Hydraulic Ratchet problem


Thread Starter



I have a problem in hydraulic ratchet (gas turbine frame 5 mark VI),

The problem appears after shutdown or trip. when the shaft reaches zero speed after that the ratchet takes 1 or 2 sequence after that the sequence is not correct when the pump 88HR and 20CS energized again after 10-12 sec the 33hrf energized become {1} and still energized with no shaft rotation and high electric current in 88HR motor and hydraulic ratchet trouble alarm appears. its still energized until I open the breaker of 88HR.

The problem appear after trip or shutdown and gone almost after 2 hours of the problem and after that the ratchet rotate the shaft and the sequence is ok but hydraulic ratchet trouble alarm appear for 3 sec and then become normal.

Appreciate your cooperation with me
Hi Ayman,

We had a similar problem and rectified after replaced the four way manual valve (VM-2) which is used to de-engage the shaft.

If the valve is passing, the system won't get enough hydraulic pressure to make rotation.

Since you said 20CS is energized, there won't be any issue there. But confirm it's coil resistance.

Inspect inlet filters for contamination.

Take care

Thanks for the feedback, but what you're reporting is kind of, well, odd.

Running a turbine compartment ventilation fan during cooldown generally causes the axial compressor casing to cool--and "shrink"--more quickly that the compressor rotor. This usually causes rubs, which cause the tips of the compressor blades to touch the compressor casing, which usually causes the rotor to bind and not rotate.

Many Frame 5s had a common accessory/turbine compartment vent fan, which drew air in to the Accessory Compartment, under the inlet, and discharged the air into the turbine compartment. While it was desirable to cool the Access. Compt., it is not desirable to cool the Turbine Compartment for the reason above. Even if there is no common vent fan, if you are running a fan to cool the Turbine Compartment you are increasing the chances of causing a compressor casing rub, which will usually result in a failure of the ratchet to be able to turn the shaft for many hours.

If you are running the Access. Compt. vent fan to cool the Access. Compartment and that is allowing the ratchet mechanism to operate correctly, that would seem somewhat odd, as well. If the ratchet had been working correctly previously, something would have had to have changed to require cooling to allow the ratchet to work properly.

Now, all of this being said, I am presuming there is no sequencing/logic that ties operation of the vent fan to cooldown--other than to shut down the turbine compartment vent fan during ratchet operation.

So, I'm very confused about the feedback.... It doesn't make a lot of sense--to me, anyway.

Can you provide some clarity? What vent fan is being run or shut off? Was some vent fan being manually run before that was causing the ratchet not to work properly?

Please. I'm very confused. Help me understand.
Dear all,

The sequence of cooldown is:
cooldown time: 10 hours
ventilation fan running during cooldown: 2 hours

in this first two hours the problem is happened.
we faced this problem in the previous power plant (8x25MW) GE solved that by sequencing the ventilation fan running during cooldown to be:

running 3 min
stopped 20 min
and the problem is solved.

In our new plant we make the same thing but manually by starting the vent. fan for 3-4 min and then stopped it manually for 16-20 min and the ratchet work properly so we asked GE to find solution by changing the logic as detailed.

The ventilation fan is to cool both the accessory & Turbine compartment

Thank you all
I am wondering if the vicker valve has a coil about to fail in it. Cooling a bad/failing coil can sometimes allow it to work for a bit longer.

When you say there is a high current draw by the hydraulic pump dc motor, I have seen that very thing when the vicker valve fails and doesn't port the oil to the rod end of the ratcheting hydraulic cylinder.

A failed vicker valve can cause the 120 dc pump motor to fail if the circuit is left energized too long with nowhere for the pressurized oil to go.

The vicker valve has a small hole in the coil end of it that allows you to check for movement when the circuit is energized. If you check for movement and there is none when the compartment is hot yet there is after the fan has been ran, then the coil is failing.

Mark Allen
I've been working on GE-design heavy duty gas turbines for nigh on 30 years, and although I've seen valves manufactured by Vickers used on some GE turbines, I've never heard a valve in the ratchet mechanism called a "vicker valve". And we try pretty hard here on control.com to use the same terms and device numbers GE uses for devices.

MarkAllen, can you please tell us the device number of the vicker valve, or where to find it on the ratchet mechanism? I've ass-u-me-d (yes--I've gone and done it again) the unit has a hydraulic ratchet self-sequencer (VH14-1, or VH-14--same thing). Is the vicker valve part of the hydraulic ratchet self-sequencer?

