The electro hydraulic solenoid valve is a two-stage control cartridge solenoid valve. The pilot stage functions as a two-way solenoid valve, which is equivalent to a relief valve. The main spool is a three-way cartridge valve, as shown in Figure 1.
electro hydraulic solenoid valve 1
A pilot stage solenoid valve determines the opening of the main spool, as shown in Figure 2.
electro hydraulic solenoid valve 2
When you energize the pilot level solenoid valve, the solenoid valve moves to the left position. The main oil pressure acts on the solenoid valve through the damping hole. At this point, the electromagnetic force generated by the solenoid coil cuts off the main oil pressure. As the hydraulic oil amount increases, the main oil pressure builds up more at the lower end of the main spool. The main spool then overcomes the spring force and moves upward. Consequently, the main oil pressure aligns with the control oil pressure, and the hydraulic system’s executing element performs its action.
When the main oil pressure increases or decreases, the main spool reaches a new equilibrium point under the action of electromagnetic force. This operating principle is similar to that of pilot-operated pressure reducing valves.
When the pilot stage solenoid valve de-energizes, the electro-hydraulic solenoid valve moves to the right position. The electromagnetic force disappears, and the spring force resets the main spool. This action connects oil port B with oil port C. The control oil pressure then flows back to the tank through the small holes, while the main oil pressure returns to the tank through the damping holes R1 and R2.
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