Four-way Open-center Hydraulic Valve

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When a valve is designed to use a constant-flow source of fluid, the valve does not have its cont.rolling edges covering their corresponding port edges. Instead, each port edge is uncovered in the centered valve position. This type of valve is then said to be underlapped or open-centered as shown by Fig. 1.15. When the valve spool is centered or in the null position, the constant-flow supply is equally divided, and one-half of the supply Bows through each side of the valve with little restriction by the valve orifices. The size of the orifices and their openings are matched. to the amount of Bow supplied so that the pressures PI and P 2 are very low when the valve spool is in the null position. Pressure and flow are provided to the piston actuator by displacing the valve 8pool from this null position. The controlling orifices thereby throttle or restrict the flow being discharged from one side of the valve, at the same time restricting the flow into the valve on the opposite side. This movement of the valve spool not only diverts the flow to the desired side of the piston bu t also causes the pressure of the fluid supply to increase as necessary to move the piston. In this way, the valve controls the pressure of the constant-flow source.

Four-way Open-center Hydraulic Valve

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