(1) Structure of pilot control valve
(2) Working principle of pilot control valve of Doosan excavator
Working principle 1
1. The center of the operating handle → the working device does not move
①Neutral position of handle
② The oil in ports A and B is connected to the tank through the small hole f in the spool (1)
③The main spool is kept in the middle position under the action of internal spring
④ The working device does not operate.
Working principle 2
2. Action of operating handle → action of working device:
① Move the operating handle to the left
②The disc (5) pushes the plunger (4) to move down
③The positioner (9) also moves down
④The spring (2) pushes the slide valve (1) downward
⑤PPC valve P1 port is connected with the f port on the spool (1)
@Pilot pressure oil flows to port A through control orifice f
⑦ The spool of the main control valve moves to the right, and the B port oil returns to the tank
③The oil from the main pump flows to the working device through this spool
@Working device starts to move
Working principle 3
3. If the handle stroke becomes larger, the working device speed increases
①The stroke of the operating handle becomes larger
②The compression amount of the spring (2) becomes larger
③The spring (2) has a larger force
④Sliding valve (1) Downward movement amount becomes larger
⑤ The flow area of the small hole f port becomes larger
⑥ P1 port pressure increases
⑦The movement amount of the main control valve spool becomes larger
③ The flow to the working device becomes larger
③The working speed of the working device is accelerated
