To understand how to better use your pressure washer you have to understand how different types of nozzles work and how varying the angle of the spray pattern changes the impact of the nozzle.
In this example, a 13HP pressure washer putting out 4.2 GPM and 3,500 PSI will generate 13.07 foot pounds of impact using a zero degree nozzle (color: red). Most of time, it is impracticable to clean using a zero tip nozzle. Most people use a 15 degree nozzle (color: yellow). Calculating the impact in foot pounds you can see that it drops to 3.92, or only 30% of the full impact delivered by a zero degree nozzle. Using a 40 degree nozzle (color: white), drops the impact to only 12 percent of the maximum delivered by a zero degree nozzle.
This explains why rotary nozzles, such as the Dirt Killer nozzle, are so effective. They are really turbines with a zero degree nozzle that are turning thousands of times per minute. So using a rotary nozzle you come the closest to getting the maximum cleaning impact from your pressure washer – typically three times what you get with a 15 degree nozzle.