GE frame 7AE main hydraulic oil pump failure SOLVED

Morning,
Thought I might share the results of an investigation we recently had into the failure of our main hydraulic oil supply pump/pressure coming up from an outage.
Long story short, operations noticed that the auxiliary hydraulic oil pump auto-started shortly after the unit reached FSNL for the first time after being down for a routine outage.
The auxiliary pump was manually shut off for a few seconds (held the spring loaded HOA switch off briefly) and we verified that the main HP was unable to maintain adequate hydraulic oil pressure, ruling out a transient pressure blip on start-up (air in the line etc.)
Trouble shooting continued, the unit was brought down. We verified the coupling (plastic) that drives the main hydraulic oil pump and this was in good condition.
The MHP was pulled, and we found black rubber debris in the pump inlet, the pump was replaced and we restarted the unit.
Once we achieved FSNL we encountered the same problem again, taking the unit down a second time we removed and inspected the hydraulic oil supply manifold and found more of this same black rubber debris plugging it up.
With the manifold replaced the unit was successfully restarted and has been running well.
The source of this debris is thought to be from a degredated urethane valve seat in the main lube oil tank switching valve- this valve was actuated 2x during the initial unit outage which is uncommon for us, the lube oil filters are usually able to make it between outages and we've never had to swap them online.

*This also seems to agree with GE TIL 1564 which was originally released in 2007 and then revised in
2009. GE has identified the transfer valve shoe material degradation as a risk to the 7EA fleet.
The transfer valve assembly/housing has to be welded into the LO system piping during construction. If
the transfer valve internals including the shoes are not removed during the welding process, they can be
exposed to excessive heat which can damage the shoe’s urethane material. This material may then later
be released from the transfer valve shoe and enter the LO system*

Cheers.
 
Nice job with the diagnosis and thanks for the feedback. We have 2 units commissioned in 2005 with ~110K fired hours. We replaced the shifting shoes within a couple of years and they looked awful. Hard to believe yours lasted this long. Glad you got it handled, hopefully helps someone else in the future if there are more of those shoes running around!
 
Top