ZSF Prefill Valves

The Bosch Rexroth ZSF Prefill Valves are high-flow, pilot-operated check valves designed primarily for use in hydraulic press circuits (sizes 32 up to 200).1 Their main function is to allow free flow (prefill) of low-pressure fluid from a reservoir into the main cylinder of a press as the ram moves down, which saves energy and speeds up the cylinder’s idle stroke. The valve works as a large check valve, opening with a minimal pressure difference to allow massive flow to pass into the cylinder.3 When the high-pressure press stroke begins, the valve closes and is held shut by the system pressure, but it can be opened by a pilot pressure (X-port) to quickly and gently decompress and empty the cylinder after the work stroke. The series offers both basic valves (ZSF) and versions with an integrated directional valve for the pilot control (ZSFW), ensuring controlled opening and closing behavior.