The directional valve is a directional control valve with more than two flow forms and more than two oil ports. It is a valve to realize the communication, cut-off and reversing of hydraulic oil flow, as well as pressure unloading and sequential action control. The valve is controlled by the direction of relative movement between the valve core and the valve body. There are rotary valve type and slide valve type. It is divided into two positions and three positions according to the number of working positions of the valve core in the valve body; It is divided into two-way, three-way, four-way and six-way according to the number of oil circuits connected to the valve body; The movement modes of operating the valve core include manual, motorized, electric, hydraulic, electro-hydraulic, etc.

The items of solenoid valve are the most, which mainly includes the following items:

1. Working reliability

It refers to whether the electromagnetic iron can be reliably reversed after power on, and can be reliably reset after power off. The solenoid valve can work normally only within a certain flow and pressure range. The limit of this operating range is called the commutation limit.

2. Pressure loss

Because the opening of the solenoid valve is very small, there is a large pressure loss when the liquid flows through the valve port.

3. Internal leakage

At different working positions and under the specified working pressure, the leakage from the high-pressure chamber to the low-pressure chamber is the internal leakage. Excessive internal leakage will not only reduce the efficiency of the system and cause overheating, but also affect the normal operation of the actuator.

4. Commutation and reset time

The commutation time of AC solenoid valve is generally 0.03 ~ 0.05s, and the commutation impact is large; The commutation time of DC solenoid valve is 0.1 ~ 0.3s, and the commutation impact is small. Generally, the reset time is slightly longer than the commutation time.

5. Commutation frequency

The commutation frequency is the number of commutations allowed by the valve in unit time. At present, the commutation frequency of solenoid valve with single electromagnet is generally 60 times / min.

6. Service life

The service life of the solenoid valve mainly depends on the electromagnet. The service life of wet electromagnet is longer than that of dry electromagnet, and that of DC electromagnet is longer than that of AC electromagnet.

7. Hydraulic clamping of slide valve

The hydraulic clamping phenomenon of the slide valve exists not only in the directional valve, but also in other hydraulic valves, which is more prominent in the high-pressure system. In particular, the longer the residence time of the slide valve, the greater the hydraulic clamping force, so that the thrust (such as electromagnet thrust) of the moving slide valve can not overcome the clamping resistance, so that the slide valve can not be reset.

The reasons for hydraulic clamping are that some dirt enters the gap and makes it difficult for the valve core to move, and some are that the gap is too small and the valve core expands and sticks when the oil temperature rises. However, the main reason is the radial uneven hydraulic pressure caused by the geometric error of the slide valve pair and the change of concentricity. In order to reduce the radial unbalanced force, the manufacturing accuracy of the valve core and valve hole should be strictly controlled. During assembly, it should be in the form of straight cone as much as possible. On the other hand, opening an annular pressure equalizing groove on the valve core can also greatly reduce the radial unbalanced force.