Ratchet problem


Thread Starter



we had a problem in ratchet, where the sequence is coming continually. due to that we change the both with new one, filter and the 20cs-1 and the sequence valve. but again the same is action were we just now completed our MI. after that we facing lot of problem in ratchet while first start up. we can't able to ratchet it, can't able to rotate the shaft then we change the voith mechanism with new one. after that it able to rotate the shaft. but the sequence is it engage with the shaft and rotate after 45 deg it come fully disengage and comes out after the time again it engage and rotate.

after this went for 1 hrs. after that the ratchet come in a continues one. please let me know the port operations of the sequence valve and the related materials. please send me the link.

<b>Moderator's note</b> Punctuation in the first paragraph of this message is mine. There were no commas or periods.

Venkatachalam, Valliappan X

In my experience, we faced similar problem in one of the turbines where the ratcheting was continuously ON. After executing the "STOP" command once, the problem disappeared.
Experience ratchet pump both AC and DC pump cut-in during ratcheting operation.

Found motor pump rubber coupling was wear & tear and caused deliver discharge pressure low.

I remember 20CS-1 is for clutch engage and disengaged signal.
You haven't told us what Frame size the machine is, or what kind of hydraulic ratchet system you have (self-sequencer, or individual pressure switches on forward- and retraction stroke rams).

I'm going to presume the unit has a self-sequencer mechanism (small block-shaped device with some electrical and tubing connections). The general configuration of this type of ratchet system is that if it doesn't see a change of state in the stroke feedback (a "limit" switch actuated by a plunger in the self-sequencer) then it will continue to attempt ratcheting.

You need to review the Starting Means P&ID to make sure that all the manual valves in the system, specifically for the engagement of the jaw clutch, are fully and completely in the proper position.

There is also usually a manual push-button for "jogging" the ratchet mechanism from the area of the Accessory Gear. If that switch is continually depressed, wired incorrectly, or otherwise not working/configured properly then the hydraulic ratchet logic will continue attempting to ratchet the machine without the normal 3-minute pause between ratchet operations.

I suspect a combination of issues; incorrect valve position(s), incorrect wiring/input configuration, problems with the jaw clutch and/or self-sequencing limit switches, a problem with the manual JOG push-button/wiring, etc.

Again, start with making sure all the manual valves in the hydraulic ratchet/jaw clutch tubing are in the proper places. Check to make sure the pressure output of the hydraulic ratchet pump is correct (see the Device Summary for any expected pressures), and make sure the limit switches on both the self-sequencer and jaw clutch are working properly. Check to make sure the JOG pushbutton is working/wired properly; many sites install a "clamp" to allow the button to remain depressed without a person having to push the button.... and these have been inadvertently left engaged causing the Speedtronic to be wrongly blamed for continuous ratchet operation.

The self-sequencer mechanism only monitors the pressures at the ends of the forward- and retraction strokes, switches the hydraulic flow to the opposite piston when the ends of strokes are reached, and actuates a limit switch (33HR-1) when the forward stroke is complete (and the limit switch remains actuated for the entire duration of the retraction stroke until the retraction stroke is completed), The Speedtronic monitors the limit switch state, and when appropriate energizes the necessary solenoids and pump motor, and then de-energizes them until the next stroke is to be completed. I believe some self-sequencers also have a small solenoid-operated valve (energized and de-energized by the Speedtronic), but it's been a long time since I've worked on a self-sequencer and I don't have access to a Starting Means P&ID, and not the P&ID for the turbine at your site.

Please, in the future, provide more information about the system at your site. There are multiple types of hydraulic ratchet systems, though these days the most common one is the "self-sequencer" type of system for most Frame 5s and Frame 6Bs. Frame 7Es & 7EAs with ratchet systems don't use a self-sequencer mechanism like the 5s/6Bs do, though operation is similar just with more inputs to the Speedtronic. Also tell us about how the starting means is coupled to the shaft (jaw clutch; SSS clutch; hard coupling; etc.). The more information about the configuration of the unit at your site you can provide in the original post the better the reply you will likely receive.

We had faced similar problem in one of our frame 5 machine after MI of the machine. But what we found was, for rotating the shaft there is a provision available in the field where we can connect a unit containing switches/buttons to rotate the shaft (this done by mechanical people during their job on the shaft for checking clearances). After completion of the checking this unit has to be removed, else these problem will appear. Check it, this could help you.

We had this type of issue many times. Please look the below thread for more details


One more thing you can verify that, cylinders which used for engaging and De-engaging the shaft. This cylinders are hydraulically engaged and return by spring force. If seal is passing it may not engage properly and ratchet sequence may run continuously, since reverse stroke not happened and switch (33HRF)remain in the same position. So the brief checklist are,

1. VM2 valve
2. Hydraulic cylinders (2 nos)

Take care