I would like to ask you about a problem we had recament at a GE MS5002C turbine, and I hope you can give me an answer.

the problem is summarized as follows:
When starting the hydraulic pump 88HQ was high alarmed DP hydraulic oil filters 63HF and high vibration at the auxiliary compartment. we changed the cartridges without result. the cartridge was downright extracted and let the empty filter again the same thing. we installed new manometers upstream and downstream of the filters without result. the pressure upstream and downstream 90 bar to 80 bar was dismantled. the three-way valve was found no plugging.

is new oil.
temperature 42 ° C

<b>Moderator's Note:</b> I fixed some spelling and punctuation. Couldn't figure out what "recament" was.

 

Have you tried adjusting VR22, the relief valve for the Aux. Hydraulic pump? Are you sure the problem is not coming from the Main Hyd. pump? Just guessing but the vibration from the Aux. compartment is suspicious.

Try to Crank the machine and shut down the Aux. Hydraulic pump. if the pressure is high, adjust the pressure regulator on the Main Pump (usually VPR3). also check the Main Pump Relief valve VR21 is set to spec.

Please report back and we can follow up.

 

We just finished the MI revision. The turbine is not yet started, and not coupled to the load (compressor).

First of must do the HP and LP overspeed test.
all that has been done yet. The box was filled with new oil. we heated the oil with resistances and 88QA T = 42 ° C. so far everything is good.

But when it starts the HQ, the problem arises at high pressure differential filters hydraulic oil 63HF confirmed by gauges installed upstream and downstream of the filters DP = 10bar. the pressure upstream 90 bars and downstream 80 bars and high vibrations into auxilliary compartment.

We replaced the cartridges. We checked the three-way valve. We even did the test with the empty filter (without cartridge).

The problem remains: 88HQ on = high DP hydraulic oil filters with vibration at the auxiliary compartment.

thank you so much, and have a great day
greetings

 

With the turbine shut down, have you tried running the 88HQ (88QA should also be running)? With the door to the accessory compartment open, and someone near by looking at the 88HQ pump to see what is shaking? Maybe the pump is not properly installed (loose bolts, maybe).

 

There is something a bit strange here, the 88HQ discharge pressure should only be around 75 Bar. are you sure VPR22 is not dumping because of over pressure? have you looked at VPR22 dump? I think that may be the noise in the Accy. Compt. If your system is not coupled to your compressor yet, do you have anything plugged on the Hydraulic System discharge for testing at the moment? that would cause high pressure because of low flow. It really shouldn't be possible to get 90 Bar from 88HQ. Can you post a copy of your Hydraulic system P&ID or email to me at [email protected].

 

As Bob Johnston says, if the discharge pressure of the Aux. Hyd. Pump is higher than normal then the differential across the hydraulic filters will also be higher than normal.

Another possibility is that the wrong hydraulic filters have been installed which are causing a very high differential. If filters were purchased from another supplier and weren't properly chosen for the application this could cause a high differential by restricting the flow. (This is common when sites try to purchase a filter with a smaller particle rating to try to prevent servo valve problems.)

Sometimes, during major inspections piping is disassembled which also dislodges dirt which collects in low points and elbows.

Another possibility is that replacing the lube oil charge may have caused dirt in the lube oil reservoir to be dislodged and that's contributing to the high differential. A lot of times, when lube oil is replaced it's suggested to perform a flush of both the lube oil system AND the hydraulic systems. To flush the hydraulic system it's necessary to remove the servo valves and install flushing blocks in their place. The hydraulic pressure will be very low during flushing because of the high flow and the inability of the pressure compensator on the hydraulic pump to increase the flow to maintain pressure--but flushing will occur.

Lastly, it's very common for sites to use the relief valves to set hydraulic pressure instead of the built-in pressure compensator on the hydraulic pump(s). The only way to test/set the relief valves is to increase the pump discharge pressure using the pressure compensator until the relief valve opens and note the pressure. When the relief valve cracking pressure has been set/verified it's then necessary to use the pump pressure compensator to reduce the pressure to the system rating (per the Device Summary value). If the pump pressure compensator is set higher than the relief valve this can usually also be seen by an increase in the current drawn by the Aux. Hyd. Pump motor.

The hydraulic system is basically a static system--meaning that there's very little flow under steady-state operating conditions. Only when the fuel valves or the IGVs or the second-stage nozzles are moving is there any substantial hydraulic flow. (For a hydraulic actuator to remain in a stable position there must be NO flow to or from the actuator.) There is usually a small weep of flow through some servo-valves but it's very small. Also, there is usually a small flow through the air-bleed check valves on the hydraulic manifold, but it's also very, very small.

Please write back to let us know what you find!

 

Good answer CSA but

1) They did say that they had tried the system without filters and still had the same problem??

2) Do remember the Aux. Hyd. pump usually doesn't have a pressure regulator, it just runs flat out.

I reckon you are right CSA, I think there is a blockage in the system somewhere!

 

Bob Johnston,

It's been a long time since I've worked on a Frame 5 (unfortunately), but if I remember correctly most GE-design heavy duty gas turbines use the same hydraulic pump for both the Main and the Auxiliary. The difference is that the main is mounted horizontally on the Acc. Gear Box, and the Aux. is mounted vertically underneath the Aux. Hyd. Pump Motor. I'm pretty certain, because I've swapped pumps from the Aux. to the Main (when the Main failed--not my choice; the Customer's), and whenever I've had to adjust Aux. Hyd. Pump pressure I've cussed the location and nearly dropped the cover more than once into the L.O. Reservoir until I learned to tie a string and tape it to the nut before removing it.

Maybe some of the BAs/MAs/licensed packagers of GE-design heavy duty gas turbines did something different; I haven't worked on that many of them over the years and I do know that a lot of the auxiliaries were similar--but not exactly the same.

If there is no pressure compensator on the Aux. Pump, how does the pressure get set? By the relief valve? Hmmm....

Anyway, thanks for the info!