What is the single most important thing should we understand about the role of the nozzle in a pressure washer?

The nozzle does not create the pressure in and of itself. The pressure washer pump creates a specific amount of flow. By damming the flow with nozzle, you create the pressure—much like when you put your thumb over the end of a garden hose to create a more powerful stream of water. The nozzle is part of a system and must be properly sized to be correctly paired with the flow of the pressure washer. Putting on too small a nozzle can over-pressurize the pump and cause problems. Putting on too large a nozzle lowers the pressure, meaning a loss of efficiency and cleaning power.

With no nozzle, only inlet water pressure (approximately 50 psi) will flow through the spray gun. Also, if a nozzle is sized too small, the machine will create more pressure—and if too large, less pressure.Pressure (psi), flow rate (gpm), and nozzle orifice (size) are related by a fairly complicated algebraic formula.

Q: Is there a top reason why a nozzle might fail?

A: Ordinary flat tip nozzles don’t really fail. They wear out, causing a loss of pressure and efficiency, or they clog. Clogging is the biggest problem for nozzles. Rotary nozzles are another matter. They can fail if the ceramic seat or tip cracks