Maeda MK0003, Руководство по обслуживанию, Страница: 104 / 348

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3. When a switching valve is operated
(when the solenoid of negative magnetic proportional reducing
valve is excited)
Since applying the maximum current to the solenoid (SOL10) of negative magnetic proportional reducing valve
(5) causes the secondary pressure to vary (decrease) in commensurate with its current value, the leftward force
acting on flow control spool (2) decreases accordingly.
Consequently, flow control spool (2) moves rightward to open control notch (e) to release the remnant oil to the
tank. At this moment, detecting valve (1) remains unlifted, and thus hydraulic oil does not flow into the parallel
path. Subsequently decreasing the applied current in commensurate with trigger operation degree causes the
secondary pressure to rise, flow control spool (2) to move leftward and control notch (e) to close. As a result, the
hydraulic oil pushes detecting valve (1) to open so that it can flow into the parallel path to drive the actuator.
Further, decreasing the applied current allows the control notch (e) to close fully and the total amount of hydraulic
oil to flow in.
These actions occur in succession to effect the flow control in commensurate with the applied current value.
When the load pressure varies under this condition, flow control spool (2) allows the opening position of control
notch (e) so that the front and rear pressure difference of detecting valve (1) is maintained at a constant level,
and thus the flow rate of supply to the actuator is kept constant regardless of the variation of load pressure.
SOL10
From pilot line
To tank line
Trigger operation
amount
Central bypass path shut off
Actuator
1. Detecting valve
2. Flow control spool
5. Negative magnetic proportional reducing valve
Coil current
Secondary
pressure of pilot
Parallel path
flow rate
Remnant oil