I've considered this possibility as well, but--and I didn't ask this question because, yet, again, I ass-u-me-d something here--there was no mention of the shaft not turning during these events. Also, since the same fan cools both the turbine and accessory compartments and because running the fan will cause the compressor casing (and turbine shell) to cool faster than the rotor, I did ask Ayman for clarification about when the fan was running. I have, under instructions from engineering, stopped turbine/accessory compartment vent fans from automatically running at all during Cooldown (via a sequencing modification) because running the fans during Cooldown caused rubs and the shaft to stop turning during ratcheting.

So, again, I would ask both Ayman and MarkAllen for clarifications. I know that Frame 5s are now being engineered and built by the former Nuovo Pignone (now known as GE Oil & Gas), but I would have thought they would have experienced compressor rubs when the turbine/accessory compartment vent fan is run during Cooldown and would have, similarly, discontinued that practice. (Some vent fans were left running during shutdown and after reaching zero speed and start-up of Cooldown (ratchet) until a temperature switch in the Turbine Compartment shut it down. But, it was found, in the 1980s, that it was causing compressor rubs and so the practice was discontinued then. If GE only know what GE knew....)

I would venture a guess that the fan might be left running for a "brief" period to purge the compartments of any combustible gases, or even cycled for short periods of time for this purpose. But, to run the fan continuously (again, we don't have all the specifics from Ayman) for two hours during Cooldown greatly heightens the risk of rubs and "Failure to Ratchet" alarms. And usually, when there's a rub like this (the compressor cooling--and shrinking--faster than the compressor rotor) it takes many hours for the shaft to cool enough to be able to begin ratcheting again.

Here's hoping for some clarifications!
CSA the vicker valve is 20HR.

Also if you will re-read the post where the fellow was first describing the problem you will see where he says the unit ratchets ok the first couple of times then 88HR draws a high current and the turbine shaft no longer rotates.

Mark Allen
Thank, you, MarkAllen, for clarifying which valve you were referring to.

Oh, THAT vicker valve. Actually, I've never seen a Vickers Hydraulics valve used for that application--but I haven't seen every ratchet implementation, either.

Would you also call 20CS-1 a "vicker valve"? Are you referring to any hydraulic solenoid valve as a "vicker valve"?

I was never really clear about the first post, nor any of Ayman's other posts to be honest.

If the Turb/Access Compt. vent fan continues to run after a trip/shutdown as is typical, then it's difficult to understand why 20HR isn't being "cooled." The thing here is that it wouldn't be exposed to oil temperature until the ratchet pump operates, and I believe the ratchet pump draws directly from the L.O. Tank and not from the cooled L.O. Bearing Header, but I don't have a Starting Means Piping Schematic to refer to as I write this, so I may be wrong about that. If the ratchet pump is taking a suction directly from the uncooled oil in the L.O. tank, that might be part of the problem but it's not clear.

Again, just when this vent fan runs and how it is or isn't associated with the ratchet sequencing (which is kind of the implication from Ayman). But, again, nothing is very clear to me about this post. While I'm grateful for the feedback, it poses more questions that it answers.

And, I'm beginning to wonder if we're going to get any clarification(s) from Ayman.
Hello CSA

I am not sure what 20CS-1 is, the Schematic I have for these units (1970 vintage GE Frame 5) does not show a device 20CS-1.
There is a 20CS which does happen to be a Vicker valve as well but it is used to engage the coupling.

20 HR is a hydraulic solenoid valve used to port the oil to either the base-end or the rod- end of the hydraulic ratchet cylinder 30HR, depending on the position of the Snap-Switch (Sorry no device name is given on the schematic I have).

Yes you are correct that the Hydraulic Ratchet pump 88HR takes suction directly from the lube oil sump.

From Ayman’s description of the problem it seemed to me that after just a few ratcheting sequences the hydraulic pump was becoming locked hydraulically and causing the high current draw of the 125 vdc pump motor.
He goes on to state that for a few moments “hydraulic ratchet trouble alarm appears for 3 sec and then become normal.”

On the units I work on, more often than not when that happens either the Snap-Switch isn’t making up the circuit to the Vicker-Valve 20HR or the circuit is being made up and there is 125 vdc present at 20HR and the coil in 20HR is open of shorted.

I thought that possibly the coil in 20HR had only partially fail and the cooling effect of the vent fan might have cooled the coil enough to allow it to begin functioning again.

Mark Allen

The problem is gone after we turn on the ventilation fan for (3-5 min) and turn it off for (20 min). we still make that for the first hour of cooldown, and then we let it running without stop it for the second hour of cooldown, and then it will stopped due to the sequence of ventilation fan running during cooldown (2 hours)


20CS-1 and 20CS are the same. Usually, most times even if there was only a single device many engineers would include a -1; sometimes, they wouldn't.

