Understanding the differences between different airless spray tips and choosing the right one to suit your purpose should be a fairly straight forward process. The first point of reference in most cases is to check if the manufacturer of the paint you plan to spray has provided a technical data sheet. A coating technical data sheet is different to the MSDS or Material Safety Data Sheet. The TDS or Technical Data Sheet typically provides information about preparing the surface to suit the coating, applying the coating and drying times etc. Many major coating manufacturers also include information in their TDS about recommended spray painting equipment and if they suggest airless spraying there will often be a recommended airless spray tip size specified.
One important aspect of airless spray tip theory when selecting any airless spray tip is the relationship between orifice size which determines flow and the airless spray tip angle which will determine the width of the spray pattern. A simple way of looking at this is to consider for example a certain airless spray tip orifice size, lets say a 0.017" which theoretically should flow around 1.17 litres per minute. (Airless spray tip flow rates are usually specified with water at a given pressure, typically around 2000 psi) Now a 0.017" tip is available in a wide range of angles providing fan patterns between 2 inches wide through to 16" wide or larger. The important thing to consider is that the flow rate for all 0.017" tips should be the same no matter what the fan pattern width is so theoretically the airless spray gun will need to move faster with a narrow 2 inch wide 0.017" airless tip than it will need to be moved using a 12 inch wide 0.017" tip to achieve the same amount of film build.
So.. if a paint manufacturer specified a 10 to 12 inch wide 517 airless spray tip for their paint but you need to use a narrower 6 to 8 inch wide spray pattern using the same coating it may be preferable to reduce the orifice size to an 0.015 tip and select a 315 instead of a 317. This relationship can be demonstrated mathematically. The table below compares difference by dividing the flow rate by the fan pattern width. A 517 has approximately 0.12 litres per minute per median inch of spray pattern width and a 315 has approximately 0.13 litres per minute per median inch of spray patter width. By comparison a 317 airless spray tip has approximately 0.2 litres per minute, per median inch of spray pattern width meaning that this would need to be moved faster that the 517 airless tip to achieve the same amount of film build.
|Tip Size||Flow L/pm||Median Fan Width Inches||L/pm flow per inch of fan width||Tip No|
Another important aspect to cater for is that wider spray pattern airless spray tips can be more prone to blockages as the orifice is a longer and much narrower slit compared to a shorter and wider opening of a narrow airless spray tip orifice.