Hydraulic top link issues

[CCWKen]

Too much hose for too little cylinder will cause that. Compute the volume of each hose compared to the volume of the cylinder. If the hoses hold more you'll never get all the air out. The cylinder must be able to push any air completely through the valve and to the return line.

Added:
You really don't need more than 1/4" lines for a top cylinder. Generally, it's use is for minor changes in the length of the top link. That's one of the reasons I would never use full remotes to operate a TC. It should be separate with smaller hoses or have restrictors in the couplings. Don't "gorilla" the valve and it won't squeal. Too many think the control valve is only on or off.

 

[Leejohn]

Reread post 13

 

[pmsmechanic]

I could be wrong here. It wouldn't be the first time! I'm thinking you'll never get the air out the way the cylinder is situated. There are always going to be air pockets because the cylinder is laying on it's side. Take the cylinder off and hold the ports up while cycling so that the air can go out of the hoses. If air pockets are the problem that should solve it.

 

[LD1]

OVRSZD....

Do you have a restrictor on BOTH lines running to the cylinder.

If your problem is the same as the OP's, I am fairly confident saying that the issue is probably the cylinder trying to extend faster than it can fill with fluid. As has been mentioned before.

However, if you put on a PAIR of restrictors, not only does that slow the fluid leaving the cylinder, but it also slows it entering the cylinder as well.

When extending the toplink, you are pumping fluid into the base port of the cylinder, With a heavy implement, fluid can leave the rod side faster than its being made up on the base side. You need only ONE restrictor, on the rod side ONLY. That will slow down the fluid leaving the cylinder. If you have a restrictor on the base side as well, you are slowing the fluid trying to enter the cylinder, and you are back to square one. You want to fill the base end of the cylinder as fast as the restrictor on the rod side will let fluid out.

So try removing the restrictor on the base end and see where that gets you.

Another option, all though more pricy, would be to install adjustable flow controls like I have on mine, and dial it in to suit your needs.

 

[ovrszd]

OVRSZD....

Do you have a restrictor on BOTH lines running to the cylinder.

If your problem is the same as the OP's, I am fairly confident saying that the issue is probably the cylinder trying to extend faster than it can fill with fluid. As has been mentioned before.

However, if you put on a PAIR of restrictors, not only does that slow the fluid leaving the cylinder, but it also slows it entering the cylinder as well.

When extending the toplink, you are pumping fluid into the base port of the cylinder, With a heavy implement, fluid can leave the rod side faster than its being made up on the base side. You need only ONE restrictor, on the rod side ONLY. That will slow down the fluid leaving the cylinder. If you have a restrictor on the base side as well, you are slowing the fluid trying to enter the cylinder, and you are back to square one. You want to fill the base end of the cylinder as fast as the restrictor on the rod side will let fluid out.

So try removing the restrictor on the base end and see where that gets you.

Another option, all though more pricy, would be to install adjustable flow controls like I have on mine, and dial it in to suit your needs.

Yes, when I ran the restrictors it was on both ports.

I agree with your assessment. I'll try just one restrictor.

I'm concerned about throwing the system into relief. Although that may not happen with just one restrictor. Is that a concern?

I think my friend was implying the vacuumn created might cause suction in the tank port. This would allow air in if the port dumled above fluid level. Do you think that's possible?

As to removing air from a cylinder. Lots of opinio s about that. The idea that hoses need to be removed, cylinders need to be elevated or tilted, hose size needs changed, etc., just doesn't add up. I can show you larve implements that have many,many feet of hose and don't have a problem.

I am sure my cylinder has purged itself. I am also sure the OPs cylinder has purged.

I didn't post here to distract from the OP's issue, rather I posted to reinforce it. Him and I aren't the only operators that have experienced this.

We still need to try to clarify where this air is coming from?

Thanks for any offerings LD1. I'll play with the restrictor idea and report back.

 

[ovrszd]

Too much hose for too little cylinder will cause that. Compute the volume of each hose compared to the volume of the cylinder. If the hoses hold more you'll never get all the air out. The cylinder must be able to push any air completely through the valve and to the return line.

Added:
You really don't need more than 1/4" lines for a top cylinder. Generally, it's use is for minor changes in the length of the top link. That's one of the reasons I would never use full remotes to operate a TC. It should be separate with smaller hoses or have restrictors in the couplings. Don't "gorilla" the valve and it won't squeal. Too many think the control valve is only on or off.

I'm afraid this isn't completely true.

As to hoses affecting getting air out. How does a batwing brush cutter work? The hoses easily hold more volume than the rod end of the cylinder. I have replaced hoses on road graders that are 20ft long. Cycle the lever a couple times and the air is gone.

Depending on applications a top link cylinder is used for much more than minor changes. When running my brush cutter my top link is fully extended and fully collapsed many, many times and at the GPM flow rate of the tractor.

