How to position nozzles in a spray bar

When positioning nozzles on spray bars we need to consider what the desired outcome is. If a perfectly even distribution of fluid over the target is required then the process is as follows:

1. Measure the desired target width. When covering a conveyor then this would be width of the conveyor.

2. Measure the height at which you want to position the spray bar. Normally there will be a range at which it is feasible to position a spray bar. If there is a wide range, select the height that would be easiest and use this for the calculations below. You can always move it up or down a bit to get the spray coverage spot on.

3. Decide on the number of spray nozzles you want to use. To get a vaguely even spray you will need at least 3 nozzles on a spray bar. The more nozzles you use the smaller the spray angle for each nozzle required and the closer you can get the spray bar to the target.

4. Calculate the minimum required spray angle of each nozzle. This can be calculated by dividing the total width required by the number of nozzles. This is the width each nozzle is responsible for covering. If we use the height you selected in point 2 we can now calculate the minimum required spray angle of each nozzle using basic trigonometry.

For example, for a bar that is positioned 200mm above a target that is 1000mm in width with 4 nozzles the required minimum spray angle would be calculated as follows:

• Each nozzle needs to cover 250mm of the target (1000mm / 4)

• The half spray pattern is a right-angle triangle with sides of 125 mm and 200 mm.
• Using trigonometry: TAN (125/200) = 0.625.
• The angle is 32 degrees, which is half the overall spray angle.
• Therefore, the minimum required spray angle is 64 degrees.

5. Adjust for overlap. The minimum required spray angle represents a situation where each spray pattern from each nozzle just about touches the next. We need to overlap the spray patterns somewhat to compensate for the fact that there is less fluid delivered at the edges of the pattern. We also need to compensate for the effects of gravity which tends to narrow down the spray pattern from the one we see very close to the nozzle.

If we want a 30% overlap then, in effect, each nozzle needs cover 30% more width. In the example above, instead of 250mm, each nozzle now needs to cover 325mm rather than 250mm. If we then use this in our trigonometry we can calculate the new required spray angle. Which would be 80 degrees.   

Note: when we overlap spray patterns in this way it is standard practice to angle the spray patterns so they don’t actually hit each other. Anything passing under the spray bar will get the full delivery of fluid. 

6. Consider the edges. Spray patterns tend to deliver less fluid at the edges. To counteract this, overlapping spray patterns, as explained in point 5, can help ensure even distribution. However, at the edges of the spray bar, where there are no additional nozzles, the solution is to over-spray. This means deliberately allowing the last 20-30% of the spray to fall off-target, ensuring that the target area receives an even application of fluid.

7. Consider spacing. For most spray bars, nozzles should be spaced evenly along the bar. Start by considering any over-spray required at the edges, as discussed in point 6. Once the positions for the first and last nozzles are determined, calculate the distance between them. Divide this distance by the number of remaining nozzles plus one to determine the spacing.

For example, if you have 3 nozzles between the first and last nozzle and the distance between them is 1 metre:

• Divide the 1 metre by 4 (3 remaining nozzles + 1), resulting in a spacing of 250 mm between nozzles. If there are 6 nozzles in total, divide the 1 metre by 5 (4 nozzles + 1), which gives 200 mm spacing.

Conclusion

Correctly positioning nozzles in a spray bar involves careful measurement and calculation to ensure even fluid distribution and optimal performance. By following these steps, you can effectively design a spray bar system that meets your needs, whether it's for precision coating, cleaning or moistening applications.