FLUID POWER HANDBOOK
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HYDRAULIC Hydraulic valves, used in conjunction with actuators, are what help make hydraulics unique in its control of force, torque and motion. Valves govern direction, pressure and flow of hydraulic fluid, enabling smooth, safe control of actuators. Valve use can be as simple as a relief valve to protect your pump and actuator. Conversely, the complexity of a hydraulic circuit can be extensive, using a dozen valves per function as can be seen in manifolds. DIRECTIONAL CONTROL VALVES The directional control valve is available in myriad configurations and is named as such if its primary function is to somehow control the path of fluid flow. Directional control valves manage fluid by blocking, diverting, directing, or dumping. Their complexity varies immensely (just like their cost), as does the method of integration. Valve construction runs the gamut from cartridge valves to monoblock valves, or subplate mounted valves to inline valves. Their usage depends on the industry in which they are typically applied.
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The most basic directional valve is the check valve; it allows flow into one work port and blocks flow from coming back through the opposite work port. Alternatively, directional valves can be complex, such as with the pilot-operated valve. A standard spool valve has one directly operated component that controls fluid through the valve. However, as flow increases, the force upon the spool also increases, and these forces can prevent a spool from actuating, as is most often with electric coils. By using a small pilot valve to control the movement of the larger, mainstage spool, the size (and flow) of the valve is nearly limitless. Directional valves are often described by the number of “ways” fluid can travel through them, and also by the positions available to be shifted into. The ways are equal to the number of work ports, so a 4-way valve will have Pressure, Tank and A and B work ports. Positions are equal to the number of positional envelopes. For example, one would describe a doubleacting single monoblock valve as “4-way, 3-position,” or simply a “4/3 valve.” Directional valves are available in
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7/15/19 10:07 AM
