Kubota U20-3, Руководство по ремонту

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U20-3, U25-3 WSM Hydraulic system (Mechanism section)
IV -M-2
A.Features of hydraulic system
No Function Detail
1 Arm regeneration. Part of return oil from the arm cylinder rod is allowed to flow to the arm cylinder
bottom, speeding up the arm's crowding and preventing the arm's getting stuck.
2 Redesigned boom anti-drift valve. The minimum boom down speed can be controlled by the main spool, which helps
inch the attachment more finely. (On conventional types, the inching is limited by
the drain circuit's minimum leak amount.)
3 Straight travel circuit adopted. In traveling and moving the front attachment at once, the third pump's flow rate
serves to control the attachment. This circuit is activated once the machine travels
to the right or left and the front attachment is moved.
4 Pilot valve (Kawasaki-made)
redesigned. The vertical stroke is made greater from 5.2 mm to 6.4 mm (to eliminate jerking at
vertical rotation). The secondary pressure is also made higher from 19.5 kgf/cm
2
to 27.0 kgf/cm
2
for improved controllability.
5 Swivel negative brake adopted. Release the lever lock, and the negative brake gets activated to keep the parked
machine even on a slope.
6 Priority throttle of boom-bucket
simultaneous operation. The throttle check valve added between the boom and bucket sections enables
operating the boom and bucket at once.
7 Travel lock for safety. Raise the left operation lever, and oil from the hydraulic pilot pump gets unloaded
and the spring force gets the travel lever locked.
8 Anti-cavitation valve in travel
motor. Cavitation noise can be kept low at stop.
9 Line filter adopted in hydraulic pilot
line. A specific filter is introduced to keep out contamination.