A brief discussion on various control valves

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This post was last edited by Wu Xiaozhen on 2017-4-18 at 13:38. Components used in hydraulic transmission to control liquid pressure, flow rate, and direction. Those that control pressure are called pressure control valves, those that control flow rate are called flow control valves, and those that control on/off status and flow direction are called direction control valves. 　　Direction control valve: Classified by purpose into check valves and directional control valves. 　　①Check valve: It allows fluid to flow in one direction only within the pipeline, blocking flow in the reverse direction. 　　②Directional control valve: Changes the on/off state between different pipelines; classified as two-position, three-position, etc., based on the number of working positions of the spool within the valve body ； Classified into two-way, three-way, four-way, five-way, etc., based on the number of channels under control ； Based on the driving method of the valve core, they can be classified as manual, mechanical, electric, hydraulic, etc. 　Flow control valve: It regulates the flow rate by adjusting the area of the throttle opening between the valve spool and the valve body, as well as the local resistance generated there, thereby controlling the movement speed of the actuator. Flow control valves are classified into 5 types based on their purpose. 　　①Throttle valve: After adjusting the area of the throttle opening, it enables the speed of actuators for which changes in load pressure are not significant and low requirements are placed on motion consistency to remain essentially stable. 　　②Throttle valve: It maintains a constant pressure difference between the inlet and outlet of the throttle valve when the load pressure changes. In this way, once the throttle area is set, regardless of how the load pressure changes, the speed control valve can maintain a constant flow rate through the throttle, thereby keeping the movement speed of the actuator stable. 　　③Flow divider valve: A valve that enables two actuators connected to the same oil source to receive an equal flow rate, regardless of the load, is known as an equal-flow divider valve or a synchronous valve ； A valve that distributes flow in proportion is a proportional flow divider valve. 　　④Collecting valve: Its function is the opposite of that of a distributing valve; it distributes the flow rate entering the collecting valve in proportion. 　　⑤Shunt collector valve: combines the functions of both a shunt valve and a collector valve. 　　Pressure control valves are classified by function into relief valves, pressure reducing valves, and sequence valves. 　　①Relief valve: It enables the hydraulic system to remain at a constant state once the set pressure is reached. The relief valve used for overload protection is called a safety valve. When the system fails and the pressure rises to a critical level that could cause damage, the valve opens to allow overflow, thereby ensuring the safety of the system. 　　②Pressure relief valve: It enables the branch circuit to achieve a stable pressure that is lower than the oil pressure in the main circuit. Depending on the pressure function they control, pressure regulators can be further divided into constant-value pressure regulators (which provide a constant output pressure), constant-difference pressure regulators (where the difference between the input and output pressures is constant), and constant-ratio pressure regulators (which maintain a certain ratio between the input and output pressures). 　　③Sequence valve: It allows one actuator (such as a hydraulic cylinder or hydraulic motor, etc.) to operate first, and then enables other actuators to operate in sequence. 　　In the late 1960s, electro-hydraulic proportional control valves were developed on the basis of these various hydraulic control valves. Its output values (pressure, flow rate) can vary continuously with the input electrical signal. Depending on their function, electro-hydraulic proportional control valves are classified into electro-hydraulic proportional pressure control valves, electro-hydraulic proportional flow control valves, and electro-hydraulic proportional direction control valves, among others.