Narrative:

While performing the after takeoff checklist; the captain (PNF) noticed low bleed readings for the right engine bleed. Both packs appeared to be operating correctly and the cabin appeared to be climbing at a normal rate with both the cabin altitude and the cabin differential increasing. We got a leveloff at FL230 so I (the captain) checked the bleed reading again. The needle indication was still low; about 12 psi. I placed a SELCAL into dispatch and maintenance. We were assigned a higher altitude and as everything; with the exception of the needle reading; seemed to be operating normally; the climb was initiated. While climbing; maintenance and dispatch came online and some troubleshooting began. While the troubleshooting was in progress; the additional procedure for bleed valve inoperative was completed. At this time I noticed the cabin was continuing to climb and was at 9000 ft. I requested a descent back to FL230. While waiting for a clearance for the descent; the cabin altitude horn went off. The first officer and I both put on our masks and established communications. Clearance for the descent was given and initiated. We expedited our descent and leveled off at FL230. The cabin descended with us and showed zero climb at that altitude. Maintenance determined that the #2 engine bleed valve was the cause. We remained at FL230 and proceeded to ZZZ single pack. We did not declare an emergency as ATC responded quickly to our requests. The masks did not drop; and the passenger thanked us for a nice flight.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of January 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.