Hydraulic ratchet trouble


Our site one of the GE Frame-6B unit is having ratchet trouble.

Earlier when unit was on cool down we used to get "ratchet trouble" but shaft is rotating. In the past two days with the same alarm shat is not rotating.

Hydraulic ratchet pressure is 50 bar and 20CS is getting energized and engaged the shaft (L33CSE = 1). Hence 20 CS ruled out.

One month back line filters FH5 & FH1 were replaced with new one. Hence filter issue ruled out.

Though Hydraulic ratchet pressure is 50 bar, we replaced VR5 and result is same. Hence VR5 ruled out.

When placed on cooldown L33HRF is true so limit switch is working well. Hence 33HR ruled out.

BUT if L33HRF is true, it is not come back to original state L33HRF = 0, so ratchet motor is continuously running without any rotation.

So problem might be in the forward /reverse stroke solenoid ports OR HM2 (cylinder part of forward & reverse stroke).

Please share your ideas /views.

Take care

Bob Johnston

Pretty good analysis Rajesh but it still might be a little short on pressure. You've done all the right things in changing filters, VR, etc. How old is the machine? As ratchet systems get older, the leakage past the ratchet piston seals can increase a bit and the pressure that worked before can become a bit marginal. What is happening is you are not getting a forward stroke so the ratchet will run forever waiting for 33HR to change over. Has their been any recent work done on the drive train? turbine, gearbox, generator? Maybe something is a little "tighter" than it was before and needs a little more torque. Keep is informed but your troubleshooting is good so far.
What kind of sequencing block do you have on this unit? One of our units had an identical problem of continuous ratcheting with no shaft rotation. The ratchet cycle would start on the reverse stroke and as soon as the cylinders started to pressurize on the forward stroke the reverse stroke would start again. The limit switch 33hr is directly connected to the spool piece in the pilot fluid control directional valve. When the cylinder starter to pressurize on the forward stroke there was enough of a pulsation in the oil to operate the spool piece and limit switch. The problem we had was solved by inverting the L33HR-1 input in the MK6. Now the ratchet cycle starts and finished on the forward stroke. We've not seen this problem since. fyi .. our self sequencing blocks are made up of Rexroth 4WH series valves.
For the majority of GE-design heavy duty gas turbines with ratchet mechanisms for cooldown operation (including the self-sequencing ratchet controllers), L33HRF is a logic "1" <b><i>at the </i>END<i> of the forward stroke, and </i>REMAINS<i> a logic "1" until the ratchet reaches the end of the retraction stroke.</b></i>

In other words, it is a logic "1" during the entire retraction stroke.
Thank you for Bob Johnston,309EGuy and CSA for your replies.

We had replaced self sequencing block and problem is same. We haven't do any maintenance in the past 9 months. We had done MI before 2 years but torque converter area not touch. Clutch was de-engaged and manually started ratcheting by pressing jog switch BUT again the problem is same. (we thought without load it may work well)

It manufactured by Rexroth.

So next our doubt is on torque converter.

If anybody having other opinion, please share with us.

Take care
We had replaced hydraulic ratchet pump with new one and pressure is same as earlier 50 bar. So in next outage we are planning to replace torque converter.

Take care
Dear All,

We have solved the ratchet issue. After 2 weeks trial. We end up with valve VM2 which is used for engage-deengage the clutch.

We had replaced torque converter and hydraulic ratchet motor before replace the valve VM2. Earlier we checked VM2 and clutch is engaged and de-engaged well, so it not strike in our mind.

Thanks for all your support.

Take care