When it comes to pressure washing, the nozzle plays a pivotal role in determining the system operational state and effectiveness in cleaning. While the pump in most pressure washers delivers a constant flow rate, the nozzle controls how much kinetic energy is imparted on the water (measured as a resulting pressure) by the system; furthermore, the nozzle controls the shape and size of the water spray, as well as the average droplet size. Understanding nozzle sizes and reading a pressure/flow nozzle chart is critical to maximizing efficiency and effectiveness, without causing damage.

Pressure Washer Nozzles Determine Pressure, Not Flow Rate

Positive displacement pumps, the standard in pressure washing applications, produce a fixed flow rate determined by the pump's design. This flow remains constant, regardless of downstream restrictions. In PDP applications, restrictions in the system flow path result in pressure drops, proportional to the restriction characteristics, while flow rate remains constant. However, nozzles determine the pressure at which that flow exits the system. Because water is incompressible, a smaller orifice - combined with constant flow - will imply that water must move more quickly through the orifice, foe conservation of mass to be obeyed through the system. The nozzle size does not change the pump’s output flow rate; it only modifies how energetically water passes through the orifice.

Reading the Pressure/Flow Nozzle Chart

Manufacturers provide pressure/flow charts to help users pair nozzles with their machine’s specifications. These charts show the relationship between nozzle size, pressure (PSI), and flow rate (GPM).

1. Identify your machine's rated GPM (e.g., 4 GPM).

2. Locate the desired PSI for the task (e.g., 2500 PSI), and find your system’s flow rate in chart field.

3. Cross reference the Nozzle size (far left) from the column (specified by the desired pressure) and the row (specified by the system flow rate).

For a given flow rate, a given nozzle size will result in a given pressure value. It is critical that the pressure washing system maximum design pressure is not exceeded by selecting a too-small nozzle, as this will result in immediate, substantial system damage, and an extremely unsafe situation anywhere near the equipment. Always know what pressure your system will operate at, and always have a pressure gauge installed, so be sure.

Types of Nozzle Spray Patterns

In addition to size, nozzles vary in spray patterns, affecting how the pressurized water interacts with surfaces. Common spray types include:

• 0° (Red): Concentrated stream for maximum impact on hard surfaces. There is almost no practical application for this nozzle and will almost guarantee damage in most applications.

• 15° (Yellow): Narrow fan spray for heavy-duty cleaning. This is a highly effective nozzle spray pattern for rinsing and high-pressure applications.

• 25° (Green): Wide fan spray for general cleaning and rinsing. A 25° fan spray is ideal for distributing a cleaning solution over a wide area; however, the outer edges of the fan are far more susceptible to wind-driving effects (reduced range, inconsistent application).

• 40° (White): Gentle spray for delicate surfaces. This is a very wide nozzle, comparable to the 25° nozzle, with similar applications.

• Soap (Black): Most pressure washers come with a black “soap” nozzle. This nozzle actually combines a very wide fan (45 to 60 degrees) and a larger orifice, reducing the pressure of the cleaning solution stream, while maximizing the width of the spray fan.

Avoiding Common Pressure Washer Misconceptions

To clarify: the nozzle does not regulate the flow rate delivered by the pump. The pump's positive displacement design ensures a constant flow, regardless of the nozzle's restriction. Instead, nozzles provide a restriction, which combined with the incompressible nature of water, results in water passing through the nozzle at a higher rate of speed, compensating for the reduced cross-sectional area of the orifice. Selecting a nozzle that is too small will result in system pressure exceeding the safe operational range of the pressure washing system, while a nozzle that is too large will result in system pressure being reduced all the way to a gentle stream, which would be insufficient to obtain desirable power washing results.

Practical Tip for Significant Efficiency Gains in Power Washing

Frequent nozzle changes are common when washing a house or other large surfaces. To save time and improve efficiency, consider using a "J-rod" nozzle attachment, which combines multiple nozzle sizes and spray patterns into a single tool. This simplifies switching between patterns and pressures, making the cleaning process faster and more convenient. Bonus points for having multiple J-rods, each tailored for a specific application. This is easily the cheapest, most functional accessory for a pressure washing system. By treating pressure washer nozzles as tools to shape and regulate pressure and spray patterns, you can tackle a wide variety of cleaning tasks effectively and safely.

For example, a 4.0 GPM pressure washing system, paired with a size 25 nozzle, results in a nozzle pressure of just 100 PSI. Furthermore, a nozzle size of 5.0 results in a pressure of 2,500 PSI, while a 4.0 size nozzle results in a pressure of 4,000 PSI. Without a full set of nozzles spanning a wide range of orifice sizes, each at various fan angles, a pressure washing system remains extremely limited.

A Useful Heuristic from Empirical Data

Given that the system flow rate is constant for any given pressure washing system, the nozzle size needed to achieve a specific pressure output can be determined with a simple formula:

Nozzle Size = 63.23 multiplied by the system flow rate divided by the square root of the desired pressure. For example, if a driveway is to be cleaned using 2,500 PSI, and the system flow rate is 4.0 GPM, then the necessary nozzle would be 63.23 x (4.0/sqrt (2500)) which equals 63.23 x 0.08 and thus, 5.06. Since nozzles are sized in 0.5 increments, select a size 5.0 nozzle, and the resulting pressure will closely approximate 2,500 PSI.

It is worth noting that the coefficient (63.23) arises because of the particular units chosen for the calculation (GPM and PSI). If a flow rate is given in any units other than Gallons Per Minute, or if a pressure is given in any units other than Pounds Per Square Inch, this empirical formula would require a different coefficient to remain valid.

Professional Service Makes a Huge Difference

At Surface Work, we’ve mastered the art of pressure washing through years of dedicated service to Virginia Beach and its surrounding areas. We’ve perfected the ideal pressure and fan combinations for every type of exterior surface material, ensuring fantastic results every time. When it comes to removal of green algae, mold, and other organic growths, the soft washing is a game-changer.

Don’t leave your home’s exterior to guesswork—contact Surface Work today and enjoy peace of mind knowing the job is being done right by a veteran who loves washing houses. From Bay Colony to Acredale and Chic’s Beach to Red Mill, Surface Work has served neighborhoods all across Virginia Beach. Chances are, someone in your area would happily recommend us. Contact Surface Work today.