electro-hydraulic oil pressure fluctuation

Eh oil, eh? Do you mean electro-hydraulic oil? (Oil used in hydraulic systems the flow-rate and direction of which is controlled by electro-hydraulic servo valves or something similar?

You say the pressure from one pump is unstable. Is the pressure from the other pump unstable also?

Do the pumps have their own built-in pressure regulator?

Is the pump pressure regulator external to the pump(s)?

Is there an accumulator in the system? If so, is it properly charged and are the block and bleed (isolation and drain) valves in the proper positions?

Is there some hydraulically-operated device which is also experiencing fluctuations in position or flow or pressure control?

Are you sure the pump suction is not plugged and has a "free" access to oil?

Are the Eh pump suctions pressurized by some upstream pump? If so, is the upstream pump working properly?
 
Eh oil, eh? Do you mean electro-hydraulic oil? (Oil used in hydraulic systems the flow-rate and direction of which is controlled by electro-hydraulic servo valves or something similar?

You say the pressure from one pump is unstable. Is the pressure from the other pump unstable also?

Do the pumps have their own built-in pressure regulator?

Is the pump pressure regulator external to the pump(s)?

Is there an accumulator in the system? If so, is it properly charged and are the block and bleed (isolation and drain) valves in the proper positions?

Is there some hydraulically-operated device which is also experiencing fluctuations in position or flow or pressure control?

Are you sure the pump suction is not plugged and has a "free" access to oil?

Are the Eh pump suctions pressurized by some upstream pump? If so, is the upstream pump working properly?
We have 4 nos of servovalves each for 4 governing valves.one pump pressure is stable.we have replaced all filters in line as well as oil in tank also replaced by fresh oil.individual pumps are having inbuilt presuure regulating cum flow control unit.we have tried stabilizing pressure by regulating by this inbuilt system but failed many times.actuator was also charged with n2 to adequate pressure.discharge side check valves have been checked.
 
I saw a similar problem once when the coupling between the pump and the electric motor was slipping and causing erratic pump discharge pressure and flow.

I have also encountered a similar problem when the flow path downstream of the pump had a problem that resulted in excessive flow through the pump and was tripping the pump's motor starter on over-current. Site personnel had bypassed the overload relay and the pump motor eventually burned out but prior to that the pump pressure and flow were unstable. The problem was eventually traced to an improperly adjusted relief valve which had failed and was allowing lots of oil to flow through the relief valve which caused the pump motor to draw excessive current and eventually burn out.

Since the problem is only with the output of one pump, the pump has an internal pressure/flow compensator and you have replaced the pump it with a new pump and built-in pressure/flow compensator are you sure the new compensator is properly adjusted?

Also, have you checked the current drawn by BOTH pump motors? The current drawn by the problem Pump's motor is probably unstable but it should be less than the motor nameplate value. If the current being drawn by the motor of the pump with the problem is higher (more) than motor nameplate value and less than the motor which is running normally the problem is probably an issue with excessive flow downstream of the pump.

Please write back to let us know what you find!
 
Intzar,

If you want help and you don't provide good information in the first post, you need to answer the questions which were asked of you. Even if you deem them irrelevant for whatever reason. We are not there. We can't see what you can see. We don't know what you know (or don't know). We don't--and can't--know what you've done to try to troubleshoot the problem, or what the results were. Unless you tell us. In this case it would be EXTREMELY helpful if you could post the P&ID for the Eh oil system so we could make recommendations.
 
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