We have Electro Hydraulic system for Steam turbine control valves consisting of two Parker PV15 axial piston Oil Pump where one pump is kept running and other remains on standby condition. Normally the pressure on the pump delivery remains at 140 bar. A week ago, suddenly one pump's delivery pressure reduced to 100 bar and standby one started due to interlocking system. 6 days later, second one's pressure also got reduced and Steam Turbine Tripped. Now we are trying to build up EH Oil Pressure by starting pump. But after pressure increases upto 90 bar, it suddenly gets reduced to 2 or 3 bar although pump is running and stays on that. If we stop the motor and start again, same thing happen (Pressure increases upto 90 bar and suddenly drops to 2-3 bar). A sudden 'ping' sound occurs during pressure drop. Pressure drop happens within second. Both the pump shows same phenomenon. Only difference being for one pump pressure increases upto 90 bar and for another one, it increases upto 65 bar
We have changed the delivery filter. There is a relief valve, non return valve and isolation valve after pump delivery. We have checked Relief valve(Pilot operated) and found no abnormalities. We even interchanged the spring of the relief valve with a solid bar to ensure that oil is not drained through relief valve. But the same phenomenon occurs again and again. We disassembled the pump and found no abnormality.
What can be done now? Hoping for some suggestion.
We have changed the delivery filter. There is a relief valve, non return valve and isolation valve after pump delivery. We have checked Relief valve(Pilot operated) and found no abnormalities. We even interchanged the spring of the relief valve with a solid bar to ensure that oil is not drained through relief valve. But the same phenomenon occurs again and again. We disassembled the pump and found no abnormality.
What can be done now? Hoping for some suggestion.