A B737-500 CREW RPTS THAT A FAILING ENG BLEED AIR VALVE CAUSED THE CABIN ALT PRESSURE WARNING HORN TO SOUND. EMER NOT DECLARED. THE FLT CONTINUED AT FL230.

Narrative

WHILE PERFORMING THE AFTER TKOF CHKLIST; THE CAPT (PNF) NOTICED LOW BLEED READINGS FOR THE R ENG BLEED. BOTH PACKS APPEARED TO BE OPERATING CORRECTLY AND THE CABIN APPEARED TO BE CLBING AT A NORMAL RATE WITH BOTH THE CABIN ALT AND THE CABIN DIFFERENTIAL INCREASING. WE GOT A LEVELOFF AT FL230 SO I (THE CAPT) CHKED THE BLEED READING AGAIN. THE NEEDLE INDICATION WAS STILL LOW; ABOUT 12 PSI. I PLACED A SELCAL INTO DISPATCH AND MAINT. WE WERE ASSIGNED A HIGHER ALT AND AS EVERYTHING; WITH THE EXCEPTION OF THE NEEDLE READING; SEEMED TO BE OPERATING NORMALLY; THE CLB WAS INITIATED. WHILE CLBING; MAINT AND DISPATCH CAME ONLINE AND SOME TROUBLESHOOTING BEGAN. WHILE THE TROUBLESHOOTING WAS IN PROGRESS; THE ADDITIONAL PROC FOR BLEED VALVE INOP WAS COMPLETED. AT THIS TIME I NOTICED THE CABIN WAS CONTINUING TO CLB AND WAS AT 9000 FT. I REQUESTED A DSCNT BACK TO FL230. WHILE WAITING FOR A CLRNC FOR THE DSCNT; THE CABIN ALT HORN WENT OFF. THE FO AND I BOTH PUT ON OUR MASKS AND ESTABLISHED COMS. CLRNC FOR THE DSCNT WAS GIVEN AND INITIATED. WE EXPEDITED OUR DSCNT AND LEVELED OFF AT FL230. THE CABIN DSNDED WITH US AND SHOWED ZERO CLB AT THAT ALT. MAINT DETERMINED THAT THE #2 ENG BLEED VALVE WAS THE CAUSE. WE REMAINED AT FL230 AND PROCEEDED TO ZZZ SINGLE PACK. WE DID NOT DECLARE AN EMER AS ATC RESPONDED QUICKLY TO OUR REQUESTS. THE MASKS DID NOT DROP; AND THE PAX THANKED US FOR A NICE FLT.