What was found
CABIN ALTITUDE WARNING DESCENDING THROUGH FLIGHT LEVEL 220. CABIN ALTITUDE WAS 10,100. EMERGENCY DECLARED TO GET AN EXPEDITED DESCENT TO 10,000 FEET. ***EMERGENCY DECLARED*** CHECKED LEFT PACK CONTROLLER FOR FAULTS, NONE FOUND. PERFORMED LEFT PACK CONTROLLER BITE CHECK, BITE CHECK PASSED. PERFORMED LEFT PACK SYSTEM LEAK CHECK, FOUND DELTA PRESSURE LINE ON LOW LIMIT VALVE OVER FOUR TURNS LOOSE, TIGHTENED SAME. PERFORMED CABIN PRESSURE CONTROLLER BITE CHECKS WITH NO FAULT FOUND. PERFORMED PHASE III PACK FLOW RATE CHECK WITHOUT ISSUE. PRESSURIZED AIRCRAFT WITH BOTH ENGINE PNUEMATICS AND APU, PERFORMED CABIN PRESSURE LEAKAGE CHECK, CHECKED ALL DOORS, HATCHES AND WINDOW SEALS. NO LARGE LEAKS NOTED. CHECKED EQUIPMENT COOLING EXHAUST VALVE FOR DEFECTS, NONE NOTED. REF 757 M/M 21-31-00-5, 21-51-11-2, 21-51-00-5, 21-51-14-5 AND 21-58-05-5. NOTE, AIRCRAFT OPERATING UNDER SINGLE PACK OP'S DUE TO RIGHT PACK DEFERRED.