Solenoid valves have the most specifications, mainly including the following:
Operational Reliability: This refers to whether the electromagnet can reliably switch directions when energized and reliably reset when de-energized. Solenoid valves can only operate normally within a certain flow and pressure range. The limit of this operating range is called the switching limit.
Pressure Loss: Due to the small opening of the solenoid valve, a significant pressure loss occurs when fluid flows through the valve port.
Internal Leakage: Internal leakage refers to the amount of leakage from the high-pressure chamber to the low-pressure chamber at various operating positions and under a specified operating pressure. Excessive internal leakage not only reduces system efficiency and causes overheating but also affects the normal operation of the actuator.
Switching and Reset Time: The switching time of AC solenoid valves is generally 0.03–0.05 seconds, with a relatively large switching impact; while the switching time of DC solenoid valves is 0.1–0.3 seconds, with a smaller switching impact. The reset time is usually slightly longer than the switching time.
Reversing Frequency
The reversing frequency is the number of reversals a valve is allowed to make per unit time. Currently, the reversing frequency of a single-electrode solenoid valve is generally 60 times/min.
Service Life
The service life of a solenoid valve mainly depends on the solenoid. Wet solenoids have a longer service life than dry solenoids, and DC solenoids have a longer service life than AC solenoids.
Hydraulic Jamming of Spool Valves
Hydraulic jamming of spool valves is not only present in directional control valves but also commonly occurs in other hydraulic valves, and is more prominent in high-pressure systems. Especially, the longer the spool valve's dwell time, the greater the hydraulic jamming force, to the point that the thrust of moving the spool valve (such as the solenoid's thrust) cannot overcome the jamming resistance, preventing the spool valve from resetting.
The causes of hydraulic jamming include contaminants entering the gaps, making it difficult for the valve core to move; and gaps that are too small, causing the valve core to expand and jam when the oil temperature rises. However, the main cause is radial unbalanced hydraulic pressure caused by geometric errors and concentricity changes in the spool valve assembly. To reduce radial unbalanced force, the manufacturing precision of the valve core and valve bore should be strictly controlled. During assembly, they should be made into a conical shape as much as possible. On the other hand, opening an annular pressure equalizing groove on the valve core can also greatly reduce radial unbalanced force.
