YA00049668 Original Excavator Return Line Check Valve for Hitachi EX1900-6

The part number YA00049668 is marked as VALVE in Hitachi's original system, which is a check valve/back pressure valve or a small valve block assembly with a bracket for the return oil pipeline (often appearing in customs declaration information as a set with support components such as 4646790 and 4336875, classified as valve HS 8481). It is mainly used on the return oil pipe, oil/hydraulic return branch or engine side return oil collection pipe of the engine turbocharger to prevent oil/air backflow and establish necessary back pressure during shutdown. This valve is commonly found in Hitachi's large mining models and related power units, such as EX3600-6 (LD), EX1200-6 (LD), EX1900/EX1800-6 (LD), etc.

As a valve component installed on the return side of the engine, its core function is to only allow one-way flow of oil/gas towards the fuel tank or limit the return oil pressure to a safe window, avoiding backflow that may cause oil shortage in the turbine bearings, oil splashing, or system leakage. The original valve body is usually made of carbon steel/ductile iron forgings or high-strength aluminum alloy. The sealing surface is precision ground or equipped with grinding gaskets, and oil resistant fluororubber (FKM) or composite sealing structure is used to resist heat return oil (common operating conditions range 80-130 ℃+) and pulse. Structurally, it is common to have a spring-loaded valve core and a conical/spherical seal. Some versions are made into an assembly with an installation bracket, and the correct flow direction is ensured by the direction of the arrow; The interfaces are mostly pipe threads (PT/G) or flange surface seals, and the opening pressure/back pressure value and leakage rate are controlled according to Hitachi drawings from the factory, making it easier to achieve long-term non leakage and non jamming than general parts.

The maintenance points are simple but crucial: the direction cannot be reversed, the sealing surface cannot be damaged, and the system must be clean. During daily/regular maintenance (it is recommended to observe every 250 hours), check whether there are fresh oil stains on the valve body and joints, and whether the valve body has been deformed by impact; If there is abnormal bubbling/splashing at the return oil port, leakage on the turbine return oil side, or abnormal fluctuations in the return oil back pressure, priority should be given to checking whether the valve is stuck or the sealing surface is scratched. Release pressure and clean the surrounding sediment before disassembly. After disassembly, check for scratches on the valve core and seat, rust and fatigue on the spring, and whether the O-ring/gasket is flat or cracked; When installing new parts, make sure to see the arrow on the valve body facing towards the oil tank, and that there are no old gasket residues or burrs on the contact surface. Tighten it in the prescribed order and with torque (to avoid twisting the valve body on one side too tightly and causing micro seam oil leakage).