AN MD80 LOW FLOW LIGHT ILLUMINATED AT FL320. AN EMER DSCNT WAS COMPLETED BECAUSE THE CABIN COULD NOT BE CONTROLLED. THE PAX O2 MASKS DID NOT DEPLOY.

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AT CRUISE ALT OF FL320 THE COPLT NOTICED THAT THE FLOW LIGHT HAD ILLUMINATED. AS THE COPLT WAS INITIATING THE FLOW LIGHT CHKLIST; I NOTICED THAT THE CABIN CLB INDICATOR WAS PEGGED AT ABOVE 1500/FPM CLB RATE; AND CABIN ALT WAS CLBING. WE RECEIVED CLRNC TO DSND BUT HAD NO INOP LIGHTS ILLUMINATED ON THE PRESSURIZATION PANEL. THE R AND L PNEUMATIC SUPPLY PRESSURE APPEARED TO BE NORMAL. AS I CONTINUED OUR DSCNT; THE COPLT STARTED TO INITIATE THE AUTO PRESSURIZATION INOP/MANUAL PRESSURIZATION CHKLIST. THE COPLT SELECTED AUTO #2 AT APPROX FL310 AND THE CABIN RATE OF CLB DECREASED WITH A MOMENTARY BUMP AND THE FLOW LIGHT EXTINGUISHED; BUT THEN THE CABIN CLB RATE QUICKLY INCREASED AGAIN TO GREATER THAN 1500/FPM. AS WE CONTINUED OUR DSCNT IT BECAME APPARENT THAT THE CABIN ALT WAS OUT OF CTL AT WHICH TIME THE COPLT INITIATED THE RAPID DECOMPRESSIONS/CABIN ALT WARNING CHKLIST AS I INITIATED AN EMER DSCNT. WE DONNED OUR OXYGEN MASKS AND AT 10000 FT CABIN ALT THE RED CABIN ALT LIGHT ILLUMINATED AND THE WARNING HORN/VOCAL SOUNDED. THE CABIN ALT APPEARED TO GO ABOVE 14000 FT MOMENTARILY BUT THE PAX OXYGEN MASKS DID NOT DEPLOY AND SINCE THE CABIN ALT WAS RAPIDLY DSNDING WITH THE ACFT'S ALT TOWARD 9000 FT I ELECTED NOT TO MANUALLY DEPLOY THE PAX OXYGEN MASKS. DURING ALL THIS I WAS COORDINATING WITH THE FLT ATTENDANTS WHO STATED THAT NONE OF THE PAX SEEMED TO NOTICE THE DSCNT NOR DID ANYONE COMPLAIN ABOUT THE PRESSURIZATION. THE ONLY APPARENTLY NOTICEABLE EVENT WAS THAT THE REAR GALLEY DOOR WAS MAKING A SLIGHTLY LOUD NOISE DURING DSCNT. ALL OF THE DSCNTS WERE COORD WITH ATC WHO WAS ABLE TO KEEP OUR CLRNCS BELOW OUR DESIRED ALT UNTIL WE REACHED 11000 FT WHERE A MOMENTARY DELAY WAS ENCOUNTERED. AT THIS TIME I DECLARED AN EMER AND RECEIVED AN IMMEDIATE CLRNC TO 9000 FT. AT NO TIME WAS IT NECESSARY TO VIOLATE ANY ATC CLRNCS. THE COPLT WAS STARTING TO MAKE SOME PROGRESS WITH THE MANUAL CTL OF THE PRESSURIZATION BUT HE STATED THAT IT WAS DIFFICULT TO MOVE THE CABIN CTL WHEEL AND WAS UNABLE TO GET THE POS INDICATOR BEYOND THE FLAPS 28 DEG SETTING. AT THIS TIME WE WERE INITIATING OUR LEVELOFF AND I ASKED THE COPLT TO DISCONTINUE HIS ATTEMPTS TO REGAIN CTL OF THE CABIN MANUALLY. AFTER LNDG; I MADE A PA NOTIFYING THE PAX THAT OUR ACFT HAD ENCOUNTERED SOME PRESSURIZATION DIFFICULTIES AND APOLOGIZED FOR ANY DISCOMFORT. NO PAX SAID ANYTHING TO ME CONCERNING THE PRESSURIZATION EXCEPT FOR ONE LADY NEAR THE VERY REAR OF THE AIRPLANE WHO SAID SHE WAS HAVING SOME DIFFICULTY CLRING HER R EAR.