Selection of Hydraulic Electromagnetic Reversing Valve
Electromagnetic reversing valve, also called solenoid valve, is a conversion element between hydraulic control system and electrical control system. It uses the suction force of the energized electromagnet to push the spool of the slide valve to move and change the oil flow to realize the reversing, starting and stopping of the actuator. According to the structure of the electromagnet, it is divided into AC type, DC type, and self-rectifying type; according to the specification of the working power supply, it is divided into AC 11OV, 220V, 380V。
The contraindications for selecting electromagnetic reversing valve are as follows:
1. The electromagnet in the solenoid valve has a DC type, an AC type, and a self-rectifying type, and the structure is divided into a dry type and a wet type. Various electromagnets have different characteristics such as suction characteristics, excitation current, maximum switching frequency, mechanical strength, impulse voltage, pull-in impact, and reversing time, so appropriate electromagnets must be selected. The special electromagnet has safety explosion-proof type and pressure-resistant explosion-proof type. When used in high-humidity environment, it should be treated with tropical heat, and when used in high-temperature environment, attention should be paid to insulation.
2. The slide valve function of the solenoid valve must not fail to meet the requirements. Solenoid valves have many spool functions, and there are differences between front and reverse installation when leaving the factory, so it is necessary to check whether the spool functions are consistent with the requirements when using them.
The mid-position spool valve function of the reversing valve is related to the safety of the actuator when the actuator is stopped. The internal leakage and back pressure must be considered and fully demonstrated from the circuit. In addition, the maximum flow value will vary greatly with the spool valve function, so attention should be paid.
3. Do not ignore the switching time and transition position function of the solenoid valve. The shape of the spool of the reversing valve affects the opening area of the spool, the change law of the displacement of the spool, the switching time of the valve and the action of the actuator at the transition position must be carefully selected.
The switching time of the reversing valve is affected by the type of electromagnet in the solenoid valve and the structure of the valve, the control pressure and the control flow of the electrohydraulic directional valve. The flow rate is controlled by the throttle valve, and the switching time of the electro-hydraulic directional valve can be adjusted. In some circuits, such as in the hydraulic system of walking equipment, a reversing valve is used to switch the flow and adjust the flow rate. When selecting this type of reversing valve, attention should be paid to its throttling characteristics, that is, the relationship between flow rate and pressure drop under different spool displacements.
4. The pressure and flow rate of the reversing valve should not exceed the rated pressure and flow rate on the manufacturer's sample. Otherwise, the hydraulic clamping phenomenon and the influence of hydraulic power often cause poor movement. Especially in the hydraulic cylinder circuit, the oil return flow is different when the piston rod is extended and retracted. The oil return flow is larger than the output flow of the pump when the piston rod is retracted.
It should also be noted that when the four-way valve blocks A port or B port and only flows on one side, the rated flow rate will be significantly reduced. Therefore, when determining the diameter of the valve, not only the reversing valve itself is considered, but also the pressure loss has a great influence on the circuit efficiency of the hydraulic system, so when determining the diameter of the valve, not only the reversing valve itself is considered, but also the pressure loss of all valves in the circuit, the internal resistance of the oil block, the pipeline resistance, etc. must be considered comprehensively.
5. The pressure of oil return port T cannot exceed the allowable value. Because the working pressure of the T port is limited, when the four-way solenoid valve blocks one or two oil ports and is used as a three-way valve or a two-way solenoid valve, if the system pressure value exceeds the allowable back pressure value of the electromagnetic reversing valve, the T port cannot be blocked.
6. The two electromagnets of the double electromagnet solenoid valve cannot be energized at the same time. For the AC electromagnet, the two electromagnets are energized at the same time, which may cause the coil to heat up and burn out; for the DC electromagnet, the position of the valve core is not fixed, causing the system to malfunction. Therefore, when designing the electric control system of the solenoid valve, the two electromagnets should have an interlocking relationship between power on and off.