The document provides instructions for disassembling and assembling a piston pump (hydraulic fan) on an excavator. It outlines 30 steps to disassemble the pump, removing components like the head, port plate, bearings, pistons, and shaft. It then lists 27 steps to reassemble the pump, replacing components in the reverse order and taking precautions around spring-loaded parts. The instructions specify using the proper tools and cleaning parts thoroughly during assembly.