2 MECHS INSTALLED A CHK VALVE BACKWARDS.

Narrative

ON A ROUTINE SVC CHK OF AN MLG; MECH FOUND A HYD LEAK IN R WHEEL WELL. IDENTING THE LEAK WAS DIFFICULT IN THAT A LINE HAD A PIN HOLE WHICH CREATED A CLOUD OF MIST IN THE WHEEL WELL; MAKING IT EXTREMELY HARD TO SEE AND BREATHE. PRIOR TO IDENTING THE PIN HOLE; THE MECH REMOVED A CHK VALVE ON THE LNDG GEAR CTL VALVE TO REPLACE THE O-RING; WHICH APPEARED TO BE LEAKING (WET). HE REINSTALLED THE CHK VALVE AND LEAK CHKED THE AREA; WHICH CONTINUED TO CREATE A MIST. HE PROCEEDED TO REMOVE A HYD LINE TO ISOLATE THE LEAK; REPLACED THE RIGID LINE WITH AN INTERIM FLEXIBLE LINE AND IT LEAK CHKED GOOD. THE MECH RETURNED THE ACFT TO SVC. AFTER THE ACFT DEPARTED; THE CREW ADVISED OPS CTR VIA RADIO THAT THE GEAR (ALL 3) FAILED TO RETRACT FULLY. THE ACFT RETURNED AND LANDED WITHOUT INCIDENT. TROUBLE-SHOOTING THE LNDG GEAR SYS REVEALED THAT THE CHK VALVE PREVIOUSLY REMOVED HAD BEEN RE- INSTALLED BACKWARDS; LIMITING ALL 3 GEAR FROM FULLY RETRACTING. THE CHK VALVE WAS CORRECTED AND THE ACFT GEAR WORKED PROPERLY. SUPPLEMENTAL INFO FROM ACN 253335: THE CHK VALVE IN QUESTION IS IDENTICAL TO A NORMAL FITTING AND IS NOT CLRLY MARKED. DUE TO CONDITIONS IT WOULD BE VERY EASY TO INSTALL THIS VALVE BACKWARDS IF NOT AWARE OF IT BEING A CHK VALVE.