We have a problem to start a MS5001 unit with a diesel motor and a Mark VI control. The unit starts normally but a approx. 43% of TNH the clutch disengages and the turbine trips. We check the jaw clutch and they seem to be ok. The torque converter pressure is too high (130 psig). There was a 20TU that was eliminated and its place a valve with an orifice plate was installed; this valve was found closed and we think that the pressure must be at approx 40-50 psig. What can be the cause which the clutch disengage so early?

Any comment would be appreciated.

 

Please do realise that the clutch will automatically disengage when the turbine is producing more torque than the starting means. Given your comments on 20TU, I think that you may have a problem with the output from the torque convertor. why did you remove 20TU? this solenoid is controlling torque converter output at different stages of the start up. You also say that you have changed the orifice, this also may be the problem. When did this problem start? Was it after the 20TU modifications?

 

voyager2_kbc,

If you have the typical jaw clutch assembly the teeth are shaped such that as long as the starting means (the diesel engine in your case) is transmitting torque to the turbine shaft through the torque converter the torque will keep the teeth engaged and the jaw clutch closed. As soon as the torque from the starting means/torque converter drops off (when the turbine shaft half of the jaw clutch over-runs the starting means half of the jaw clutch the teeth will disengage and springs will open the jaw clutch and keep it separated so that the teeth will not "chatter" and get physically damaged.

You didn't not when the 20TU was removed, or if the problem started at the time 20TU was removed and replaced or some time after the swap was done. In other words, did this problem start as soon as the solenoid valve was swapped out, or did it work for some time (weeks, months, years .?.?.?) and then this problem just started? The timeline is not clear.

But, what should be clear is that as long as there is sufficient torque being transmitted from the starting means (diesel engine) through the torque converter that the jaw clutch halves will remain engaged (by the design of the teeth) and that as soon as there is insufficient torque from the starting means/torque converter the teeth will disengage and springs will keep the jaw clutch open when the turbine is accelerating and running, and during shutdown.

You didn't say if the diesel seems to be working correctly or not. Is the speed the same as before? Are the diesel air filters clean? Are the diesel fuel filters clean? How long since the diesel was checked out by a qualified diesel mechanic--specifically, when was the last time compression checks were done on the diesel? Has someone recently worked on the diesel and possibly mis-adjusted the linkage (or does the unit have an electronic control module (ECM) controlling the diesel speed)?

The answers to many issues like this can usually easily be troubleshot by asking the question, "When did this problem start?" which means, "What has changed?" Of course the mechanical department never reassembles anything incorrectly, or forgets to put a valve in the correct position, or installs the wrong orifice or forgets to install an orifice.

It's always that darned turbine control system--just look at all of the wires and lights and electronic parts (they're just magic--and evil, too). NOT!!!

So, tell us when the problem started (after a maintenance outage? what was done during the maintenance outage); after the 20TU solenoid was replaced (which is a questionable move to begin with, but I don't want to take the discussion in that direction--it was done, and apparently it won't be undone); some time after the swap? Is there a new diesel fuel supplier for the diesel starting engine? Has the torque converter been worked on recently? (Is it time the torque converter was refurbished--how long since it was last refurbished?) Is the diesel engine working as it should? Has anyone observed the fuel rack to see if it's at a limit or is working as it should?

Please write back to let us know what you find!

 

Excuse me CSA, for being so brief in my explanation. The 20TU was removed many years ago, and in its place was installed an orifice plate with a gate valve. Originally the machine could run with gas and oil. but after the 20TU was removed, the machine runs with gas fuel only, because all the component belonging to fuel oil system were removed. The diesel motor was refurbished last month. In the first attempt to start, the diesel maintained a speed of 2000 rpm (in the previous years it always maintained this speed and the turbine always started up with this speed) but the clutch disengaged at 2200 rpm. At this moment that I am writing to you, I think that I have to measure the diesel speed at the moment when the clutch disengages to evaluate if there is a problem with the control pump (the pump that accelerates the governor). What do you think?. The diesel does not have an ECM.

