How to select the correct filter size for the spray tip you're using and the material being applied.
Selecting incorrect filter sizes can result in tip blockages. Filters act as a defence for the spray tip and prevent any debris from passing through the hose, gun or tip.
The first filter in a system is usually the suction filter or the strainer in the bottom of a hopper or pump. The suction filter/strainer is to stop anything that isn’t the material you're spraying from entering the pump. Next in the system is the main pump filter. The pump filter is usually found on the manifold on the side of the machine (although this varies on different machines). The purpose of the pump filter is to do the majority of the filtering. The last filter in the system is the gun filter. Not all guns will have filters. Usually, for higher viscosity material you won’t need a gun filter. The gun filter is the last line of defence against tip blockages.
Filters are measured in mesh sizes. The higher the number of the filter mesh size the smaller the holes.
How do I know what size filter I need?
If your material includes a data sheet look out for what filter size the manufacturer suggests you use.
You can also work out what filter you need based on the spray tip that you’re using. Take a look at the second two numbers on the spray tip. This tells you the size of the spray orifice in thousandth of an inch. Simply convert the orifice size to mm, if the particles in the material are over this size they have the potential to block the spray tip. You need to make sure the filter you’re selecting has smaller holes than particles in the materials you’re spraying.
For example, let's take a Graco 517 spray tip. It has an orifice of 17 thousandths of an inch (thou). Converted to mm this is 0.43. You need to pick a filter with smaller holes than 0.43mm. In this case you could use 60 or even a 30 mesh filter.
If you need help picking the correct spray tip read our blog here.
Below is a mesh to millimetre conversion chart.
If you use a filter that is too small you run the risk of over-filtering the material. This will lead to the filter becoming blocked quickly. When it’s fully blocked the pressure build from the pump and will blow a hole through. If filtered too finely you run the risk of removing parts of the material you’re wanting to spray. This is why you shouldn’t over spec your filter and you use the correct filter for spray tip you are using.