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Starting Jaw Clutch Disengaging and Engaging During Ratcheting
After the shut down of our MS5001GE gas turbine, the ratcheting sequence has not be operating properly in the sense that the clutch disengages and engages.

HI,

I am an upcoming engineer and i would like to know why our MS5001 GE gas turbine is disengaging and engaging during a ratchet operation. we shut down the unit, and after it has coasted down to 0%, the 88HR came up and the 20cs was energized to engage the jaw clutch and ratcheting began but the clutch did not fully engage. after few seconds, the clutch started disengaging and would engage almost immediately then the jaw turns in the reverse direction before traveling back to engage the other half of the clutch and then turns a little before the end of the forward stroke.

what could be the problem?
thanks

1 out of 1 members thought this post was helpful...

Hi,

Does the hydraulic ratchet system use a self-sequencing mechanism, usually called VA14-1, I believe)? (Upcoming engineers should always consult the P&IDs for the equipment they are working on/responsible for; the best upcoming engineers have their own set of P&IDs that they can write on and highlight as they see fit as they study and refer to them over time. P&IDs have the device numbers for the various components on them.)

If so, have you checked all the filters in the hydraulic ratchet system? Usually there are no differential pressure gauges or -switches across the filters of the hydraulic ratchet system; it's a good idea to install do gauges at the earliest possible time when next replacing the filters.

Have you checked the speed of the Hydraulic Ratchet pump motor?

What when 20CS-1 is energized, some of the discharge from the Hydraulic Ratchet pump is used the close the jaw clutch with two small hydraulic cylinders against the spring pressure which is trying to keep the jaw clutch halves disengaged. The design of the jaw clutch teeth should help keep the jaw clutch engaged during a forward ratchet stroke (when the shaft is being turned). When the shaft is at zero speed, I believe 20CS--1 is always energized during ratchet operation--both forward- and reverse strokes. And at the end of the the reverse (retraction) stroke (as indicated by the change of 33HR-1) the self-sequencer goes back into a forward stroke and the turbine control system starts a timer (usually three seconds); this is done to help keep the jaw clutch engaged when the Hydraulic Ratchet system is off for the next three minutes.

From your description, it does not seem like the hydraulic cylinders used to engage the jaw clutch are fully engaging the jaw clutch halves. One reason may be misalignment of the two jaw clutch halves. Another reason may be that 20CS-1 is not working properly or is plugged with dirt.

From the information provided, it seems that for whatever reason the jaw clutch halves are engaging and remaining engaged during ratchet operation. So, either something is preventing the hydraulic cylinders from closing the jaw clutch, or 20CS-1 is not allowing enough oil to get to the hydraulic cylinders to allow the cylinders to close the jaw clutch.

Please write back to let us know what you find and how you resolve the problem!

1 out of 1 members thought this post was helpful...

Thanks a lot for the prompt response.

Surprisingly, the L33HRF which we tried to reset several times since the issue started without any positive result. was again reset this morning and the clutch became fully engaged then ratchet sequence was normalized.

Your explanation of the whole process will definitely aid my understanding of both the P&ID and manual.

Thanks once again

1 out of 1 members thought this post was helpful...

Thanks for the feedback.

>Surprisingly, the L33HRF which we tried to reset several
>times since the issue started without any positive result.
>was again reset this morning and the clutch became fully
>engaged then ratchet sequence was normalized.

L33HRF is a logic signal that goes to a logic "1" at the end (completion) of a forward stroke. it remains a logic for the duration of the retraction (reverse) stroke, and changes to a logic "0" at the completion of the retraction (reverse) stroke. It remains a logic "0" through the entire forward stroke and when it finishes the forward stroke it changes to a logic "1" again; and so on.

For units with a self-sequencer, 33HR-1 is a limit switch which is activated by a plunger which moves at the end of the forward stroke and moves back at the end of the retraction stroke. It's not uncommon for the plunger to get gummed up with oil and dirt and stick in one position or the other, or not fully extend or not full retract.

