What was found
DURING INITIAL DESCENT FROM FL350 TO FL330, LOWERED CABIN PRESSURIZATION FROM 36 TO 34, AND CABIN ALTITUDE CLIMBED QUICKLY. WITH CABIN PRESSURE WARNING LIGHT, PUT ON OXYGEN MASK AND FOLLOWED CABIN ALT TOO HIGH POH PROCEDURE. DID NOT CORRECT PRESSURIZATION ISSUE. BEGAN EMERGENCY DESCENT AND DECLARED EMERGENCY. DESCENDED TO 7000 FT AND THEN CANCELED EMERGENCY AND LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE PERFORMED AN OPS CHECK OF CABIN PRESSURIZATION SYSTEM IAW MM 21-30-5. OPS CHECKED GOOD. FOUND A DAMAGED TUBE AT VALVE 36H. FABRICATED A NEW TUBE IAW GMM VOL. 1, 8-4-8. INSTALLED SERVICEABLE MANUAL PRESSURIZATION SELECTOR VALVE. TESTED PRESSURIZATION IN MANUAL AND AUTO IAW MM 21-30-50. TESTED GOOD.