I had a feeling you were working with an older machine. Does that machine have a Hydraulic Ratchet Self-sequencer (VH14 or VH14-1)?
Hi All,

I'm new here. I handling a turbine type MS6001B. I having an alarm - Ratchet motor overload.

When during normal ratcheting, no alarm appear. it does smoothly for a few hrs. But suddenly an alarm appear showing TCQA P125-N125 overvoltage. It show alarm/ normal for some times then ratchet motor overload alarm appear. Causing the motor trip. only when i reset the motor, the ratchet run as normal. Try to remove both FH1 & FH5 filters and inspect. Found no blockage. Reinstall & run ratcheting again. alarm starts to appear again after a few turn.

Could any of you, guys help me out.

Hello, Carlos,

So, the Diagnostic Alarm you cited could come from any of three TCQA cards in a TMR panel (or only one in a SIMPLEX panel). But, we would need to know which TCQA(s) annunciated the alarm--<R>, <S>, or <T>.

The Diag. Alarm basically says that there is some kind of "spike" in the 125 VDC supply to the Mark V. Usually it requires a spike of approximately 140 VDC to cause this alarm, which is dangerously close to the voltage level that can cause the TCPS cards to shut themselves down and/or blow fuses.

Most Frame 6Bs use a DC motor for hydraulic ratchet pump motors. These DC motors have brushes and commutators, and brushes and commutators require replacement and maintenance. It is conceivable that failed brushes or commutator problems are causing arcing which is causing voltage spikes which are causing the Diagnostic Alarm. Usually, when brushes begin to fail or fail, excessive current is also a symptom--which is what is causing the TOL (Thermal OverLoad) relay to annunciate the 'Ratchet Motor Overload' alarm. (I don't recall if the TOL actuation usually trips the Ratchet Pump Motor or not; but if you say it does at your site, then it does at your site.)

When any motor overload alarm is annunciated, the first thing to do is to use an ammeter (clamp-on or in-line series) to measure current being drawn by the motor and compare it to the motor nameplate value to see if an overload condition actually exists (overload of the motor means more current than rated will be drawn by the motor).

Also, it's a good idea to check the "heater" strip in the TOL relay to make sure it's not damaged, and to compare the part number to a catalog to determine if the strip's range is applicable to the motor being used. Finally, there is usually a manual knob on the TOL relay to adjust the TOL sensitivity from approximately 90% to 110% of the strip rating. I've seen completely incorrect TOL strips installed in TOLs; I've seen TOLs severely damaged by extreme current flow (usually it's also found that the TOL contacts have been jumpered to prevent "nuisance" alarms in this case); I've seen damaged TOL relays that require replacement.

But, it's still a good idea to, first, check the brushes and commutator of the DC ratchet pump motor. If the brushes are worn and need replacement and haven't cause damage to the commutator then possibly just replacing the brushes with a new set will solve the problem. Depending on the age of the machine and how long it ratchets between runs it might just be a good idea to replace the brushes and inspect the commutator anyway.

Then, be sure the TOL is working correctly, has the proper strip installed, and the manual adjustment knob is in the proper position. (For example, the TOL strip might have a rating of 3.65A, but the motor nameplate current is rated for 3.41A. In this case, the TOL manual adjustment knob should be set to something less than 100%, approximately (3.41/3.65=93%). 100% is usually when the pointer on the knob is at the horizontal position; turning the knob to make the pointer point down from horizontal would be setting the TOL below 100%, while turning the pointer up from horizontal would be setting the TOL above 100%.)

Finally, I have seen hydraulic ratchet pump problems cause a ratchet motor overload, and even hydraulic ratchet piston problems cause a ratchet motor overload.

But, based on the information provided, my money's on worn DC motor brushes and/or a worn DC motor commutator. But, while you're checking it's best to methodically check all possibilities so you can eliminate what is not causing the problem as you prove what is causing the problem.

Please write back to let us know what you find.

[P.S. When comparing the TOL strip part number (for a GE TOL strip) to a catalog or part list, you will likely need to add CR120B to the numbers on the strip. So, if the strip has '278C' stamped on it, the entire part number would be 'CR120B278C', and that would be the number you would look for on-line or in a GE TOL catalog to determine the ampere rating for the strip.]

Thanks for the feedback.
Now monitoring the current, before arrange the motor for repair.

Will update once done.