Regards,
Voyager2_kbc

 

Volyager2_kbc,

I re-read your original post, and you said the valve which was installed in place of 20TU was found in the closed condition. Some of the 20TUs opened to "spoil" the torque converter, and others closed to "pressurize" the torque converter, so without being able to see the Starting Means Piping Schematic it's difficult to say for sure what the correct position should be. It's still a questionable move, but, as I said before--it's probably not going to be undone so it will remain as is and since everything had been working fine for years it's even less likely to be undone. Oh, and, of course, it wasn't the Mechanical Department's fault the valve was not in the correct position--it's certainly the turbine control system's fault, because it's the reason the solenoid was replaced with a manual valve in the first place!

So, more missing information--the diesel was rebuilt. EVERY time I've been on site after the diesel was rebuilt it either failed to break the turbine away from zero speed on START or it wouldn't accelerate the unit or it would shut down when commanded to. Most diesel mechanics don't understand the throttle control linkage and control oil pump and adjustments that are used on these gas turbine starting diesels. It's always best if someone from the plant get to know this part of the system very intimately because it's customary for them to get re-assembled incorrectly.

Some torque converters are 1:1 'transmissions', but most are not. Most have a different output speed than input speed, but, again, we don't know what the torque converter nameplate says. And, we don't know if you're talking about diesel speed or turbine speed. Usual turbine speed for disengagement was about 50-60% TNH, and that usually depended on the health of the diesel and the torque converter.

I don't know if the control oil pump on the diesel is the problem, more likely the adjustment of linkages and stops. I've also seen many diesels fail to stop when the diesel stop solenoid (sorry; I forget the device number--20D-something, maybe 20DS.?.?.?) was energized. They were usually quarter- to half-turn solenoids and when the mechanic put the stop solenoid back on the fuel rack pinion they usually didn't adjust the position of the stop solenoid so that it would turn the pinion far enough to shut off the fuel.

So, even though the diesel gets rebuilt (new cylinders and/or rings and/or pistons and valves and such) many times the mechanics are just completely unfamiliar with the fuel control devices and adjustments and don't get them set correctly after the rebuild. Usually, they can get them set to get the unit started and idling, and accelerating--but unless someone from the plant stands over them and tells them precisely how the linkages and solenoids are to be set they usually don't get set correctly after refurbishment. And, then someone goes and tweaks the control system to put more fuel in to "help" the newly refurbished diesel accelerate the unit because they don't realize the problem is a mis-adjusted diesel speed control mechanism.

Best of luck--and write back to let us know how you fare!

 

Hi voyager2_kbc

Did you manage to solve the issue you were having regarding the clutch disengaging too early? I am having the same issues and wondered if you had resolved your issue.

Any help would be appreciated.

Thanks
Turbinecontrols

 

Hi, Turbinecontrol:

>Did you manage to solve the issue you were having regarding
>the clutch disengaging too early? I am having the same
>issues and wondered if you had resolved your issue.

==============================================

Well, the problem was solved but I was not at site when this occurred. I heard something that made me feel a fool. The motor diesel was refurbished and they installed fuel injectors of a lower capacity of the one the motor diesel had, but nobody told that until we started having problems. I did not follow this problem anymore but I understand that they solved the problem by installing new fuel injectors of the right capacity. I do not think this is your problem but with the explanation that CSA and Glenmorangie have given, I am sure you can solve your problem. Excuse me for writing so late... I do not read these topics with a high frequency

regards,
voyager2_kbc

 

voyager2_kbc,

Thanks very much for the feedback! It's the little things (like under-sized fuel injectors) that can cause big problems. I'll bet the fuel rack was hitting the maximum stop under load, which would have meant either the rack was misadjusted during re-assembly or there was a fuel flow-rate restriction of some sort, but under-sized injectors would not have come to mind after checking many other things.

Anyway, again--thanks for the feedback. We like to say, "Feedback is the most important contribution!"(c) to threads here at control.com, because it's what let's others know if the information provided was helpful or not. In this case it wasn't, but we now know what the problem was (and I'll not forget this in the future!).