A B737-400 HAD THE R CTR TANK PUMP REPLACED IMPROPERLY RESULTING IN A FUEL LEAK.

Narrative

ACFT XYZ CAME IN FOR A 'C' CHK WITH THE R CTR TANK BOOST PUMP ON MEL AS DYSFUNCTIONAL. A NEW PUMP WAS ISSUED ALONG WITH A SEAL KIT. AFTER REMOVING DEFECTIVE PUMP AND PLACING IT ALONGSIDE ITS REPLACEMENT; IT WAS NOTED THAT THE DELIVERY PORT STEM OF THE PUMP PROVIDED 2 GROOVES FOR O-RING ACCOMMODATION; WHEREAS THE RETURN PORT 1. THE MAINT MANUAL ONLY INSTRUCTS TO REPLACE O-RINGS BEFORE INSTALLATION. SINCE THE O-RING KIT PROVIDED 1 REPLACEMENT SEAL OF MATCHING DIAMETER AND CROSS SECTION TO THOSE SEALS ON THE DEFECTIVE PUMP; THE ASSUMPTION WAS THAT THE SEALS ON THE REMOVED PUMP WERE CORRECTLY PLACED AND THEREFORE TO INSTALL THE SEALS ON THE REPLACEMENT PUMP IN A WAY IDENTICAL TO THE WAY FOUND. AFTER LUBING THE SEALS AND INSTALLING THE PUMP; IT WAS FUNCTIONALLY CHKED BY LISTENING TO THE PUMP MOTOR RUN WHEN THE BOOST PUMP SWITCH WAS PLACED TO THE 'ON' POS MOMENTARILY AT THE FLT STATION. AS THERE WAS ONLY 210 LBS OF FUEL IN THE CTR TANK; NO LEAK CHK WAS ESTABLISHED AT THIS TIME AND NO NOTATION MADE IN THE LOGBOOK TO THIS EFFECT; ONLY ITS OP. AT THE GATE; FUEL WAS PUT INTO THE CTR TANK AND THE PUMP WAS FOUND TO BE LEAKING BY MAINT PERSONNEL DURING WALKAROUND. THE PUMP WAS REMOVED AND WITH THE NEW O-RING SEAL PROVIDED; THE SEAL POS WAS CHANGED ON THE DELIVERY PORT FROM ONE GROOVE POS TO THE OTHER. THE PUMP WAS INSTALLED AND FUNCTIONED WITHOUT LEAKAGE AFTER WHICH THE ACFT DEPARTED ZZZ.