I'm not sure what "Gorilla" means? Engaging the valve by pulling/pushing the handle is how it's intended to be used. Feathering can be done if required. But certainly should not be a necessity.

I do not believe that operator error is the OP's problem, nor mine.

I'll try to play with restrictors today and report the progress.

I pull a 5yd clam shell scraper with my Kubota. It has two large cylinders. I raise/lower it at full capacity of the valve. I never have "air in the system" problems and I'm positive it moves oil at a much higher rate and with much more capacity than my top link.

Again, hoping we can find a solution for anyone suffering with this problem.

 

[pmsmechanic]

You've got close to half a cylinder full of air that you need to do something with before any of your other ideas will do any good.

 

[LD1]

Yes, when I ran the restrictors it was on both ports.



I think my friend was implying the vacuumn created might cause suction in the tank port. This would allow air in if the port dumled above fluid level. Do you think that's possible?

Not likely. Draw out your system and flow diagram and you will see.

When the cylinder is extending, fluid is expelling out the rod side port, back though the valve, and into the sump.....weather above or below the fluid level.

Fluid is being pumped from your pump through your valve and trying to fill the base side of the cylinder. Problem is it cannot keep up with how fast fluid is expelling out the other side as a result of gravity. So the cylinder will pull a significant vacuum. Which will pull air in. Which can come from any number of places. If you were to take a bucket of oil and draw a vacuum on it, you would be surprised at all the little bubbles it pulls out. Vacuum will "lower" the boiling point of anything. It could also be sucking air in around the pump shaft seal. Its designed to seal pressure, from the inside out...not a vacuum.

But back to drawing air from the return being above fluid level.....I say unlikely because you are returning fluid as fast as the hoses will allow. It would be like trying to draw air back through a garden hose in the opposite direction the fluid is traveling.

 

[ovrszd]

Not likely. Draw out your system and flow diagram and you will see.

When the cylinder is extending, fluid is expelling out the rod side port, back though the valve, and into the sump.....weather above or below the fluid level.

Fluid is being pumped from your pump through your valve and trying to fill the base side of the cylinder. Problem is it cannot keep up with how fast fluid is expelling out the other side as a result of gravity. So the cylinder will pull a significant vacuum. Which will pull air in. Which can come from any number of places. If you were to take a bucket of oil and draw a vacuum on it, you would be surprised at all the little bubbles it pulls out. Vacuum will "lower" the boiling point of anything. It could also be sucking air in around the pump shaft seal. Its designed to seal pressure, from the inside out...not a vacuum.

But back to drawing air from the return being above fluid level.....I say unlikely because you are returning fluid as fast as the hoses will allow. It would be like trying to draw air back through a garden hose in the opposite direction the fluid is traveling.

Yep, makes sense.

 

[ovrszd]

Update.

I went to the farm, cranked up the Kubota, installed the BB. Ran the Top Link cylinder full in/full out several times. Extended the cylinder and then lowered the BB. The rear blade of the BB hits the ground first under this circumstance. Without activating a lever my top link cylinder would retract until the BB was able to sit level on the ground. Approximately 4" of cylinder movement. I recycled the cylinder several more times and then did it again. Same result, cylinder would retract.

I uncoupled the rod end hose. Held it up in the air above everything else and removed the quick coupler. The hose was completely full of oil. I installed one of the restrictors I had bought from Brian. Not sure what diameter hole it has, maybe he can chime in with the specs.

Recoupled the hose, lifted the BB and fully retracted and extended the cylinder several times. Extended all the way and sat the BB down on the ground again. No compression at all.

I then removed the top link cylinder from the tractor and put on the top link cylinder from the Ford. Same diameter cylinder, just an 1" shorter. Cycled several times and sat the BB down on the ground. Cylinder retracted.

Uncoupled the rod end hose from the tractor, held it high in the air and removed the quick coupler. Same result, hose was full of oil. Added the second restrictor I got from Brian. Repeated the test. No compression at all.

One more thing. The Ford had never displayed this problem, only the Kubota. According to the tractordata.com the Ford is an open center system with 7.7gpm flow rate at 2500psi. The Kubota is an open center system with 17gpm flow rate, pressure not posted.


I believe this has solved my problem. It was too cold and snowy to spend any time trying it out in real world scenarios. I'll save that test for better days.

My curiosity is peaked as to where the air was coming from? Probably never know definitively. Obviously the Kubota's increased flow rate is causing this problem? I've got 3 rear remotes on the Kubota and had previously tried the top link cylinder on each of them with the same results. To me that eliminated a specific problem in one valve?

Hope some part of this is helpful to the OP.

Just for visual effects, here's a pic of the Kubota's setup and the Ford. 3.5" diameter cylinders.