Help with top link

[Stomper]

I installed a hydraulic top link in my Kubota L2501. It works great except for one thing. If I drop my box blade to the ground and move forward the top link will compress a couple inches before becoming solid. If I then adjust the top link to where I want it, it will be fine until I lift the box blade up and drop it again. I can actually move the top link in and out a few inches by hand. My thinking is there is air in the system and the top link is such a small volume that the air isn’t getting pumped through the system and into the return tank. Is this possible and if not What could be the problem here.

 

[CloverKnollFarms]

Does it have a check valve installed?

If you run the full length of the stroke a few times, there shouldn't be any air

 

[LD1]

How heavy is the toplink and what diameter cylinder is being used?

The weight of the box blade is trying to EXTEND the toplink cylinder. IF you have fully cycled the toplink in and out a few times with nothing attached (to purge out all the air), and it still does it.....it could be the following:

When you move your control valve to extend the toplink.....you are pumping fluid into the base end of the cylinder....and giving the oil from the rod side of the cylinder a free path back to tank/reservoir. With the weight of the box blade......gravity may be making the cylinder extend FASTER than your tractor can pump oil into the base end of the cylinder.....causing it to pull air into the system and resulting in the issue you see.

Most people use orifice/restrictor fittings on a toplink to slow down the movement of the cylinder. Did you do that on yours.

 

[CloverKnollFarms]

I use flow restrictors and mine with a .031” orifice and it has a built in check valve

 

[LD1]

The check valve just prevents it from drifting but wont stop gravity from acting faster than the pump when the thing is cycled. The check valve also prevents it from ever being used with float

 

[ericm979]

I installed a hydraulic top link in my Kubota L2501. It works great except for one thing. If I drop my box blade to the ground and move forward the top link will compress a couple inches before becoming solid. If I then adjust the top link to where I want it, it will be fine until I lift the box blade up and drop it again. I can actually move the top link in and out a few inches by hand. My thinking is there is air in the system and the top link is such a small volume that the air isn’t getting pumped through the system and into the return tank. Is this possible and if not What could be the problem here.

Mine does that too.

Run the link in and out a bunch of times before you use the box blade. That will get the air out.

 

[Stomper]

Does it have a check valve installed?

If you run the full length of the stroke a few times, there shouldn't be any air

It does not have a check valve but I have been researching them. For the top link would I need a single piloted check valve or a double piloted one.

 

[Stomper]

How heavy is the toplink and what diameter cylinder is being used?

The weight of the box blade is trying to EXTEND the toplink cylinder. IF you have fully cycled the toplink in and out a few times with nothing attached (to purge out all the air), and it still does it.....it could be the following:

When you move your control valve to extend the toplink.....you are pumping fluid into the base end of the cylinder....and giving the oil from the rod side of the cylinder a free path back to tank/reservoir. With the weight of the box blade......gravity may be making the cylinder extend FASTER than your tractor can pump oil into the base end of the cylinder.....causing it to pull air into the system and resulting in the issue you see.

Most people use orifice/restrictor fittings on a toplink to slow down the movement of the cylinder. Did you do that on yours.

I did not use an orifice restrictor but I will look into it. I am also looking into a piloted check valve but not sure if I need a double piloted one or a single piloted one for the top link. To test if this is the problem, could I just feather the top link valve slowly when I am extending the top link.

 

[Stomper]

I use flow restrictors and mine with a .031” orifice and it has a built in check valveView attachment 805947

Mine is just the cylinder but I am looking into the restrictor and the piloted check valve.

 

[MtnViewRanch]

I doubt that you will find a double pilot operated check valve that will go onto your cylinder like the typical off-the-shelf top link units have as pictured in post #4. Those take 3/8" British pipe thread and your ports are most likely #6 oring boss.
I recommend putting .031 orifice fittings on each port and your issue should be resolved.