A B737-500 DEVELOPED HIGH 'B' SYS HYD PRESSURE AFTER TKOF AND SUBSEQUENTLY AN ENG DRIVEN PUMP OVERHEATED. THE CREW ELECTED TO RETURN TO THE DEP STATION.

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AFTER A NORMAL PREFLT; TAXI; AND TKOF; I NOTICED THE 'B' HYD SYS PRESSURE FLUCTUATING BTWN 4000 AND 0 PSI AS WE CLBED THROUGH APPROX 1000 FT AGL. ABOUT 10000 FT; THE AMBER MASTER CAUTION LIGHT BEGAN TO FLICKER. THE 'B' HYD PRESSURE WAS NOW STEADY AT 4000+ PSI AND THE HYD BRAKE PRESSURE WAS ABOUT 3800 PSI. WE INITIALLY LEVELED OFF AT 17000 FT TO INVESTIGATE THE PROB; BUT SOON REQUESTED FL200 IN AN ATTEMPT TO CLB ON TOP ABOVE ANY ICING POSSIBILITY. THE NEXT INDICATION WAS THE ILLUMINATION OF THE ELECTRIC 1 'B' SYS HYD PUMP OVERHEAT LIGHT. WE RAN THE 'HYD OVERHEAT LIGHT ON' CHKLIST AND TURNED OFF THE ELECTRIC 'B' PUMP. THE OVERHEAT AND OVERPRESSURE CONDITION CONTINUED. DISPATCH AND MAINT WERE CONTACTED ON COMRDO. MAINT SUGGESTED TURNING OFF THE ENG DRIVEN PUMP AND TURNING ON THE ELECTRIC PUMP TO SEE IF THIS WOULD ALLEVIATE THE OVERHEAT. THE OVERHEAT LIGHT SOON EXTINGUISHED; HOWEVER; THE PRESSURE WAS STILL SOMEWHAT ELEVATED. THE 'B' ELECTRIC PUMP VOLUME OUTPUT IS 1/3 OF THAT OF THE ENG DRIVEN PUMP. BECAUSE OF THIS AND THE FACT THAT SYS PRESSURE WAS STILL SOMEWHAT ELEVATED; I ELECTED TO RETURN INSTEAD OF CONTINUING. DISPATCH CONCURRED WITH THIS DECISION. I DID NOT DECLARE AN EMER SINCE ALL HYD SYS WERE PRESSURIZED AND OPERATING WELL. THE LNDG WAS NORMAL. SUPPLEMENTAL INFO FROM ACN 639037: THE OVERPRESSURE CONDITION CONTINUED. SIMULTANEOUSLY; I CONTACTED COMMERCIAL RADIO FOR A PHONE PATCH WITH DISPATCH AND MAINT. I THEN TOOK OVER COMS AND FLYING DUTIES WHILE THE CAPT WORKED WITH THE COMPANY. THE CAPT AND I AGREED THAT RETURNING TO IAD WOULD BE HIGHLY LIKELY AND I STARTED TO COORD A RETURN TO DULLES WHILE REMAINING WITHIN 60 NM OF THE FIELD. AS A PRECAUTION; THE CAPT AND I DISCUSSED AND REVIEWED THE LOSS OF 'B' SYS IRREGULAR PROC SO WE HAD A BACK-UP PLAN. WE HAD DISPATCH NOTIFY IAD WE WERE RETURNING AND THEY ASKED FOR THE FIRE TRUCKS TO GIVE US THE ONCE OVER AFTER WE LANDED AT IAD AS A PRECAUTION. THE CAPT THEN FLEW A COUPLED APCH ('A' AUTOPLT) TO MINIMUMS AND MADE AN UNEVENTFUL LNDG. THE FIRE CHIEF GAVE US A THUMBS UP ON TXWY Y7 AND WE THEN PROCEEDED BACK TO GATE.