Overview: Directional control valves, such as check valves and reversing valves, are used to control the direction of oil flow in order to start, stop, advance and retract the actuator. Cartridge type, these valves without a separate valve body, the spool, valve sleeve and other components of the cartridge inserted in the prefabricated hole in the cartridge block, the cartridge body plays the role of the valve body and the pipeline, Through the block channel will be several components will be inserted together into a loop. There are usually on-off valves, proportional valves, servo valves and digital valves. After switching valve can only be set in the state of work. Proportional and servo valves can be connected to the input signal or proportional control system parameters. Digital valve side with digital signals directly control valve action. Hydraulic system actuator (such as hydraulic cylinder, hydraulic motor) in the work, you need to start, brake, change direction and adjust the speed of movement and adapt to changes in external load, so there must be a set of institutions to control and Regulated hydraulic components, usually with a control valve to complete. It does not work outside, only for the control of the implementation of components, to meet the performance requirements of the host. 1, the control valve according to their functional classification (1) direction control valve, such valves, such as one-way valve and valve, used to control the direction of oil flow in order to achieve the implementation of components to start, stop, forward and back. (2) Pressure control valves, such as relief valves, pressure reducing valves and sequence valves, are used to control the pressure in the hydraulic system to control the force, torque or working sequence required by the actuator. (3) flow control valve, such valves, such as throttle and speed control valve, used to control the size of the fluid flow in the hydraulic system in order to achieve the required speed of the actuator. 2, the control valve according to their connection classification (1) pipe connection, pipe valve threaded connection, it is directly in series with the system of piping, do not need a dedicated connecting plate. (2) Plate connection, plate valve requires a dedicated connecting plate, the valve screw mounted on the connecting plate, the pipe connected to the connecting plate, the valve plate installed in front of the board behind the tubing. (3) flange connection, flow greater than 300L / min, with flange connection. Weld the flange at the end of the pipe and connect it to the valve body with a screw. (4) integrated block, manifold is a common hexahedron, surrounded by the side with the actuator connected to the fittings, the other three to install valve components. The manifold within the channel with the valve connected to form a different basic circuit. Above and below the manifold block and block connection between the surface, a few blocks stacked with long bolts, both to form the entire hydraulic system. Its features are: compact structure, less tubing, easy handling and maintenance. (5) Stacked valve, stacked valve is a standardized hydraulic components, the valve body will be stacked together by bolts, stacked valves directly connected to each other to form a hydraulic system. Each stack valve functions as a control valve and acts as a passage body. Its features are: compact structure, less tubing, small size, light weight, no pipe connections, pressure loss, save a lot of tubing and fittings. (6) Cartridge type, these valves without a separate valve body, by the spool, valve sleeve and other components of the cartridge inserted in the prefabricated hole in the block, the cartridge body plays the valve body and tube The role of the road, through the block within the channel will insert a few components together, you can loop. It is characterized by: very suitable for large flow situations. 3, control valve classification according to their general operation manual, pedal, motor, pneumatic, electric and hydraulic and other methods, and sometimes several forms of combination. 4, according to the classification of work pressure by the control valve in the hydraulic system working pressure is divided into: low pressure valve, medium pressure valve and high pressure valve. 5, according to the control principle usually has on-off valve, proportional valve, servo valve and digital valve. After switching valve can only be set in the state of work. Proportional and servo valves can be connected to the input signal or proportional control system parameters. Digital valve side with digital signals directly control valve action.