NOZZLE SELECTION GUIDELINES

Why Nozzle Selection is Important

Spray nozzle designs provide specific flow, pattern, and droplet size. Each combination of variables is ideal for achieving a specific goal, such as cooling, coating, or cleaning. The engineered specifications of each nozzle ensure a complete spray system with multiple components, such as pumps, filters, valves, and piping, will operate effectively and efficiently.
Not considering the whole picture of the system when selecting a nozzle could result in poor performance.

Criteria for Selecting a Nozzle

Spray Patterns

Fan

Fan nozzles are often your best choice for wetting, coating, or cleaning in conveyor belt applications. Examples include belt cleaning, suppressing coal dust on a conveyor, and coating molds with lubrication.

A fan-style nozzle can provide you with the most optimal results when a high-impact force is necessary for cleaning or other applications. The SPN series and narrow-angled NF nozzles will provide a large impact force while generating relatively low flow rates.

Full Cone

Full Cone Whirl

Full cone spray pattern provides great coverage results if you are looking for even distribution over a packed bed. Rain Simulation and Foam-Control applications provide even distribution over specific surface areas using Full Cone nozzles.

Both MaxiPass® nozzles are designed with an S-style vane for significant free passage, while the other Full Cone series utilize a disc with smaller areas that could trap particulates in the water.

Full Cone Spiral

If you are looking for gas cooling or want the liquid to react in a process with a smaller droplet size, the Spiral Full Cone nozzle gives you outstanding results.

Hollow Cone

Small droplet sizes perform better in gas cooling applications, and a full cone nozzle may not create enough small droplets.

Misting

The small droplet size is ideal for when complete evaporation is needed. Misting nozzles can provide a low flow rate that gives optimal results for scientific or pharmaceutical applications, where a small dosing pump is used.

Misting nozzles can also produce a high flow rate with a small droplet size requirement (i.e., area humidification header). Other misting nozzles without atomizing air can create smaller droplets (MWH, misting header).

Straight Jet

Straight Jet nozzles can be very useful for a wide variety of applications. They are often used in washing applications and other situations that call for concentrated flow and high impact. An example of this is the HydroWhirl® Orbitor tank cleaning machine. The HydroWhirl Orbitor uses the long throw and high impact generated by straight jets to clean various tank sizes with difficult residue.

The Straight Jet nozzles can produce the highest impact and longest throw out any nozzle type. They have few limitations, and nozzles such as the LP & PSR use compact designs to make applications possible when space is at a premium.

Air Atomizing

Air atomizing nozzles atomize fluids by combining liquid and compressed air/gas at low pressures to form a very fine spray. They can create either a fan or cone spray pattern depending on the design of the nozzle. There are two methodsof mixing fluid and air: internal and external.

Internal mixing –liquid and air streams come together inside the nozzle and are mixed, and they exit through the same orifice. The streams are not independent; airflow changes will affect the liquid flow

External Mixing -the air and liquid streams exit the nozzle independently through each orifice.Air and liquid flow rates can be independently controlled, allowing precise fluid metering.

Automatic

Automatic nozzles are used for intermittent spraying solutions. These nozzles apply precise volumes of sprayon the target. The spray coverage is uniform, and the amount of overspray is reduced so that material waste is minimal.

The spray flow rate can be electronically controlled by pulsing the sprays while adjusting the ON versus OFF dwell time ratio within each cycle. Pulsing at high frequency allows the average flow rate to be adjusted while maintaining constant fluid supply pressure and the appearance of continuous, uniform coverage. This flow control process is known as Pulse Width.

Droplet Size

Droplet size is often critical. Many processes such as gas scrubbing depend on exposing the maximum possible liquid surface to a gas stream. Other applications require that the droplets be as large as possible, such as when the spray must project into a fast-moving gas stream. Exposing the maximum surface area requires breaking the liquid into droplets as small as possible.

To get an idea of how this works, imagine a cube of water with a volume of 1 gallon. This cube has a surface area of 1.6 ft2. If we split it in two, we expose some inner surfaces and increase the total surface area to 2.1 ft2.

Atomizing the liquid into spheres 1 mm (1,000 microns) in diameter would increase the surface area of this gallon of liquid to 244 ft2. A nozzle produces a range of droplet sizes from the solid-liquid stream. Since it is inconvenient to list all the sizes produced, droplet size (in microns) is usually expressed by a mean or median diameter.

Detail of Relative Drop Size by Nozzle Series

Spray Coverage

Four terms are commonly used to describe spray coverage.

Spray Angle

(A) The included angle of the spray is measured close to the nozzle orifice. Since the droplets are immediately acted upon by external forces (gravity and moving gases, for example), this measurement is useful only for determining spray coverage close to the nozzle. The spray angles listed for nozzles in this catalog are angles at the nozzle, measured at the nozzle's design pressure, highlighted in each chart of flow rate vs. pressure.

Actual Spray Coverage

(B) The actual coverage at a specified distance (D) from the nozzle.

Effective Spray Angle

(C) The angle calculated from the actual coverage (B) at a distance (D).

Theoretical Spray Coverage

(E) The coverage at a distance (D) if the spray moved in a straight line.

Detail of Spray Dimensions 2

Flow Rate

The required flow rate depends on the specific application and pressure across the nozzle (ΔP). Most applications have general rules of thumb for the flow ranges, but many require some field-testing trial and error.

ΔP = Supply pressure at nozzle inlet / external pressure at the nozzle outlet

Higher ΔP = higher flow rate
Lower ΔP = lower flow rate

Material Considerations

Some factors that influence the nozzle material selection process are:

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