320C and 322C Forest Machines Hydraulic System Heel Hydraulic System Caterpillar


Heel Hydraulic System
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Illustration 1g00804146

(1) Pilot line

(2) Line

(3) Line

(4) Heel cylinder

(5) Main control valve

(6) Return line

(7) Center bypass passage

(8) Center bypass passage

(9) Heel control valve

(10) Spring

(11) Orifice

(12) Load check valve

(13) Spring

(14) Negative flow control orifice

(15) Pilot control valve (boom and heel)

(16) Parallel feeder passage

(17) Return passage

(18) Pilot line

(19) Negative flow control line

(20) Pilot oil manifold

(21) Left pump

(22) Right pump

(23) Pilot pump

The oil delivery for the heel hydraulic circuit is supplied by right pump (22) only.




Illustration 2g00697166

(9) Heel control valve

The oil delivery from right pump (22) flows through center bypass passage (8) in main control valve (5) to heel control valve (9). The oil delivery from left pump (21) flows through center bypass passage (7) in main control valve (5). Illustration 1 shows the main control valve when only the heel hydraulic circuit is activated.

When the hydraulic activation control lever is in the UNLOCKED position, the oil delivery from pilot pump (23) flows through pilot oil manifold (20) to pilot control valve (15). When the joystick for the heel is moved to the HEEL CLOSE position, pilot oil flows through pilot control valve (15) and pilot line (1) to heel control valve (9). The pilot oil pressure shifts the spool in the heel control valve against spring (13). The pilot oil on the other end of the spool in the heel control valve flows through pilot line (18) and pilot control valve (15) to the hydraulic tank.

Since the spool in the heel control valve is fully shifted, center bypass passage (8) is blocked. None of the oil delivery from the right pump flows to negative flow control orifice (14) and no negative flow control pressure is created in center bypass passage (8). Since no negative flow control pressure is sent through negative flow control line (19) to the right pump regulator, the right pump regulator moves the swashplate of the right pump toward the maximum angle position. The output flow rate of the right pump is increased and flows through parallel feeder passage (16), load check valve (12), heel control valve (9) and line (3) to the head end of heel cylinder (4) .

Since the oil delivery for the heel hydraulic circuit is supplied by the right pump only, the negative control pressure in center bypass passage (7) is high. Left pump (21) remains at the destroked position.

Reference: For more information concerning the negative flow control operation, refer to Systems Operation, "Negative Flow Control".

The return oil from the rod end of the heel cylinder flows through line (2), orifice (11) in heel control valve (9), return passage (10) and return line (6) to the hydraulic tank. Orifice (11) restricts the return oil from the rod end of the heel cylinder.

The HEEL OPEN operation is similar to the HEEL CLOSE operation.

When the joystick for the heel is moved to the HEEL OPEN position, pilot oil flow from pilot control valve (15) flows through pilot line (18) to the heel control valve. The spool in the heel control valve shifts against the force of spring (10). The oil delivery from the right pump now flows to the rod end of the heel cylinder.

When the joystick for the heel is in the NEUTRAL position, springs (10) and (13) maintain the spool in the heel control valve in the NEUTRAL position. The oil flow from the head end and the rod end of the heel cylinder is blocked.

Information System:

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