User Guide

How A Nozzle Works

Now that we know what a nozzle is supposed to do, let’s see how

it does it.

But before we do, let’s take a look at the cutaway showing the

functional parts of a typical Delavan nozzle (Fig. 1). The flow rate,

spray angle and pattern are directly related to the design of the

tangential slots, swirl chamber and orifice.

FIGURE 1 Cutaway view of a Delavan nozzle.

First, a source of energy is needed to break up the oil into small

droplets. Therefore pressure is supplied to the nozzle, usually

from a motor-driven pump at 100-150 psi (Fig. 2). But pressure

energy alone doesn’t do the job. It must first be converted to

velocity energy and this is accomplished by directing the

pressurized fuel through a set of slots which are cut in the

distributor at an angle, or tangentially, to create a high velocity

rotation within the swirl chamber. At this point, about half of the

pressure energy is converted to velocity energy.

As the oil swirls, centrifugal force is exerted against the sides of the

chamber, driving the oil against the orifice walls, leaving a void or

core of air in the center. The oil then moves forward out of the orifice

in the form of a hollow tube. The “tube” becomes a cone shaped

film of oil as it emerges from the orifice, ultimately stretching to a

point where it ruptures and throws off droplets of liquid.

How a Nozzle Works

FIGURE 2 How a nozzle works.