Fr. 9E Hydraulic Oil discharge pr trouble


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GE Fr. 9E 9171 main hydraulic oil pressure get change suddenly without change in parameter which can effect pump performance, line traced no leakage found. I use VR21 for pressure control, but no change. Finally, I twisted pump pressure compensator to increase the discharge pr from 93 kg/cm2 to 100 kg/cm2. After 24 hrs it again dropped to 92 kg/cm2, again without any reason. Everything is fine with auxiliary hydraulic pump (104 kg/cm2).
I don't have a set of piping schematic drawings to review today, but if you are referring to the variable pressure *relief* valve at the manifold block where the outputs from the Main and Aux Hyd Pumps are joined together, the function of that valve is *NOT* to control pressure or to maintain a pressure setpoint. It's function is to protect the system in the event the pressure compensator on the the Hyd Pump fails. If you are using VR21 to control the pump output pressure, then you are flowing too much oil through the hydraulic pump(s) and through the relief valve(s).

One needs to set the relief valve by adjusting the pump pressure compensator pump to increase the pressure to the point that the relief valve starts relieving, set the relief valve to the proper pressure (per the value in the Device Summary, which should be higher than the Hyd. System Pressure, which is to be set using the pressure compensator on the pump), and then reduce the pressure compensator setting to the hydraulic system pressure setting for the pump listed in the Device Summary. This needs to be done for both pumps.

I don't know how old your unit is or how long the relief valve has been used to control hydraulic system pressure, but the hydraulic system on a GE-design heavy duty gas turbine is basically a static system, and there is only flow when there is a position change required. If the relief valve is being used to control pressure, there is much too much flow through the pump, and that could be creating a problem for the pump which has caused it to begin to fail.

Even if the pump isn't very old, all mechanical devices do eventually fail or require maintenance.