S220 variable flow is jerky

[nirias]

The variable flow on my S220 has developed a problem recently where the variable flow surges when released. So for example, while slowly opening the jaws on my grapple, the jaws move nice and smooth but when I release the variable flow switch the jaws jump open another several inches. The same thing happens when slowly closing the grapple. The lurch is violent enough that there is a slamming sound from the grapple, as if there is an extra pulse of oil flowing at the maximum rate. The same function on this grapple used to move and stop moving very smoothly. Now it is jerky enough that it appears there is a spastic at the controls of the machine. Any idea where to start in diagnosing this?

 

[Tazza]

I assume its only one direction? close? It could be a sticky valve stem. If you lift the cab and swap the stems, see if the problem moves to the open function.
People say the stems can't be repaired, thats not true. If its sticky you can pull them apart and clean them out. I have done it twice with good results. If the clean doesn't work, you will need a new one. The stems will un-screw. Hold the part with the O rings in a vice with soft jaws then use a spanner on the hex and un-screw it. Give it a clean with air and solvent, oil up and re-assemble.

 

[nirias]

I assume its only one direction? close? It could be a sticky valve stem. If you lift the cab and swap the stems, see if the problem moves to the open function.
People say the stems can't be repaired, thats not true. If its sticky you can pull them apart and clean them out. I have done it twice with good results. If the clean doesn't work, you will need a new one. The stems will un-screw. Hold the part with the O rings in a vice with soft jaws then use a spanner on the hex and un-screw it. Give it a clean with air and solvent, oil up and re-assemble.

I am seeing this problem in both directions. Following the intended slow flow in either direction, there is a significant surge in the same direction when the switch on the joystick is released. It is as if it opens the flow wide open for a small fraction of a second and then slams the valve shut.

 

[nirias]

I am seeing this problem in both directions. Following the intended slow flow in either direction, there is a significant surge in the same direction when the switch on the joystick is released. It is as if it opens the flow wide open for a small fraction of a second and then slams the valve shut.

This problem mysteriously went away. I hope it doesnt return.