ACR MLG MADE AN EMERGENCY DESCENT WHEN FLT CREW WAS UNABLE TO CONTROL CABIN PRESSURIZATION.

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FLT ATL-TUL-DFW EXPERIENCED PRESSURIZATION PROBS WHILE ENRTE TO TUL. WE WERE IN LEVEL FLT AT FL310 WHEN THE CABIN PRESSURIZATION HORN WENT OFF. THE CABIN ALT WAS AT 10000' AND CLBING. THE F/O SWITCHED TO STANDBY TO TRY AND CTL THE CABIN. WHEN WE REALIZED WE COULDN'T CTL THE CABIN; I TOLD THE F/O TO DECLARE AN EMER AND GET ME 10000'. I DIDN'T UNDERSTAND WHAT ALT THE CTLR SAID AND STARTED TO ASK THE F/O WHEN HE PUT 15000' IN THE ALT WINDOW. I THEN STARTED MY EMER DSCNT. I THEN ASKED HIM TO TRY AND GET ME 10000'. ABOUT 20 SECS PASSED AND 10000' WAS PUT IN THE ALT WINDOW. I RETURNED TO ATL AND MADE A NORMAL LNDG. AFTER WE GOT ON THE GND MY F/O SAID THAT WE WERE ONLY CLRED TO FL240. HE SPUN THE ALT DOWN TO GET ME STARTED. I AM NOT SURE HOW CLOSE TO FL240 I WAS BEFORE I WAS CLRED TO 10000'. NOTHING WAS SAID ABOUT ANY ALT; SO I AM ASSUMING THAT I WAS STILL ABOVE FL240 WHEN I RECEIVED CLRNC TO 10000'. THE F/O WAS TRYING TO RUN THE DSCNT CHKLIST AND DIDN'T REALIZE HE HAD PUT 15000' INSTEAD FL240. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: A BURNED OUT CTL MOTOR ON THE OUTFLOW VALVE CAUSED THE FLT CREW TO LOSE CTL OF CABIN PRESSURIZATION. THE O2 MASKS DID NOT COME OUT AND THERE WERE NO INJURIES TO PAX AS A RESULT OF THE EMER DSCNT.