PISTON 2774133 - Caterpillar

Illustration 4 g03665884
Negative flow control operation (bucket control valve in the BUCKET CLOSE position)
(1) Center bypass passage
(2) Return line
(3) Center bypass passage
(4) Passage
(5) relief valve (negative flow control)
(6) relief valve (negative flow control)
(7) Negative flow control orifice
(8) Port
(9) Negative flow control orifice
(10) Passage
(11) Return passage
(12) Negative flow control line
(13) Negative flow control line
(14) Idler pump
(15) Drive pump
(16) Pilot pump
Illustration 5 g01210689
Bucket control valve (BUCKET CLOSE position)
(3) Center bypass passage Illustration 5 shows the negative flow control operation at the main control valve when only the bucket control valve is in the BUCKET CLOSE position.All of the control valves in the left body of the main control valve are in the NEUTRAL position. Center bypass passage (1) is open. All of the oil delivery from the idler pump flows through center bypass passage (1) to negative flow control orifice (7). Since all of the oil delivery from idler pump (14) is restricted by negative flow control orifice (7), negative flow control pressure (PN) in center bypass passage (1) is at maximum pressure. The negative flow control pressure flows through negative flow control line (12) to the idler pump regulator. The negative flow control operation of the idler pump regulator causes the swashplate of the idler pump to move to the minimum angle position. The output flow of the idler pump is decreased due to the increased negative flow control pressure that is created in center bypass passage (1).The joystick for the bucket has been moved fully to the BUCKET CLOSE position. Pilot oil has fully shifted the bucket control valve. The oil delivery from drive pump (15) flows into the right body of the main control valve. The oil delivery flows through center bypass passage (3) to the bucket control valve. Since the spool in the bucket control valve is fully shifted, center bypass passage (3) is blocked. All of the oil delivery from the drive pump flows to the head end of the bucket cylinder. No oil flows to negative flow control orifice (9) and no negative flow control pressure is created in center bypass passage (3). Since no negative flow control pressure is sent to the drive pump regulator, the drive pump regulator moves the swashplate of the drive pump toward the maximum angle position. The output flow of the drive pump is increased since no negative flow control pressure is created in center bypass passage (3).Fine Control Operation
Illustration 6 g01210692
Bucket control valve (fine control)
(3) Center bypass passage
(21) Parallel feeder passage
(22) Port
(23) Spool
(24) Passage
(P) Pilot pressure When the joystick for the bucket is in the NEUTRAL position, spool (23) is in the NEUTRAL position. The oil delivery from the drive pump flows through center bypass passage (3) to negative flow control orifice (9). When the joystick for the bucket is partially moved from the NEUTRAL position in order to perform a fine control operation, pilot pressure (P) enters the control valve at the pilot port. Pilot pressure shifts spool (23) slightly to the left. The movement of spool (23) partially