Why does the hydraulic system's spool valve have damping sticking? In a word: contamination!
What is damping sticking? It is when tiny particles reside between the hydraulic valve spool and the valve body, increasing the friction of the valve spool movement. Damping sticking reduces the valve's response, affects production, and increases maintenance costs.
Normally, the radial clearance between the valve core and the valve body of a common reversing valve is between 3 and 13 μm. However, in reality, it is difficult for the valve body to achieve excellent roundness and straightness (this is why servo valves and servo proportional valves install valve sleeves between the valve body and the valve core - for high precision). Therefore, the radial clearance basically changes with the length of the valve core. This affects the friction of the valve core - of course, the cleanliness of the oil will also affect the friction.
If the gap between the valve core and the valve body is invaded by hard particles (such as sand) or soft particles (such as paint and sludge), more force is required to push the valve core. According to test data from Eaton Hydraulics, if a radial gap of a valve core with a diameter of about 3.2mm (1/8 inch) works at 210bar (3000PSI), it takes about 136N (30 pounds) of thrust to move the valve core. But if the valve is operated by electromagnetic force, the electromagnetic force can only provide about 45N (10 pounds) of thrust at most!
This problem is often called silt-lock and is common in valves that are not frequently used and are exposed to contamination. Furthermore, if a silt-locked valve is driven by an AC solenoid, the most likely result is a solenoid burnout. This occurs because the silt-lock valve core prevents the solenoid coil from being fully pulled into the coil. As a result, the coil is magnetized with an inrush current whenever it is energized - because its heat cannot be dissipated. This creates an insulation around the coil windings that burns out and the coil eventually shorts out.
For DC electromagnets, a certain voltage corresponds to a certain current, no matter where the electromagnet spiral tube is relative to the coil. Therefore, it is less likely to burn out. However, if the voltage is connected incorrectly, it may burn out the coil, such as connecting a 12V electromagnet to a voltage of 24V, because the resistance value remains unchanged and the current is twice as much.
It is also very simple to prevent damping from sticking. Keep the oil "clean, cool and dry". "Clean" means adequate filtration system settings to prevent the intrusion of hard particles. "Cool and dry" means that the hydraulic system should not be operated too hot, moisture should not enter, and soft particles such as sludge should be avoided.