Narrative:

At FL350; we initiated a normal xfeed event. After a few mins; we got into an area of moderate turbulence. Xfeed was complete; I turned the xfeed valve to close and simultaneously instructed my first officer to talk to the flight attendants and passenger about the turbulence and have them all be seated. I subsequently requested lower from ATC for a better ride. Once we started the descent to FL310; we noticed the xfeed valve light was illuminated. We could not tell if it was bright or dim. All main fuel tank pumps were on at this time. We double-checked both fuel quantity gauges and at that time noticed no imbal. We proceeded with the QRH. After reviewing the QRH; 'xfeed valve inoperative' checklist in its entirety; we could not guarantee; with certainty; the actual position of the valve. We communicated extensively with dispatch through ACARS and brought maintenance into the loop as well. We noticed an imbal starting to occur with equal throttle position. Circuit breakers checked in and normal. We attempted differential thrust for a short period of time. This did not correct the imbal. The 'high-side' gauge fuel quantity did not show any movement through the entire event. After conferring with dispatch; we decided to divert to ZZZ. We declared an emergency as a precautionary measure and landed uneventfully. Upon landing we had an imbal of between 2000 and 3000 pounds. Aircraft handled normally in the air and on the ground. Logbook entry was made and aircraft handed over to maintenance. It's hard to say. In hindsight; if we could guarantee the valve was in fact open; I would have crossfed out of the heavy tank. Not knowing the actual position of the valve; I was reluctant to turn off any fuel pumps and cause further problems. The fact that the high side fuel gauge was not moving was also a concern for further complication.

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Original NASA ASRS Text

Title: B737-300 DEVELOPED A FUEL IMBALANCE AFTER CROSSFEEDING. THE IMBALANCE INCREASED AND THE POSITION OF THE CROSSFEED VALVE COULD NOT BE DETERMINED. FLT CREW DECLARED AN EMER AND DIVERTED.

Narrative: AT FL350; WE INITIATED A NORMAL XFEED EVENT. AFTER A FEW MINS; WE GOT INTO AN AREA OF MODERATE TURB. XFEED WAS COMPLETE; I TURNED THE XFEED VALVE TO CLOSE AND SIMULTANEOUSLY INSTRUCTED MY FO TO TALK TO THE FLT ATTENDANTS AND PAX ABOUT THE TURB AND HAVE THEM ALL BE SEATED. I SUBSEQUENTLY REQUESTED LOWER FROM ATC FOR A BETTER RIDE. ONCE WE STARTED THE DSCNT TO FL310; WE NOTICED THE XFEED VALVE LIGHT WAS ILLUMINATED. WE COULD NOT TELL IF IT WAS BRIGHT OR DIM. ALL MAIN FUEL TANK PUMPS WERE ON AT THIS TIME. WE DOUBLE-CHKED BOTH FUEL QUANTITY GAUGES AND AT THAT TIME NOTICED NO IMBAL. WE PROCEEDED WITH THE QRH. AFTER REVIEWING THE QRH; 'XFEED VALVE INOP' CHKLIST IN ITS ENTIRETY; WE COULD NOT GUARANTEE; WITH CERTAINTY; THE ACTUAL POS OF THE VALVE. WE COMMUNICATED EXTENSIVELY WITH DISPATCH THROUGH ACARS AND BROUGHT MAINT INTO THE LOOP AS WELL. WE NOTICED AN IMBAL STARTING TO OCCUR WITH EQUAL THROTTLE POS. CIRCUIT BREAKERS CHKED IN AND NORMAL. WE ATTEMPTED DIFFERENTIAL THRUST FOR A SHORT PERIOD OF TIME. THIS DID NOT CORRECT THE IMBAL. THE 'HIGH-SIDE' GAUGE FUEL QUANTITY DID NOT SHOW ANY MOVEMENT THROUGH THE ENTIRE EVENT. AFTER CONFERRING WITH DISPATCH; WE DECIDED TO DIVERT TO ZZZ. WE DECLARED AN EMER AS A PRECAUTIONARY MEASURE AND LANDED UNEVENTFULLY. UPON LNDG WE HAD AN IMBAL OF BTWN 2000 AND 3000 LBS. ACFT HANDLED NORMALLY IN THE AIR AND ON THE GND. LOGBOOK ENTRY WAS MADE AND ACFT HANDED OVER TO MAINT. IT'S HARD TO SAY. IN HINDSIGHT; IF WE COULD GUARANTEE THE VALVE WAS IN FACT OPEN; I WOULD HAVE CROSSFED OUT OF THE HVY TANK. NOT KNOWING THE ACTUAL POS OF THE VALVE; I WAS RELUCTANT TO TURN OFF ANY FUEL PUMPS AND CAUSE FURTHER PROBS. THE FACT THAT THE HIGH SIDE FUEL GAUGE WAS NOT MOVING WAS ALSO A CONCERN FOR FURTHER COMPLICATION.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.