ACR LGT MAKES A RAPID DSCNT AFTER LOSING CABIN PRESSURE AND AUTOMATIC DEPLOYMENT OF OXYGEN MASKS IS EXPERIENCED.

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ACFT WAS DISPATCHED WITH AUTOMATIC PRESSURE CTL INOP -- REQUIRING USE OF MANUAL PRESSURE CTL -- A VERY UNUSUAL SITUATION (THIRD OR FOURTH TIME IN MY 14 YRS AS CAPT ON ACFT). DURING CLBOUT THROUGH APPROX 17000 FT CABIN ALT HORN SOUNDED INDICATING CABIN ALT 10000 FT. DEPRESSURIZATION PROCS WERE FOLLOWED; CARGO HEAT OUTFLOW CLOSED AND MANUAL PRESSURE CTL CLOCKWISE TO STOP CABIN CLB. CABIN CONTINUED CLBING AS DSCNT WAS COORDINATED WITH CTR AND INITIATED. PAX OXYGEN MASKS DEPLOYED AS CABIN ALT WENT THROUGH 14000 FT BEFORE ACFT COULD BE DSNDED THROUGH THAT ALT. ACFT CONTINUED DSCNT TO 8000 FT. FUEL WAS DUMPED TO MAX LNDG WT AS ACFT RETURNED TO ORD. APCH AND LNDG WERE UNEVENTFUL. CONTRIBUTING FACTORS WERE 1) THE OPERATING MANUAL PROC WITH RESPECT TO OPERATING IN 'MANUAL MODE ONLY' WERE BASICALLY NON-EXISTENT; 2) VERY NEW FE ON PANEL WITH MINIMAL TRAINING WITH RESPECT TO MANUAL PRESSURE OPERATION. 3) A 'FREAK' COINCIDENCE IN THAT THE CABIN ALT NEEDLE WAS SUPERIMPOSED DIRECTLY BELOW THE CABIN PRESSURE DIFFERENTIAL NEEDLE ON THE 'OUTER DIAL/INNER DIAL' DUAL READING GAUGE AT THE INSTANT THE HORN WENT OFF -- MOMENTARILY DELAYING VERIFICATION OF ACTUAL CABIN ALT AND SUBSEQUENT CREW REACTIONS. SUPPLEMENTAL INFO FROM ACN 215778: SINCE TURNING MANUAL CABIN PRESSURE CTL KNOB FULL CLOCKWISE DID NOT ARREST CABIN CTL; THIS LEADS ME TO BELIEVE THAT OUTFLOW VALVE WAS STUCK IN OPEN POS. IN ADDITION; OPERATING MANUAL DOES NOT PROVIDE INSTRUCTIONS ON OPERATIONAL USE OF MANUAL CABIN CTL NOR IS ANY TRAINING GIVEN ON USE OF MANUAL CABIN PRESSURE CTL OPS.