A hydraulic valve properly directs the flow of a liquid medium, usually oil, through your hydraulic system. The direction of the oil flow is determined by the position of a spool. A hydraulic system can only function as per requirements by using valves. The required size is determined by the maximum flow of the hydraulic system through the valve and the maximum system pressure.
Hydraulic valves are available in a variety of sizes and according to multiple International Standards. Hydraulic valves are available with many different mounting styles: e.g. mounting in pipe lines, with threaded connection as cartridge valves, subplate mounting or flanged mounting. Hydraulic valves are subdivided into three main categories: directional control valves, pressure control valves and flow control valves. All valves operate a different function in the hydraulic system.
1.Directional Control Valves
Directional control valves can control the start, stop and change in direction of flow of a pressure medium (i.e. hydraulic oil). They are also called as Switching Valves. The function of Directional Control Valve is to start, stop and change in direction of flow of a pressure medium.
2.Pressure Control Valves
Every pressure control valve switches or controls at a predetermined pressure setting. The switching pressure is generally a variable setting on the valve itself. A change in position of the pressure control valve (i.e. open or closed) occurs either gradually or suddenly. Pressure shut-off valves and pressure sequence valves are hydraulic valves with a fixed throttle whereas relief and reducing valves are hydraulic valves with a variable throttle.
3.Flow Control Valves
Flow control valves manage the flow by decreasing or increasing the opening at the throttling point. This helps to determine speed of movement for the actuators. The simplest design for a flow control valve is a needle or longitudinal slot mounted in the pipeline and connected to a screw that adjusts the opening at the throttling point. These are called throttle valves due to the fixed throttle, which changes the actual flow through the valve at varying loads.