What was found
WHILE IN CRUISE, HYDRAULIC QUANTITY ON SYSTEM 3 WENT FROM 18% WHEN NOTICED TO 0%. LATER LOST ALL HYD 3 PRESSURE. ELEC PUMPS A AND B WERE TURNED OFF WHEN DIRECTED BY THE QRH. (FLIGHT 6401) FOUND OUTLET PRESSURE UNION ON HYD NR 3 FLOW LIMITER VALVE LEAKING. REMOVED AND REPLACED BOTH HYD NR 3 FLOW LIMITER VALVES PRESSURE AND OUTPUT UNION O-RINGS WITH SERVICEABLE UNITS. SERVICED AND OPERATED HYD. #3 SYSTEM FOR SEVERAL MINUTES. ALL INDICATIONS NORMAL AND NO LEAKS NOTED. AFTER OPERATING WE INSPECTED HYD#3 FILTER DPI'S. NO DEFECTS NOTED. ACFT OK FOR SERVICE. REF AMM. 29-12-19