Maeda MK0003, Service Manual, Page: 94 / 348

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7.4.3 HYDRAULIC VALVE (COUNTER-BALANCE VALVE)
When supplied through port A, the hydraulic oil pushes check valve (3) to open it, and flows in port A’ on the inlet side
of the hydraulic motor. On the other hand, the hydraulic oil enters chamber D through choke hole C, and allows the
spool valve (2) to slide in the rightward direction by overcoming the force of spring (4). Consequently, the return side
oil of hydraulic motor flows in through port B’, flows through the body (1) and opening E of spool valve (2), and returns
to port B to drive the hydraulic motor.
When the hydraulic oil is supplied through port B, the motion of the above-mentioned parts will be in the reverse
direction, and thus the hydraulic runs in reverse.
Subsequently, as the hydraulic oil in port A is shut off from the pressurized state, the spool valve (2) so far sliding
rightward will try to return in the rightward direction owing to the force of spring (4). In this stage, because of the
squeezing effect of choke hole C, the oil in chamber D controls the leftward returning speed of spool valve (2).
Concurrently, the hydraulic motor is forced to rotate by the inertial force, even if the hydraulic oil in port A is shut off. In
this process, the spool valve (2) switching speed and the shape of dent, controls the return oil so that the hydraulic
motor is smoothly stopped.