![]() An advantage of the open-center system over the closed-center system is that the continuous pressurization of the system is eliminated. When the pump is in this fully compensated condition, its internal bypass mechanism provides fluid circulation through the pump for cooling and lubrication.A relief valve is installed in the system as a safety backup. The pump is fully compensated (near zero flow) when normal system pressure is attained. When pressure approaches normal system pressure, the compensator begins to reduce the flow output of the pump. The compensator automatically varies the volume output. ![]() If a variable displacement pump is used, system pressure is controlled by the pump’s integral pressure mechanism compensator. A relief valve acts as a backup safety device in case the regulator fails. If a constant delivery pump is used, the system pressure is regulated by a pressure regulator. The means of controlling pump pressure varies in the closed-center system. This system differs from the open-center system in that the selector or directional control valves are arranged in parallel and not in series. The three actuators are arranged in parallel and actuating units B and C are operating at the same time, while actuating unit A is not operating. The valve automatically returns to the neutral position and to open center flow.Ĭlosed-Center Hydraulic SystemsIn the closed-center system, the fluid is under pressure whenever the power pump is operating. When the actuating mechanism reaches the end of its cycle, the pressure continues to rise to a predetermined pressure. The manually engaged and pressure disengaged type of selector valve is similar to the valve previously discussed. This action reopens the open center flow and allows the system pressure to drop to line resistance pressure. ![]() The system pressure remains at the relief valve set pressure until the selector valve is manually returned to the neutral position. The relief valve unseats and allows the fluid to flow back to the reservoir. Then, the actuating mechanism reaches the end of its operating cycle, and the pump output continues until the system relief valve relieves the pressure. First, the valve is manually moved to an operating position. One type is both manually engaged and manually disengaged. Several types of selector valves are used in conjunction with the open center system. Operation of the system following actuation of the component depends on the type of selector valve being used. ![]()
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