To better understand the intention of the different types of nozzles we look at the impact power against a surface, even though the psi (pressure per square inch) and gpm (gallons per minute) are the same the way in which the water is projected towards the surface is different. With the nozzle 8 inches from the surface you can see the impact power that each nozzle has against the surface.
1. Pencil Jet: Other known as the 0 degree fan spray is the most agressive spray which can penetrate into a surface 10 times more than what a regular fan spray nozzle. Being the most aggressive this nozzle should only be used for specific pressure washing applications, the most used to clean in areas that are beyond the reach of a standard fan spray, for example: the high eves of a house where you can’t reach with a ladder.
2. Fan Spray: This is the most common nozzle used for pressure washing, this nozzle is most effective for general cleaning, such as siding, decks or other soft to medium hardness materials. This nozzle also allows for a much faster cleaning due to the fact that it spreads the water out in wide fan at less impact power. The downside is that this nozzle doesn’t have the impact power that the other nozzles offer
3. Rotary Nozzle: Other known as the Dirtblaster Nozzle, the spray that this nozzle creates takes the impact power that you would get out of the pencil jet spray along with the wider spray that you would get out of a fan nozzle. Though this nozzle is not the most aggressive it allows the water to penetrate 7 times as much than the fan spray nozzle. This nozzle can also clean at a much faster rate due to the surface area and the impact power. Though the Rotary Nozzle is very beneficial in cleaning it should only be used on hard surfaces such as, steel, concrete, brick, etc.
Now that you understand the difference between each of the nozzles and what they offer you can choose what one might be ideal given your cleaning application. Keep in mind to use caution with each of the types of nozzles and to decrease the risk of damage always test them on a small area before tackling an entire job.