Vales are used to regulate the flow of liquid through the lines of the pressure washer. Valves in the industry will have many different names but the basic construction boils down to only a few designs. There are ball valves, gate valves, needle valves and a variation of the ball valve that uses a ball and seat.
Ball valves are used to turn the flow of water on or off. While many people will use them to reduce or regulate flow this is not a preferred use for this valve as the flow of liquid in a partially open/closed valve will be exposed to the seals which will cause premature failure of the valve. Construction of a ball valve includes a valve body which will be open on two ends and have an opening in the top for the valve handle stem to go through. Inside the body there is a machined ball with a hole through it that has a round curved seal on each end. When the valve is open the fluid flows through freely, when the handle is rotated the valve handle stem turns the ball to the area that is not machined out and the flow stops. Three-way, four-way, and five-way ball valves use a similar design but will have the ball machined out at a right angle which allows for more selection options.
Gate valves are typically used to regulate flow. Typically gate valves are used on the inlet to machines to regulate the amount of water to the pump. This is important when upstreaming chemical (injecting prior to the pump) or when the amount of head pressure or flow rate into the pump is too great and impacts performance. A gate valve will have a body that is open on each end and a flat plate (gate) in the center that is controlled by a valve handle stem with a knob on top. The valve handle stem will have threads on it like a bolt, this allows for the valve to have the amount of opening controlled by the positon of the handle by turns.