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Spray Nozzle Engineering Information

 

Nozzle Type

Typically full cone nozzles have the largest size droplet followed by flat spray nozzles and hollow cone nozzles. This trend applies equally to hydraulic and air assisted nozzles, however, air assisted nozzles provide very fine droplets that are smaller in size than traditional hydraulic nozzles.  For a better description of the characteristics of various types of spray nozzles, click here to go to the nozzle index page.

 

Flow Rate

Flow rate has a direct effect on droplet size. An increase in flow rate will increase the droplet size; similarly, a decrease in flow rate will decrease droplet size.

 

Example: A 150 gpm hollow cone nozzle at 10 psi has a larger droplet than a 100 gpm hollow cone at 10 psi. Similarly, a 50 gpm full cone nozzle at 7 psi has a smaller droplet size than a 120 gpm full cone nozzle at the same pressure.

 

Pressure

Pressure has an inverse effect on droplet size. An increase in pressure will reduce the droplet size, whereas a reduction in pressure will increase the droplet size.

 

Example: A 1 gpm flat spray nozzle has a larger droplet at 30 psi than at 60 psi. Similarly, a 10 gpm full cone nozzle has a smaller droplet size at 40 psi than at 10 psi.

 

Of the factors affecting flow rate, the most influential is pressure. Theoretically, the flow rate varies in correlation with the square root of the pressure, neglecting all other factors. Therefore, to compute flow rates other than those tabulated in the catalog, the following formula may be used (or use our automated flow calculator online by clicking here):

 

Q₁ and P₁ are the known flow rate and pressure.
Q₂ is the resulting flow rate for the desired pressure P₂.

 

 

If you need to calculate the pressure to achieve a specific flow rate, you can use a variation of the same formula:

 

P₁ and Q₁ are the known pressure and flow rate.
P₂ is the resulting pressure for the desired flow rate Q₂.

 

 

Temperature

Temperature influences a liquid's viscosity, surface tension, and specific gravity, which in turn can affect spray nozzle performance.

 

Liquid Properties

Viscosity and surface tension increase the amount of energy required to atomize the spray. An increase in any of these properties will typically increase the droplet size.  Virtually all droplet size data supplied from Lechler is based on spraying water under laboratory conditions. The effect of liquid properties should be understood and accounted for when selecting a nozzle for a process that is droplet size sensitive.

 

Viscosity

Viscosity is probably the most significant of all liquid properties because it can vary over an extreme range. Liquid viscosity resists surface formation. If the viscosity is great enough, a nozzle may produce a mass of filaments instead of a spray. Liquid viscosity is remarkably sensitive to temperature. Thus, liquid viscosity has a significant effect on all of the spray characteristics.

 

Specific Gravity

The main effect of the specific gravity of a fluid being sprayed is on the flow rate of the nozzle. The lower the specific gravity of a liquid, the higher the velocity through the nozzle, and vice versa. Thus, for lower specific gravity, the flow rate is larger than for liquid with a higher specific gravity at the same pressure.

 

 

 

Example: For a fluid with a specific gravity of 1.2 the flow rate would only be about 90% as compared to the flow of water which has a Specific Gravity of 1.

 

Surface Tension

Surface tension is an important physical property affecting surface formation, and makes the liquid resist breaking into droplets. The main effect of surface tension is on the spray angle and droplet size of the sprayed fluid as well as the spray distribution.

 

Spray Angle

Spray angles have an inverse effect on drop size. An increase in the spray angle will reduce the droplet size, whereas a reduction in spray angle will increase the droplet size.  Click Here to use our automated spray nozzle coverage and header layout calculator.

 

Example: A 3 gpm flat spray nozzle with a 50° spray angle has a larger drop size than a 3 gpm flat spray nozzle with a 110° spray angle at the same operating pressure.

 

Impact

The impact or impingement of a spray is measurable, and should be taken into consideration in many applications. For more specific impact information consult with Lechler.  As a general rule, the narrower the spray angle, the greater the impact over a given area.

 

Nozzle Wear

Nozzle wear is denoted by an increase in the  nozzle flow rate and the subsequent deterioration of spray performance.  A reduction in system operating pressure is often an indication of increased nozzle wear, especially when positive displacement pumps are used.

 

Flat fan axial nozzles exhibit a narrowing of the spray pattern with wear. Other types of spray nozzles reveal a loss in spray uniformity within the spray pattern - though without a noticeable change in pattern size.

 

Nozzle Materials

Nozzles are available in many problem-solving materials.  To spray corrosive fluids or for operation in corrosive environments, choose from a variety of chemically and thermally resistant materials, which include stainless steels, titanium, and Hastelloy; or corrosion resistant plastics, such as PVC, PP, PVDF, POM, and PTFE.   To meet high wear and corrosion resistance requirements, common materials for nozzles include stainless steel, ceramic, tungsten carbide, Stellite, and silicon carbide.  They are also available in precision injection molded materials such as PVDF.