1. Basic functions
The pilot valve controls the stroke, direction and main control valve of the spool. The spring at one end of the main control valve spool performs the basic function of the pilot valve, and the output pressure (secondary pressure) of the pilot valve is supplied to the other end of the main control valve spool.
In order to perform this function correctly, the pilot valve has the following functions.
① The oil inlet P supplies oil from the hydraulic pump.
② The oil outlet sends the pressure of the oil inlet to the end of the spool of the control valve ③ The oil tank oil port T controls the above output pressure.
④ The valve core connects the oil outlet to the oil inlet or the tank oil port ⑤ The pilot valve controls the output pressure, including the spring acting on the above valve core
2. Main components
The function of the excavator function spool is to receive the oil pressure from the hydraulic pump at port P, and switch the oil circuit to determine whether the oil pressure of port P can be output to the port, or whether the spool output can determine the pressure output.
The spring acting on the spool determines the output pressure.
Spring deviation changes, the push rod is inserted and slides in the plug.
The displacement of the push rod is changed by the cam and the adjusting nut. The displacement is controlled by the pedal. The cam can be used as a fulcrum to tilt the pedal in any direction.
The spring acts on the valve housing and the spring seat and returns the push rod to the zero discharge position as much as possible, ensuring that it is reset to the intermediate position.
The operator feels the correct sense of control through the response of the spring.
3. Operation
Based on the hydraulic circuit diagram shown in Figure 1-91 and the cross-sectional diagram shown in 1-90, the operating principle of the pilot valve will be explained.
(1) The force of the spring in the middle position of the pedal determines that the output pressure of the pilot valve will not be applied to the spool. Therefore, the spool is pushed by the spring to the position of the port in Figure 1-92. Because the output port is only connected to the tank port T, the output port pressure and the tank pressure become equal
(2) Pedal in the inclined position
When the push rod is pushed down, the spool moves downwards. Then, the oil port P is connected to the oil port, and the oil supplied by the pilot pump flows through the oil port to generate oil pressure.
When the pressure increase at the port is equal to the spring force set by the tilt pedal, the pressure is balanced with the spring force. If the pressure at the port increases above the set pressure, port P is disconnected from port and port T will be connected to port. If the pressure at this port decreases
If it is lower than the set pressure, port P is connected to port, and port T will be disconnected from port.
In this way, the secondary pressure always maintains a stable value. Moreover, when the pedal is inclined more than a certain angle, the upper end of the valve core contacts the inner bottom of the push rod, and the output pressure is connected to the oil port P.
