640 Hydraulic Lift?

[Clay8Ns]

Okay Guy"s!!I had to change the relief valve on the bottom of the housing and now the pressure is 2200PSI.Still won"t lift.No visible leaks inside.Removed the lift cover and put it in a vise with lift arms looking up.When I put air to it with the lift handle in the down position the piston will move.When I put air to it with the lift handle in the up position the piston won"t move.Also when the piston is fully extended and the lift handle is in the up position the arms will stay up and when it is lowered the arms will fall.Do you think the unloading valve is bad?
Thanks to all of you for your advice!It is always good!!

 

[awhtx]

You've got it where it's easy to replace all of the o-rings on the piston and unloading valve so I'd go ahead and go through it completely. I don't think the unloading valve can go bad- just replace the o-ring on it.