Hydraulic Valve (Counter Balance Valve) - Kubota U20-3 Workshop Manual

U20-3, U25-3 WSM

[3] Hydraulic valve (counter balance valve)

When the pressure oil is supplied through the port A, the pressure oil pushes open the check valve (3)
and flows into the inlet-side port A' of the hydraulic motor. At the same time, the pressure oil flows
through the choke hole C into the room D and slides the spool valve (2) to the right, overcoming the
force of spring (4). As a result, the hydraulic motor return oil flows in through the port B', passes
through the opening E of the main body (1) and spool valve (2) and returns to the port B. These pro-
cesses make the hydraulic motor rotate. When the pressure oil is supplied through the port B, the
above-mentioned processes are reversed and the hydraulic motor rotates reversely.
When the pressure oil supplied through the port A is made unpressurized, the spring force works to
return the spool valve to the left. At this time, the oil in the room D controls the speed at which the
spool valve returns to the left, utilizing the choking effect of the choke hole C. Even if the pressure oil
supplied through the port A is made unpressurized, the hydraulic motor continues rotating using an
inertial force. At this time, the return oil is gradually controlled through the sliding speed of the spool
valve and the helix shape, thus stopping the hydraulic motor smoothly.
Hydraulic system (Mechanism section)
IV-M-44