How to Rebuild a Pressure Washer Pump

Rebuilding a pressure washer pump is not an easy DIY project. It requires proper understanding of the schematics of the pump and how each part functions. Improperly rebuilding the pump can either make it not work or have a short life. This article is a general guide to rebuilding one, and is not specifically aimed at rebuilding a specific model.

Tools and Materials

  • Pressure washer pump schematics
  • Pump service manual
  • Replacement parts
  • Hammer
  • Screwdriver
  • Valve pliers
  • Silicone grease

Step 1 – Understand the Pump Design and Schematics

Pressure washer pumps are designed to pump water at a certain pressure – high-pressure pumps usually produce pressures above 150 PSI. The pressure is created by allowing a certain amount of water to flow from the water supply pipes, and out through a nozzle. If you look at the pump schematics, you will find that the device is made out of a system of cylinders and valves. There are also plungers or pistons, that move back and forth to suck water from the inlet valve, and push it to the outlet valve.

Step 2 – Prepare for Reconstruction

In order to dissemble the pump and reassemble it, it is important to get a service manual from the manufacturer. This is usually not contained in the pump kit, but can be downloaded from the manufacturer’s website. Read the entire manual, to get a good understanding of the pump.

Step 3 – Check the Nozzle and Water Inlet Filter

Check the nozzle, and make sure it is the correct size and if it is set to its original setting. If the nozzle is damaged or worn out, remove and replace it. Determine the location of the water inlet filter as well. Using a pair of pliers, remove the filter and clean it. Replace, if it is torn or missing. Reinstall it to the pump.

Step 4 – Inspect the Bypass Valve

Refer to the service manual for the location of the deflector cap and fastening cap. Remove them from the pump. Remove the housing of the thermal relief valve, and pull the bypass valve out of the system. Inspect the bypass valve and the other removed parts. Check for any signs of damage and for proper lubrication. Check the o-rings as well. Any torn o-rings and other damaged parts in the bypass valve should be replaced. Replace the valve itself, if it is worn out. Grease the o-rings before installing in the valve in reverse order.

Step 5 – Inspect the Check Valve

Use a screwdriver and a hammer to tap the valve plate, to remove it from the system. Remove the valve caps, and then remove the entire valve, with valve pliers. Inspect every part of the valve for damage. Replace damaged parts, or replace the entire valve set with a new one. Grease the o-rings and reassemble the valve back to the pump.

The pump system has also other complicated parts inside of it. Refer to the service manual for disassembly and reassembly instructions. When replacing missing or damaged parts, refer to the parts chart included in the manual, for detailed information.