Abstract: The improved traveling spray assembly and washing method includes a vertical header pipe mounted on tracks that run the length of the bank of collector plate electrodes. The header bears a plurality of nozzles directed to spray washing fluid onto the collector plate electrodes for their washing. A horizontal supply pipe is mounted along the top or the bottom of the electrostatic precipitator and extends to about the mid-point of the bank of collector plate electrodes. The horizontal supply pipe is connectable outside the electrostatic precipitator to a source of washing fluid. A pair of pivotally-connected pipes next are provided. One of the pipes is pivotally connected to the end of the supply pipe at the mid-point of the bank of collector plate electrodes and extends to a position opposite the supply pipe at either the bottom or top of the electrostatic precipitator. The other pipe extends back to the side of the supply pipe and is pivotally-connected to the header pipe.