What was found
TE FLAP DISAGREE DECLARED AN EMERGENCY. SELECTED FLAPS 25@ 170 KTS. DID NOT EXCEED 137KTS ON THE GO AROUND ON THE GO AROUND AND VECTORS BACK TO FINAL. COMPLIED WITH MTSI 27-50/6926, NO FAULTS NOTED. VERIFIED FLAP HANDLE POSITION IS WITHIN LIMITS WITH PDU AND LEFT/RIGHT FLAP POSITION TRANSMITTERS, REF MM27-58-01-5. RAN FLAPS SEVERAL TIMES WITH ELECTRIC PUMPS, NO FAULTS NOTED. PERFORMED ENGINE RUN WITH LEFT ENGINE HYD PUMP SUPPLYING POWER, FLAPS WOULD COME TO A BRIEF STOP BETWEEN 20 DEGREES AND 25 DEGREES. SUGGEST R&R LEFT SYSTEM PRESSURE RELIEF VALVE REF MM 29-11-29-4. THIS VALVE HAS A HISTORY OF CAUSING THIS PROBLEM, REF MX CONTROL. REMOVED AND INSTALLED LEFT SYSTEM RELEIF VALVE IAW AMM 29-11-29-4 . LEAK AND OPS CHECK GOOD. REMOVED AND REPLACED LH EPD IAW AMM 29-05-4-1, LEAK AND OPS CHECK GOOD.