What was found
CLIMBING TO FL 200, PRESSURIZATION WAS NORMAL. ABOVE FL 220 CABIN ALTITUDE CLIMBED AT AN EXCESSIVE RATE. DURING CRUISE AT FL 290, CABIN ALTITUDE 7300 AND A DELTA P OF 7300 FT. WHEN STARTING DECENT AND REDUCING ENGINE POWER CABIN ALTITUDE CLIMBED AT A RATE OF 1500 FT PER MINUTE. RECEIVED A CABIN ALT CAUTION AND WARNING. CABIN ALTITUDE REACHED 10,300 FT WITH A DELTA P OF 1.7. COMPLIED WITH QRH AND PERFORMED EMERGENCY DECENT. FOUND LOW PRESSURE CABIN AIR SUPPLY CHECK VALVE FORWARD SECTION DOES NOT SEAT AND AFT SECTION STICKS IN FULLY OPEN POSITION.