BHEL Gas Turbine Frame-V machine have problem of MOP discharge pressure and Trip Oil pressure gradually drop.
MOP discharge pressure dropped up to 3.9 Kg/cm2 (Normal Pressure 4.5 Kg/cm2), and Trip Oil pressure dropped up to 3.3 Kg/cm2 (Normal pressure 4.3 Kg/cm2). Lube oil header pressure is maintained 1.9 Kg/cm2.
Following activity are carried out to increase the trip oil & MOP discharge pressure.
1. VR1 Tightened fully but no improvement.
2. MOP discharge pressure gauge isolation valve OL-5 isolated to suspecting any drain passing. But no improvement.
We doubted on VPR-1 so started AOP in manual mode and observed trip oil pressure became 4.3 Kg/cm2. So VPR-1 Ruled out.
We could not identify the problem why trip oil & MOP discharge pressure is coming down. Either MOP itself problem or any other checks we have to do.
The Subject line of this thread states a gradual drop in pressures, but there are not details in the post about how long this drop in pressure has been going on. A week? A month? Three months?
The Main L.O. Pump is generally a positive displacement pump inside the Accessory Gear Box. And, the pressure is controlled by VR-1 (yes--a relief valve is being used to control pressure; but it's sized (or should be) for the application, and this has been the method of limiting the positive displacement Main L.O. Pump pressure for decades).
I would suggest that if you made an adjustment to VR-1 and didn't see any change in pressure, there is a problem with VR-1. Or, that the Main L.O. Pump is failing and no adjustment of a working VR-1 can compensate for the drop in Main L.O. Pump flow/pressure.
Or, that somewhere in the L.O. Reservoir there is a pipe connection on the Main L.O. Pump discharge line upstream of VPR-1 that is leaking.
VPR-1 is usually used to control L.O. Bearing Header pressure, not Trip Oil pressure (refer to the L.O. System P&ID). L.O. Pump discharge pressure (Main or Auxiliary) is used to supply the Trip Oil system through a fixed orifice--upstream of VPR-1.
Starting the Aux. L.O. Pump with the Main L.O. Pump running adds the Aux. L.O. Pump discharge pressure to the Main L.O. Pump discharge pressure upstream of VPR-1--so that's probably why the Trip Oil pressure is building up when the Aux. L.O. Pump is started while the Main L.O. Pump is running.
Either there's a leak in some pipe/tube of the Main L.O. Pump (upstream of VPR-1), or there's a problem with VR-1, or the Main L.O. Pump internal clearances are increasing for some reason, which is causing a drop in flow and pressure (which can't be compensated for with a change in the setting of VR-1).
That's about all I can think of. Use the L.O. System P&ID and the L.O. Tank Internal Piping Arrangement drawing to work through the possible causes. And, again, the problem could be the pump itself, or VR-1. If adjusting VR-1 doesn't increase the pressure then the problem could be with VR-1, OR it could be that the pump is failing and no adjustment of VR-1 can compensate for the loss of pump flow/pressure. The easiest thing to do is to remove VR-1 to check it's operation, and if it's found to be operating properly then either there's a piping leak somewhere or the Main L.O. Pump is failing. And, to get access to the Main L.O. Pump it will likely be necessary to open the Accessory Gear Box.
Please write back to let us know what you find!
Thanks for sharing valuable information.
We will inform to you after replacing the VR-1 during shutdown of machine.
Thanks for the feedback! Please do let us know what you find as you work to solve this problem.
The self regulators VPR 1, 2 are fail open valve as per P&ID.
Suppose if VRP 1 diaphragm punctured, what will be the affect on trip oil and header pressures? my understanding is that it will cause to increase the bearing header pressure?
My understanding is that if VPR 2 diaphragm punctures header pressure will drop as valve outlet is connected to drain lube oil tank.
Can you elaborate please?
I would have to see the relevant P&ID to comment; there have been several different schemes employed over the years--all similar, but slightly different.
Can u share your mail so that i can send to you the diagram.
Or i will provide my mail ID:Chiranjeevi.Sornapudi@hpcl if you can reply to that.
Moderator's Note: why don't you share it on Google Docs or similar platform so everyone can see it?
Normally VPR-1 is a relief valve but a proportional valve. It doesn't have a diaphragm and will fail to close, but BHEL sometimes do some strange things. VPR-2 should be sensing the Bearing Header pressure and can be installed to dump excess pressure to the tank on some machines.
As CSA says, really we would need to see your P&ID to be sure. There should be inspection/adjusted doors or covers for both valves which you should be able to open and see what the valves are doing.