What was found
TAKEOFF FROM P/NS 15-20 MINUTES IN FLIGHT, RECEIVED 3B CAUTION MSG. WRH COMPLETED AND 3B WAS TURNED OFF ABOUT 20 MINUTES LATER BEGAN TO RECEIVE INTERMITTANT HYD 3 LO PRESSURE MSGS. THE PRESSURE THEN RETURNED TO NORMAL. THE GEAR WAS PUT DOWN FOR LANDING AND THE PRESSURE DROPPED ALL THE WAY TO 0 PSI. WE HAD TO MANUALLY LOWER GEAR. REPLACED 3A & 3B HYD PUMPS REFERENCE AML PAGES 22949621, 22, 23 & 26 FOR SIGNOFFS AND OPS CHECK. GEAR SWING FOR VERIFICATION PERFORMED IAW CRJ 200 AMM 32-30-00.