Genuine Karcher replacement part, this item is sold individually.
This part acts as a seal to keep the oil in the reservoir and the water in the pump form contaminating each other.
It is installed on the piston.

Genuine Karcher replacement part, it is sold individually.
This part along with the piston controls the flow of water through the pump assembly.
This part has a tendency to wear out.
It may be wise to keep a few extra on hand.

Genuine Karcher replacement part, this item is sold individually.
The purpose of the Grooved Ring is to keep the oil in the pump and the water from mixing together.
The piston does move through this part.
This is a wear part, it will need to be replaced ASAP once it is worn.

Genuine Karcher replacement part, this item is sold individually.
The purpose of this part, is to attach the Female Hose Connector to the Piston Guide.
This part is made of plastic and has plastic threads that do wear out.
It may be wise to have an extra one or two on hand.

This is a genuine Karcher replacement part, it is sold individually.
When your pressure washer loses pressure, it probably means you have a bad spill valve.
Also known as an unloader valve.
This part allows water to recirculate in the pump when you're not spraying water and is responsible for most of the pressure-related problems with your pressure washer.

We do have an article and video on "How to Replace the Spill Valve on a Karcher Pressure Washer" on our site. Just go to the front page of our site and click on Repair Center.