And since it is a mechanical mechanism it does wear out over time, requiring replacement of the self/sequencer assembly. Also, the internal seals of the self-sequencer can eventually wear out.

If I recall correctly, the oil supply to the hydraulic ratchet pump and devices is unfiltered oil from the L.O. Tank, which is another reason why filters should be changed frequently, and why do gauges should be installed across all filters and checked at least once per shift when the unit is on Cooldown (hydraulic ratchet).

Again, thanks for the feedback!

Hope this helps!

By Chiranjeevi on 26 July, 2017 - 11:06 am

CSA,

Can you explain how the pressure from this self sequence valve will help in getting forward and reverse strokes? is there any separate power cylinders for this forward and reverse stroked? i am an control engineer. i don't know exactly how it works exactly.

Our machine is frame 5 machine.

2 out of 2 members thought this post was helpful...

Chiranjeevi,

Every control engineer worth his salt needs to know how to read and understand P&IDs--no matter how hard or difficult that might seem. GE P&IDs are among the easiest in the world to understand--and I know that because I read and study a LOT of P&IDs, not just GE P&IDs. To be able to understand the controls of any process one needs to know, first, what the process is supposed to do and when, and, second, how the systems and components work together to do that. Most of the field devices (on the turbine and auxiliaries in this case) connected to the control system are shown on the P&IDs. And those which aren't, are shown on electrical schematics (which is another "form" of a P&ID).

If the unit was indeed packaged and provided by GE, the Operations & Service Manuals provided with the unit WILL have the P&IDs (GE calls them Schematic Piping Diagrams, or "Piping Schematic") for the unit, and there will also be a tab in the Manual for each of the systems for which there is a P&ID. In each tab in the Manual for the systems, there will be a brief description of the system, its components, and how they are supposed to work together to achieve the desired operation.

In general (except on very old Frame 5s), the hydraulic ratchet mechanism is a part of the torque converter, and can be found on the 'Starting Means' P&ID. There are two cylinders/pistons for the forward stroke (because it requires more torque than retraction) and one cylinder/piston for the retraction stroke. The self-sequencer detects when the cylinder piston(s) has(have) reached the end of its travel (because the pressure will go very high when the piston can't move any further), and redirects the output of the ratchet pump to the other cylinder, and so on.

Always use the unit-specific Manuals to find information about the unit at your site. They are good places to start--the BEST place to start, actually. And, when you need specific help, we are here at control.com to provide that help.

Lastly, if you find anything you read to be of help, click on the 'Thumbs Up' at the right of the post or response. If you need clarification, or if you don't find the information useful--PLEASE, write for clarification or tell us why you don't find the information useful. That's the only way we can improve our posts/responses--if we know why it wasn't useful.

Hope this helps!

Thank you for the information. Meanwhile, I am with my P&ID for MS6001B GE, The Operating manual has not been given to me. Can you please explain how the forward stroke and the reverse stroke is achieved as I could not understand their direction?

Thanks

1 out of 1 members thought this post was helpful...

The ratchet control module has what I guess you could call a mechanical flip-flop valve which is controlled by the forward and reverse stroke piston oil. In forward stroke, the ratchet has a mechanical device which grabs the shaft and rotates it, in reverse stroke the mechanism free wheels (like a bicycle) and returns ready to produce another forward stroke.

There is a limit switch (33HR) installed which detects forward and reverse stroke of the module and reports back to the control system

Hope this helps.

1 out of 1 members thought this post was helpful...

Rotimi88,

We don't know and presume the hydraulic ratchet mechanism you are referring to is a late-model system, with a self-sequencer (VH14-1 (I mis-typed in an earlier response above) that controls the flow of hydraulic oil (L.O.) to the forward pistons and the retraction piston, which are usually contained in the torque converter mechanism.

