GE Gas turbine Frame VI Ratchet Trouble


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We have using 2 nos 2*30MW GE make Gas turbine Frame VI which faces frequent ratchet trouble during shut down or cooldwn ON process and though 88HR running pressure does not built upto 60-70 Kg/cm2. While we press the plunger of 20CS (ratchet SOV) for initial time the pressure built up to 60-70 Kg/cm2 and ratcheting proceeds. We have checked 20CS,33HRF,33CSE,88HR ok.

Is there is problem in "Self Sequencing Block," i.e,.any jam in the two cylinders of "Self Sequencing Block"?

Please suggest and share information regarding this.

When you press the plunger of 20CS, it seems to work okay. That says 20CS isn't working, but you say you've checked it. Working would be defined as providing the necessary force to operate the plunger. Presuming there's not something sticking in the self-sequencer.

Dirty oil is usually the culprit. There should be a filter upstream of the self-sequencing. Unfortunately, there's not usually a differential pressure gauge across the filter (hint!) so they have been known to rupture and release all of the dirt trapped inside into the self-sequencer.

I don't have a starting means piping schematic for a ratchet with a self-sequencer, so I can't remember exactly what 20CS does... I seem to recall 20CS was to engage the jaw clutch (I'm presuming the unit has a jaw clutch). It's been so long, I can't recall; sorry.

But, it sounds like you're on the right track.

I would add to CSA, if I can. L20CS is true when the jaw clutch is closed. As I recall the jaw clutch is applied via hydraluic pressure from the hydraulic ratchet pump via 20CS-1 the starting clutch solenoid. If hydraulic pressure is low then the clutch may not be able to apply. Usually once the unit shuts down the clutch will apply once the unit reaches zero speed, and the way the jaw clutch locks together it will not disengage until the unit overruns the torque converter.

If I understand you are somehow "helping" the clutch apply by forcing the hydraulic cylinders that push the jaw clutch together? Then once the clutch indicates engaged the ratchet sequence operates normally? It sounds like something is wrong with the clutch apply solenoid, 20CS-1, or the cylinders that actuate the jaw clutch, or lastly that the hydraulic pressure is lower than required for some reason. If you can provide more information as to what state some of these signals are in it might help narrow the possibilities.

Hopefully it may just be a simple problem of low hydraulic pressure from 88HR.
Certainly sounds like a problem with the 20CS solenoid, do remember guys that 20CS normally ports oil to the hydraulically operated porting valve at the the inlet to the sequencing module. You didn't mention, but I would replace FH5 and FH1 which are the inline filters before and after PH3(88HR) and also check out the inline relief valve VR5 before the sequencing module. All of these will give lower pressure than normal. If you have a VM2 hand valve fitted which will isolate the clutch from the ratchet sequence, open it and try sequencing the module without the clutch engaged, this will check the sequencing of VH14 and let you be sure that the sequencing module is sequencing correctly. Good Luck and report back
Seems to be a problem with 20 CS, when you are pressing the plunger you are ultimately forcing L20CS1X. Only after L20CS1X, L4HR will go live. With this sequence the ratchet will operate and the feed back will be available through L33CSE. I think you need to recheck the 20 CS. Without the schematic, it is difficult to directly suggest anything else
what is VH14? i know it is sequencing module but what is its task?
is it an electronics or it is mechanical part?
It's a good idea when you have a new question, even though it's related to an existing thread, to start a new thread so as to avoid confusion.

VH14 was designed and built before electronics were around that could withstand the high temperatures and vibration which exist in the Accessory Compartment where the 'Hydraulic Ratchet Self-Sequencer' is mounted.

You should be able to see a diagram of the device on the Starting Means Piping Schematic (P&ID) drawing. It usually is just a small series of internal passages that monitors pressure levels and switches the direction of hydraulic pressure between the forward- and retraction stroke ports of the ratchet mechanism.

