STEERING GEAR CONSIST OF TWO PUMPING UNIT. MOST OF THE TIME ONLY ONE PUMP IS RUNNING WHILE THE OTHER IS STOPPED. IN THIS CASE, THE OTHER PUMP MIGHT GET DRIVEN IN REVERSE DIRECTION BY FLUID UNDER PRESSURE FROM THE RUNNING PUMP. TO PREVENT THIS, THERE ARE TWO METHODS USED:-
1.NON-REVERSING LOCKING GEAR :- THIS CONSIST OF NUMBER OF STEEL PAWLS MOUNTED ON THE MOTOR-PUMP COUPLING AND WHEN THE PUMP ON WHICH IT IS THERE IS STARTED, THESE PAWLS FLY OUTWARD DUE TO CENTRIFUGAL FORCE AND REMAIN CLEAR OF THE STATIONARY STEEL RATCHET SECURED TO THE MOTOR SUPPORTING STRUCTURE. BUT IF THE PUMP STOP, THE PAWLS RETURN TO THEIR NORMAL INWARD POSITION AND ENGAGE THE RATCHET TEETH AND PROVIDE POSITIVE LOCK AGAINST REVERSE ROTATION.
2. AUTOMATIC ISOLATING VALVE :- IS PROVIDED IN BOTH THE PUMP UNITS. THESE VALVES ARE ACTUATED BY PUMP PRESSURE. THESE VALVES HAVE 2 POSITIONS, ONE FOR ISOLATING AND OTHER TO LET GO THE OIL TO THE SYSTEM. THE TWO ENDS OF THE VALVE ARE CONNECTED TO THE TWO PUMPS. ONE END HAS GREATER AREA THAN THE OTHER. NOW THE OIL PRESSURE OF BOTH THE PUMPS ARE SAME. NOW LET PUMP#1 IS RUNNING WHILE THE OTHER IS STOPPED. THE OIL PRESSURE FROM PUMP#1 WILL ACT ON THE END WITH LESSER AREA OF ISOLATING VALVE OF PUMP#2. WHILE THE END WITH LARGER AREA IS CONNECTED TO PUMP#2. SINCE PUMP#2 IS NOT RUNNING HENCE ISOLATING VALVE IS CLOSED AND NO OIL WILL ENTER THE PUMP #2 TO ROTATE IT IN REVERSE DIRECTION. NOW IF PUMP #2 GETS STARTED IT WILL ACT ON LARGER AREA AND SINCE ITS AREA IS GREATER HENCE FORCE ON THIS END WILL BE MORE THAN THE OTHER LEADING TO OIL LET GO TO THE SYSTEM I.E ISOLATING VALVE GETS OPEN. THE END CONNECTED TO PUMP#1 HAS A SMALL HOLE WHICH DRAINS THE REMAINING OIL ONCE THE PUMP#1 STOP SUPPLYING OIL TO THE VALVE AS BYPASS VALVE GETS CLOSED.
