Hydraulic Ratchet Problem

O

Thread Starter

osama111

Hello,

sorry my language is not free well so i will try to explain our problem. The hydraulic ratchet spin 3\4 cycle per 30 min. some times 1.5 cycle (Variable speeds). our engineer decided to change the Torque converter. there is the same problem in the new one. still give Variable speeds within 30 min. finally our turbine frame 7ea.
 
Many newer Frame 7EA units use a hydraulic ratchet mechanism that rotates the shaft approximately 1/8th of a turn every 3 minutes when working properly. They employ a couple of limit switches to sense when the ratchet mechanism reaches the end of stroke (forward stroke; retraction stroke). And, many used Aux. Hydraulic Pump pressure a the source of hydraulic pressure.

If your turbine's configuration is similar to the above description, have you verified that hydraulic pump discharge pressure is normal? Is there a high hydraulic filter differential pressure? Are the hydraulic accumulators properly charged?

What Process Alarms are being annunciated when the the ratchet isn't working properly?

Many Frame 7EAs were provided with a turning mechanism which could be temporarily installed on the turbine-end generator coupling and used to turn the shaft. Are you sure the shaft is moving freely?

What kind of generator is the turbine driving? Air-cooled or hydrogen-cooled? If the generator is air-cooled, is it a GE generator or a Brush generator? If it's a Brush generator, is the lift (jacking) oil system working properly, delivering the proper pressure?

The sequencing for the hydraulic ratchets most commonly used on newer Frame 7EAs is done in the Speedtronic panel, using the above-mentioned pressure switches and a couple of solenoids (if I remember correctly) for switching the hydraulic flow to the forward- and retraction stroke cylinders. Is everything working correctly--the pressure switches and the solenoid(s)?

Without being able to see the Piping Schematics (P&IDs) for the Starting Means- and L.O. Systems it's difficult to say much more than that. Either there's not sufficient hydraulic pressure or hydraulic flow, or there's some problem with the switches and solenoids. If the hydraulic ratchet is part of the torque converter (and most were) and the converter was replaced, but the switches and solenoids weren't--then it could be the switches and/or the solenoids. And, if the generator is air-cooled, they require a lot of torque to turn the shaft, and, in fact, many of the Brush generators which were supplied with some Frame 7EAs even required separate lift (jacking) oil pumps to supply additional pressure to the generator bearings to be able to break the turbine shaft away from zero speed during starting and also during ratcheting. Lift oil was also necessary during shutdown to protect the bearings from damage at very low speed during coastdown.

That's about I can suggest without being able to see the P&IDs/sequencing and without knowing the alarms which are being annunciated when the problem is occurring.

Finally, there were quite a lot of Frame 7EAs which used the torque converters to provide torque during shutdown to keep the shaft turning at 30-50 RPM for cooldown. This was generally referred to as "slow-roll" but I've heard some people (mistakenly) refer to it as "ratcheting." From some of the terms it sounds like you may have slowroll, but, it's not clear.

Please write back to let us know how you fare.
 
Hello,

If I understood correctly, the shaft turns sometimes 3/4 of a full turn, sometimes 1.5 full turns. Did you check if this variation depends on the temperature of the lube oil?

Also, is there any difference if you run one of the lift oil pumps or the other?
 
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