It usually has a single "micro-switch" (not user-replaceable) to indicate when the unit has reached the end of the forward stroke and is directing hydraulic pressure to the retraction port of the ratchet mechanism. The switch's contacts are usually driving a contact input signal named L33HRF, which translates into "The forward ratchet stroke has been completed and the system is in retraction" when the signal is a logic "1".

There is usually a System Description for each system which has a Piping Schematic drawing in the instruction manuals provided with the unit. There is usually a very basic, and generic, description of important system components in the System Description.

There should be some filters in the Hydraulic Ratchet system. Filter require maintenance, and these are no different from any other filter in this regard. Most of the Hydraulic Ratchet system filters I have seen on turbines do not have a differential pressure indicator of any kind, so it's just a good idea to replace them on a periodic basis (like once per year; they're not expensive when one considers the alternative, which usually involves a lot of frustration, down-time (lost production), and troubleshooting).

When filters get really dirty, what usually happens is that they rupture, which allows a LOT of dirt and crud that was captured in the filter to go downstream. Dirt and crud in small passages in hydraulic control devices and instruments usually lead to erratic operation.
Dear sir

thank you for your elaboration

i need to know if PART NO. P/N: GM499061P003

is belong to this module. otherwise pls clarify this part no. with name and application
dear csa

i could not understand your meaning, please give me more

please send me one picture of vh14 module also if there is any data sheet.
my mail is
chomoos [at]
I would like you to verify the followings.

Go in for a "jogging" operation. If the turning gear, turns continuously as lon as you hold the Jogging push switch, then the 33cs and 20 CS operates OK and the 88Hr and Hyd.Pr. is also OK. Then for "sequencing" check the logics of L2HR-L33HRF-L33HRX-L33HRZ-L33CSE-L20CSX- and monitor the correct sequencing of logic changes in the screen. During sequencing The Shaft must move 180 deg,once in 3 mts on completion of one fwd and one reverse stroke.

Hope this info.will benefit you..

I'm a little confused about your statement that the shaft must move 180 degrees. In my experience, the shaft rotates approximately 1/8 turn (approximately 45 degrees) for each forward stroke/retraction stroke sequence, whether by JOG push button or in automatic operation.

180 degrees of rotation is very unusual. Can you tell us more about the ratchet mechanism at your site that turns the shaft 1/2 turn each stroke sequence? What is the manufacturer's name? Who was the packager of the turbine at your site?
Dear CSA and ALL,

I would like to apologise and correct my statement on my previous post, regarding the movement of Ratchet during ratchet cycling. Dear CSA.. You are very much correct to mention that the turning gear moves 1/8 turn which is about 45 deg once in 3 mts during 1 cycle of operation. Pls try to enter the logics mentioned and note the logic changes as per the sequencing. Sorry once again for the grave mistake of mentioning 180 deg.ratchet operation.
(by mistake}.


You replied to a post that was one year old, and to which the originator never responded to any of the questions asked and never indicated the problem had been resolved or not.

And, you also have an "open" post ( in which you have not responded to any of the questions asked of you nor have you indicated if the problem has been resolved or not.

Since you seem to be reading past posts on, you have likely noticed that the most useful posts are the ones where the originator posted feedback to indicate whether or not the information supplied was useful or not. Without feedback, it's difficult to know if the information was useful or not, for those supplying the information, and for those reading the posts later.

We like to say here at that "Feedback is our most important contribution!" (c) because it helps everyone to know what works and what doesn't and what's useful and what isn't.

Also, when originators are asked to provide answers to questions it's always helpful if the answers to all the questions are provided, not just those that are believed to be relevant. If we are asking questions it's because the information wasn't provided in the original post or because we believe the information to be necessary to understand the problem or what's been done to troubleshoot and resolve the problem.

We welcome all information, but I would suggest that when providing information to past posts that you look closely at both the age of the post and the information provided (or not provided, as the case may be) by the originator.

And I would ask that you reply to all the questions in your open post or thank those who have provided information when you post the resolution or indicate the problem has been resolved.