Satamax]

If i'm not too daft. Hook the two cylinders in parallel on the same line. And that should be enough.

Or is it in series?  ;D Shaft side of first cylinder pushing its oil into eye side of cylinder two. I can't remember how it is plumbed thought. 

[tacks Y]

They make a valve for this, I think a balance valve. Gives equal flow to each cly. There is one on my log stops so they travel together.

[2308500]

not too familiar with this type of unit but from what i see the torque tub looks like the way i would go.  if the resting point of both reaction arms is uneven, the torque tube way would allow for equalization whereas the equalization valve may force you to block up one end or dig down for the other.  But i'm probably wrong

[Joe Hillmann]

A Y shaped chain will keep the log rolling up straight wit a single winch attached to it.

[barbender]

My Woodmizer loader has a torque tube between the two loading arms.

[mike_belben]

There is nothing to be concerned about here.. You just come out of your valve port A, run to a point central to the cylinders, to a TEE fitting then one hose to each cylinder fitting on bottom.  Now another hose from port B to another tee that goes to the tops.  In parallel the cylinders will move in unison.


A round tube between the loader arms will resist torsion very well.  Larger diameter is more important than larger thickness.  3" exhaust pipe or conduit will probably take 100hp in torsion.  I use conduit, handrail, exhaust and sched 40 scraps constantly for torsional resistance.  It only need be thick enough to avoid denting.. If you even care about that part.  In a driveshaft certainly denting and bending matter but they need to be light to balance. 

[jteneyck]

Thanks for the input, all.  Joe, the Y chain is a potential option if I re-design the winch mount to move the winch further back so the chain doesn't reach the winch before the log is up on the mill.  

Mike, that makes sense in a perfect world, but if the load is not equal on both sides I think that torque tube is going to be mandatory to keep the arms moving up uniformly.  But if that is how Woodmizer and others are doing it it must be OK.  

Another idea I think is to use 2 valves and control each side independently.  

Thanks again.  

John  

[moodnacreek]

I have a log deck that is stationary but I built a loader that lifts and dumps lumber. It has two cylinders and the arms are welded to a thick 'torque tube' as others have mentioned.

[Magicman]

Balancing the cylinders is necessary because each of my loader cylinders have a velocity fuse to protect against the loader falling in the event of a catastrophic failure of a hydraulic hose, etc.  An out of balance load can sometime cause one of these fuses to operate and lock the loader arms.  Slightly raising the loader will reset the fuse and then the loader arms can be slowly lowered.

On a diy build I certainly would incorporate velocity fuses for safety.

[mike_belben]

Youre overthinking the hydraulics john.  Look at the next 500 wheel loaders you see and try to find one that has issues with raising an engine thats chained to one side of the bucket.  They all have one valve and 2 parallel lift cylinders.  


Magicman's 'velocity fuses' are probably whats commonly called "load checks" by hydraulic manufacturers.  They use checkballs to block the cylinder descent unless first unlocked by fluid pressure from you stroking the spool lever to go downward.  They prevent creeping/leaking down too as long as the rod seals are good. 

[YellowHammer]

Hydraulics work off pressure and flow. Pressure is pressure, pounds per square inch, and by its very nature is balanced.  Split the hydraulic feed line with a T and plumb to each cylinder, which all of course have to be the same diameter, to have an equal rod force based on pressure.  As the load lifts, equal pressure is fed to each cylinder piston face and so equal force is generated on each rod, no matter how many pistons are in the circuit. The torque tube is there to equalize the force if there is a load imbalance, to help transfer the load from one arm to both arms.    

When designing the system it is imperative that the arms be strong enough to completely stall a single or both pistons at maximum delivered pressure.  For example, front end tractor loader arms are designed to not bend if the load is so heavy that it stalls the hydraulics, even if the bucket stalls on one side, and releases the pressure relief valve.  If the arms are too weak, they will bend.  Just like a front end loader who can hook a root ball in one corner tooth and stall the hydraulics without bending its loader arms, so should the sawmill log loader arms and torque tube assembly be that strong.  

The velocity valves are in reality flow control valves, based on differential pressure on either side of an orifice.  If a flow rate is exceeded for any reason, be it a heavy unbalanced load, or generally a hydraulic line rupture, they will close and hold line pressure.  They do this by acting if there is a significant pressure differential across a small orifice, caused by excessive flow, and having a spring loaded poppet close.  This is an exceptional safety feature on loader arms because if one hydraulic line breaks, the heavy load will drop very rapidly causing a massive increase in flow rate of the hydraulic fluid as it shoots out the break.  Any loaded cylinder in the system will drop and push its fluid out at a very high flow rate, causing a differential pressure across the orifice, hence the name velocity valve.  As the hydraulic flow rate exceeds the maximum open rated flow rate of the valve, it will close and hold pressure, keeping the fluid in the cylinder and the load suspended.  My velocity valves in my log loader are rated at just over 7 gallons per minute, if I remember correctly, which is just a little higher flow rate than the hydraulic pump. The flow capacity is stamped on the side of valve.  

[Dave Shepard]

This is the Wood-Mizer loading arm setup. The feet on the loading arms move independently so that they are both taking equal parts of the load, even if they are on uneven ground. 



 

[tmbrcruiser]

I built my own log deck and piped hydraulics from the mill. A flow divider will balance the lift and keep the timing equal on both cylinders. Works like a dream and was not costly.

[jteneyck]

You could write volumes about what I don't know about hydraulics so thanks for the additional help.  

John  

[711ac]

Look for a "rotary flow divider" I had a link posted but edited it to this. There not an advertiser here but I've unintentionally got into trouble doing this (links) before and I respect this rule. It's a little over $200.

[richhiway]

Use one cylinder in the center.

[Dave Shepard]

If the leader arms are attached to each other like in my photo, then you don't need to balance the cylinders. If the loader arms are not attached to each other, then there is nothing you can do to make them go up evenly unless they originate from a fixed location on the mill.