Narrative:

After takeoff from ZZZ runway 32L, #1 'B' hydraulic low pressure light flickered on and off several times. While getting the checklist out, light went out. Approximately 1 min later, both 'B' system low pressure lights came on and system 'B' pressure indicated zero. We performed the loss of 'B' system checklist, then talked to dispatch and maintenance. Maintenance did not have a solution. We talked with dispatch and agreed to return to ZZZ, did a cabin advisory with the flight attendants, and informed the passenger. Flight attendants used excellent CRM and called with a concern about a vibration from the wing. We attributed this to the outboard flight spoiler floating with loss of 'B' system. We advised ATC of our intentions to return to ZZZ. ATC told us that we would have to hold unless we were an emergency aircraft. We declared the emergency with ATC and advised dispatch. We later requested the equipment standing by with ZZZ ATC. Made a normal flaps 15 degree landing in ZZZ on runway 32L. Of interest is the fact that the standby hydraulic pump would not test during the preflight. I found the standby hydraulic circuit breaker out. We reset with ZZZ and standby worked normally. On climb out per earlier fsar, both 'B' system low pressure lights illuminated with loss of 'B' system pressure. Upon arrival in ZZZ, maintenance found 'B' hydraulic pump connections loose. Overnight maintenance performed a 'B' system check per ZZZ maintenance.

Related reports:

Google
 

Original NASA ASRS Text

Title: A B737-300 IN CLB AT 8000 FT DECLARED AN EMER AND DIVERTED DUE TO LOSS OF 'B' HYD SYS PRESSURE AND QUANTITY CAUSED BY LOOSE 'B' PUMP CONNECTIONS.

Narrative: AFTER TKOF FROM ZZZ RWY 32L, #1 'B' HYD LOW PRESSURE LIGHT FLICKERED ON AND OFF SEVERAL TIMES. WHILE GETTING THE CHKLIST OUT, LIGHT WENT OUT. APPROX 1 MIN LATER, BOTH 'B' SYS LOW PRESSURE LIGHTS CAME ON AND SYS 'B' PRESSURE INDICATED ZERO. WE PERFORMED THE LOSS OF 'B' SYS CHKLIST, THEN TALKED TO DISPATCH AND MAINT. MAINT DID NOT HAVE A SOLUTION. WE TALKED WITH DISPATCH AND AGREED TO RETURN TO ZZZ, DID A CABIN ADVISORY WITH THE FLT ATTENDANTS, AND INFORMED THE PAX. FLT ATTENDANTS USED EXCELLENT CRM AND CALLED WITH A CONCERN ABOUT A VIBRATION FROM THE WING. WE ATTRIBUTED THIS TO THE OUTBOARD FLT SPOILER FLOATING WITH LOSS OF 'B' SYS. WE ADVISED ATC OF OUR INTENTIONS TO RETURN TO ZZZ. ATC TOLD US THAT WE WOULD HAVE TO HOLD UNLESS WE WERE AN EMER ACFT. WE DECLARED THE EMER WITH ATC AND ADVISED DISPATCH. WE LATER REQUESTED THE EQUIP STANDING BY WITH ZZZ ATC. MADE A NORMAL FLAPS 15 DEG LNDG IN ZZZ ON RWY 32L. OF INTEREST IS THE FACT THAT THE STANDBY HYD PUMP WOULD NOT TEST DURING THE PREFLT. I FOUND THE STANDBY HYD CIRCUIT BREAKER OUT. WE RESET WITH ZZZ AND STANDBY WORKED NORMALLY. ON CLBOUT PER EARLIER FSAR, BOTH 'B' SYS LOW PRESSURE LIGHTS ILLUMINATED WITH LOSS OF 'B' SYS PRESSURE. UPON ARR IN ZZZ, MAINT FOUND 'B' HYD PUMP CONNECTIONS LOOSE. OVERNIGHT MAINT PERFORMED A 'B' SYS CHK PER ZZZ MAINT.

Data retrieved from NASA's ASRS site as of July 2007 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.