A forward stroke is a pushing movement by (usually two) cylinders to rotate the turbine shaft approximately 45 degrees in the counter-clockwise direction (the normal direction of rotation). Once the end of the forward stroke has been reached, a limit switch, 33HR-1, changes state to indicate to the end of the forward stroke and remains in this state all during the retraction stroke. The "flip-flop" valve in the self-sequencer changes the flow of hydraulic fluid from the forward cylinder(s) to the retraction cylinder.

A retraction stroke is, as glenmorangie said, a (usually single) cylinder that "resets" the engagement mechanism by rotating the engagement mechanism in the opposite direction of the forward stroke cylinders. The shaft doesn't turn during a retraction stroke. When the end of the retraction stroke is reached, 33HR-1 changes state again and remains in this state until the end of the forward stroke is reached. And so on.

The whole sequence is started very simply by starting the hydraulic ratchet pump and supplying pressure to the self-sequencer. And, the self-sequencer, for the most part, takes care of the rest. The turbine control monitors the state of 33HR-1 (L33HRF, or l33hrf), primarily to know when the retraction stroke is complete. The programming in the turbine control system senses the end of a retraction stroke (when L33HRF changes state to a logic "0", usually) and then starts a short timer. When the self-sequencer completes the retraction stroke, the "flip-flop" valve ports hydraulic oil to the forward stroke cylinder(s) to begin another forward stroke--but the timer in the turbine control system shuts down the hydraulic ratchet pump and waits, usually approximately 3 minutes, before re-starting the hydraulic ratchet pump. The purpose of the short forward stroke is to help keep the jaw clutch teeth engaged between forward strokes. And, it also "pre-positions" the hydraulic ratchet system to start on a forward stroke on the next cycle.

It's a pretty simple system that relies on several things to work properly. Clean oil supply to the self-sequencer is critical. Usually, the hydraulic ratchet pump draws unfiltered oil from the L.O. reservoir, so the filters on the supply line to the self-sequencer should be changed regularly! (And rarely ever are. There is no differential pressure gauge installed across the filter, and no visual indicator to tell when the filter gets dirty. And, because it's usually never changed, the filter element eventually ruptures and then all kinds of dirt gets into the self-sequencer. The hint here is: Install a differential pressure gauge across the filter--and monitor it during ratchet operation, and change the filter regularly, if it needs it or not!).

Also, the adjustment of the jaw clutch mechanism is very important. The teeth must engage properly for the mechanism to work properly, and to stay engaged between ratchet cycles when the unit is on cooldown. And, there is a limit switch on the jaw clutch mechanism which must also be adjusted properly for the ratchet--and starting system--to work properly. There are springs on the jaw clutch mechanism which must be in good condition, and there are hydraulic cylinders on the mechanism which must be in good working order. (Some newer turbines use a SSS (Shifting, Self-Synchronizing) clutch mechanism, which doesn't require springs and cylinders, but it does still require a switch (in this case a proximity switch).

Please work with your supervisors to obtain access to the Operations & Service Manuals. And, once you have access to them, take the time to page through them, page by page (yes--this takes time). BUT, you will be absolutely astounded by the information that is contained in them. The System Descriptions for each of the P&IDs can be brief, but can be instrumental in understanding and deciphering the P&IDs and the system components and intents. There should be a document somewhere in the Manuals called 'Piping Symbols Drawing' which is a nearly all-inclusive document of all the symbols used in the P&IDs (kind of a "cheat-sheet" for the symbols)--which is almost as important as the P&IDs themselves. And, again, there is (or should be) a System Description for each of the P&IDs.

I recommend making the largest size copy you can make of the P&IDs--one for yourself, and one for the Operators in the Control Room. This is so that you can make notes on the P&IDs, showing the opening/closing temperatures or pressures of temperature switches and pressure switches and the calibration scaling of pressure transmitters, etc. You find this information, mostly, on the 'Device Summary' which is another crucial document to have a personal copy of.

Hope this helps!

Take a look at your P&ID. There is a forward power stroke and a reverse freewheel stroke from the Ratchet Sequencing Module. Take a look at your manuals. There should be a description there on how the ratchet operates.