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.

 

[Stomper]

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

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.

I will start there. Thanks

 

[tacticalturnip]

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.

Any chance you sell them?

 

[MtnViewRanch]

Any chance you sell them?

Both actually.

The orifice fittings are only in #6 oring boss-M/#6 JIC-M in straight or 45s or 90s.

The check valve for 3/8 British ports, #6 oring boss ports, and I have adaptors for #8 oring boss ports which raises the check valve higher off the cylinder ports.
The fittings that I have for the check valve are all for a #6 JIC hose connection.

I'm guessing you need something?

 

[tacticalturnip]

Both actually.

The orifice fittings are only in #6 oring boss-M/#6 JIC-M in straight or 45s or 90s.

The check valve for 3/8 British ports, #6 oring boss ports, and I have adaptors for #8 oring boss ports which raises the check valve higher off the cylinder ports.
The fittings that I have for the check valve are all for a #6 JIC hose connection.

I'm guessing you need something?

I'm thinking that I need the orifice fitting to slow my top link down and help fight gravity. The OP here seems to have problems similar to what I've had, he just knows enough about hydraulic to actually put it into words.

 

[MtnViewRanch]

I recommend that both ports have the orifice fittings. I know that just 1 on the rod end is supposed to do the job, but too many times in the past it has taken 2 to do the job right. So 2 it is from me each and every time.

Now I build the orifice into the actual port adaptor fittings so that no additional fittings are used that create additional connection points as well as taking up more room. But what I have may not work for your application.