Valves control the flow and the pressure of fluids in a mechanical system. Hydraulic valves do the same thing with hydraulic liquids in a hydraulic system. Hydraulic valves are available in a wide variety because valves are used in almost every industrial setup and different industries have different valve requirements. These valves range from simple models, which shut off and turn on the supply of liquids, to control valves. They are very precise and are used extensively in advanced motion control systems.
With increasing modernization, electronics are used extensively in valve technology. This has led to a decrease of error and greater efficiency in hydraulic operations. Previously hydraulic valves and valve component parts were expensive and difficult to replace in the event of a breakdown. However, technology has changed this and hydraulic parts are cheaper now. Some varying types of hydraulic valves that are used extensively are: fluid reversing valves, Italian valves, control valves, angle valves, sequence valves, directional valves, directional control valves, spool valves, pressure relief valves and hydraulic actuated valves.
Angle valves let the liquid in at an angle, thereby allowing maximum flow to the hydraulic circuits. Sequence valves are designed to administer and monitor the sequence of hydraulic circuits. Directional valves are made to steer the fluid to the selected passages. Directional control valves are used to direct the fluid to the selected actuator. This kind of valve is generally stackable and has one valve for each hydraulic cylinder and one fluid input which supplies all of the valves in the stack. Spool valves are actuated by rotary or piston-like spools which move back and forth to cover and uncover ports in the housing. Pressure relief valves are used in various places in hydraulic machinery. The primary function of these types of valves is to remove any excess upstream pressure. For example, pressure relief valves are used to help prevent any overloading on hydraulic cylinders and are used to maintain pressure for brakes on the return circuit.
When you are choosing hydraulic valves you should consider the compatibility of valve size, pressure, rating, ports, media temperature, flow coefficient, and connection type. There are assorted connection types for hydraulic valves. Some have internal or external threads for inlet or outlet connections and others can use a bolt flange, clamp flange, union connection, tube fitting, butt weld, and socket weld.