hydraulic cylinder ram.

[henryhoover]

hi there. i have got a problem with a hydraulic lift at work. it is a simple machine for lifting steel bins to empty them. there is a motor and pump with a directional flow valve on it then there are two hoses to the cylinder(ram) one at the top and one at the bottom. when i lift a bin and empty it then go to set it down it seems to shudder and vibrate on the way down. i have been told they changed the pump and the cylinder but to no effect. also it only happens after emptying a bin not wqhen u operate it with no load on it. if any1 has any suggestions. i am an electrician with little knowledge of hydraulics so if some could help it would be great thanks

[Doug Hanson]

Check to see whether there is a load holding valve built into the cylinder. Lock valves, or PO checks do not like to operate smoothly. Sometimes instead of a lock valve, there will be a counterbalance valve, these arn't usually as violent but can chatter do to hysterisis. I assume you have ruled out mechanical binding?
Look for a cartridge valve in the base cap of your cylinder, or on a block attatched to your cylinder. If it is a counter balance valve, there will most likely be an adjustment screw on it, if it is a lock valve it will just be a hex head. Do not remove or adjust either without making sure that the load is blocked and cannot fall. Also there may be pressure trapped behined the valve, so be careful when removing.