PLC 5 hydrulic Problem

we have a machine that will not seem to hold position, we have replaced the tempo, cabling hydralic cylender, servo valve. And right when you turn the hydralics on it seems to do a lot of moving around like it can not find and hold position. after a while sometimes it seems to steady out and run just fine. Any ideas will help thanks

I always start will the hydraulic pressure.
Check the pump pressure, filters, and accumulator pressure.
Peter N. will probably have your best advice.
More info might help too.
Please excuse my terse reply - My 2 year old is demanding some attention.
Steve.

How old is the system. There are two very different tacts to take based on whether it is new equipment or old equipment.

I'm guessing there is some sort of tuning in this system? Could it be possible that someone played with it?

Has the friction in the system changed?

Does the valve have a nulling requirement?

I have told you guys today that I hate problems like this?

I would like to know if the system hold position after the system warms up. Parts wear, tuning changes some times a little adjustment is needed. If the problem was with the valve it would tend to have a null or bias that is one one side so the positions would tend to be always positive or always negative until the integrator winds up to adjust for the valve bias.

The other questions were good too. We need more info.

Water, dirt in system, non contaminated oil? Did not see any mention of replacing filters -- uhhh you do have filters?? Oil up to temp, leaky valves, bad electrical connections??

Dan Bentler

When you turn off the hyd how far does the cylinder move? If the controller is still trying to hold position then it can build up a lot of command then when the hyd comes on it can jump. You should be able to get online with the controller or just put a meter on the command signal to the valve and see this. A mechanical system could be getting worn letting it move some. Does the system have blocking valves? What else is in the hyd system. Counter balance valve could cause this as well.

Tell us more.