4179171 Excavator Hydraulic Pump Regulator Piston for Hitachi ZX200-5G

Part number 4179171 is the original servo piston (or regulator piston) provided by Hitachi for the hydraulic main pump regulator of excavators such as ZX200-5G. This component is the core executing part of the hydraulic main pump regulator, responsible for pushing the inclined plate under the control of the regulator valve core, changing its inclination angle, and accurately controlling the output flow of the pump. According to the maintenance data of Hitachi ZX200-5G, its hydraulic main pump is a dual variable axial piston pump, and the regulator piston is a key precision component for achieving pump variable control. This part number is mainly suitable for Hitachi ZX200-5G excavators, and may also be applicable to other ZAXIS-5G series models that use the same main pump assembly.

This product is a precision ground alloy steel piston. Its core function is to convert the pilot oil pressure output by the regulator into mechanical displacement, directly driving the main pump swash plate to rotate, thereby infinitely adjusting the plunger stroke and pump displacement. As an original component, its clearance with the regulator valve body hole is extremely small (usually a few micrometers), ensuring the sensitivity and control accuracy of oil pressure response, while also having excellent wear resistance and anti bite properties.

Inspection and replacement: When there are faults such as slow, weak, stuck or abnormal pump noise in the whole machine, after excluding oil quality, filter element, pilot pressure and other issues, if the regulator valve core acts normally but the inclined plate does not respond, it should be suspected that the servo piston is stuck or worn. Simple inspection method: Remove the regulator side cover and observe whether the piston can be easily pushed by hand and returns smoothly. If it is stuck or leaking severely, it needs to be replaced. Attention: Before disassembling the regulator, be sure to release all hydraulic system pressure and disconnect the battery; Precision mating surfaces need to be protected against rust during storage; When replacing the piston, it is recommended to check or replace all seals inside the regulator at the same time