Selecting the Right Fluid Nozzle for your Spray Gun
Overview of Air Caps and Fluid Nozzles
Air Caps provide air to break up a coating, while Fluid Nozzles control the amount of fluid that the spray gun will deliver. The amount of material delivered will vary between gravity fed, suction fed, and pressure fed spray guns. In order of fluid delivered for the same nozzle size from the most fluid delivered to the least the order is as follows. Pressure fed with the most fluid delivered, Gravity Fed second, and suction fed third. The air cap used for each of these guns will differ as well and should be adjusted along with the fluid nozzle for optimum finish results. Suction fed spray guns have specific air caps that they require that are different than those used with a pressure fed or gravity fed spray gun. The CFM rating of the air cap determines how much power the air cap will provide in breaking up a coating. The higher CFM rating an air cap has the heavier and/or higher volume of coating the cap will be able to atomize well. A lower CFM air cap will have a better transfer efficiency and less coating waste along with a softer spray pattern but with a decreased ability to atomize coating well. With this general overview of air caps and fluid nozzles we can move on to determining a good size for your application.
Determining the Correct Size of Fluid Nozzle for Your Spray Gun
Pressure Fed Spray gun
- Step 1 – Check your manual for general recommendations of the fluid nozzle size and fluid delivery for each size. This will provide a reference of potential fluid nozzle sizes to consider.
- Step 2 – With a pressure fed spray gun it is important that you try to keep the fluid pressure applied to the pressure pot less than about 20 PSI. If you have more pressure than that applied it is recommended to try a larger sized fluid nozzle so that the fluid nozzle and needle on the spray gun have lower pressure on them and will last longer. If fluid pressure is greater than 20 PSI and you can Increase the fluid nozzle you should. If you are not receiving enough fluid but the fluid pressure is lower than 20 PSI you can increase the pressure up until 20 PSI or you can adjust to a larger fluid nozzle. For an overview of a pressure fed spray gun and pressure tank you can check out this tutorial to get an idea of how to dial the pressure tank in. Overall, it can take a few tries to determine the best size fluid nozzle for your application. It can also help to talk with a equipment provider to see their recommendation of past sizes. Typically a 1.4 MM fluid nozzle is a good starting point for the majority of coatings and if you need more production or coating increase the fluid nozzle size or if you want finer control of the coating and breakup reduce the nozzle size from a 1.4.
Gravity Fed Spray Gun
- Start with the owners manuals recommendation for different coatings and look at the size range for your particular coating. Essentially the heavier a coating the larger the nozzle will need to be and the lighter a coating the smaller the nozzle will be. Most clear coats are sprayed out of a 1.2 or a 1.4mm nozzle for instance. Stains for wood working are sprayed out of a 1.0 MM or a 1.2 MM. Bases for automotive finish are often sprayed from a 1.6 or 1.4 MM nozzle.
- Determine how fine a finish you want – A smaller nozzle will allow for a finer finish pattern (as long as the same air cap is being used) this is because more air will be applied to a smaller volume of coating resulting in a finer breakup. If you want a fine finish stick to the smallest fluid nozzle that you can have the material flow through.
- How thick is the coating ? – A heavy Bodied Coating will require a large fluid nozzle and it will often make sense to start with a 1.6 nozzle. If you need more coating bump the nozzle up and if you need less than reduce the nozzle size this will best be done by doing test passes on your product with the nozzle to determine if the coating is being applied to heavy or light. If you cannot get the gravity fed spray gun to deliver enough coating you will want to consider switching to a pressure fed spray gun. Ultimately finding the right nozzle will require trial and error to see how much fluid flow you want. The best technique is to have a sample product to try a few different nozzle sizes to determine what will work best for your particular coating.
Suction Fed Spray Guns
- Again start with the manual. The manual should give you an overview of ideas to consider. Do be aware that with suction fed spray guns they will typically require larger nozzles than gravity or pressure fed spray guns for the same coating. This is because the suction fed spray gun requires air to move across the coating to pull it through the fluid nozzle. So if you have a nozzle that matches from a gravity or pressure fed outfit I would recommend starting with the fluid nozzle one size above the gravity or pressure set up you have been using.
- Determine how fine a finish you want – The suction fed spray gun will often not be as fine of a finish as a pressure or gravity fed spray gun. If you find your not achieving the finish you want with the suction fed spray gun try reducing the fluid nozzle size or increasing the CFM provided by your Air Cap if this will not work it might be time to consider a gravity or pressure fed spray gun.
- How Thick is the Coating? – If the coating is highly viscous start with a bit of a larger nozzle like a 1.6 MM fluid nozzle. If more coating is needed you should increase the fluid nozzle size. If less is needed you should consider decreasing the fluid nozzle size. You can also increase or decrease the fluid flow to a certain extent by increasing or decreasing air supplied to the suction fed spray gun but this will also cause increased over spray.
If you need help determining a good nozzle for your application we are here to help.