Filtration is critical for protecting the sprayer’s components and to reduce the potential for nozzle blockages. Generally, filters are placed before the pump (suction), after the pump (pressure) and before the nozzles (often on boom sections).

There is an ISO standard for the colour of filter screens (related to their mesh size), but unfortunately not all manufacturers use this ISO colour code. When ordering a filter, it is important to state the mesh size required for the screen, not just the colour.

Tip

• Ideally, filters should be located where they are easy to access. Locate filter bowls facing downwards and have a manual ball valve on the bowl so the filter is easier to service.

Suction filters

The suction filter is located between the tank outlet to the suction side of the pump. 

Suction filters for centrifugal pumps, should ideally have a 16-mesh screen or similar, which is the most appropriate filter screen size to reduce the chance of any foreign material getting caught in the pump’s impeller.  Finer filter screens may cause restriction.

Suction filters for diaphragm pumps, should ideally have a 30 or 50-mesh screen, which are the most appropriate filter screen sizes to protect positive-displacement pumps.

Pressure filters

Ideally, the main pressure filter will be installed after the pump but before any of the plumbing components (such as the flow meter and regulating valves).  It can be very useful to use pressure filters that can have a manual ball valve mounted on the bottom of filter bowl.

The main pressure filter should have either 80 or 100-mesh screens (matched to the suggested screen size for the nozzle being used, which are suitable for both centrifugal and diaphragm pumps. It is important to have a pressure relief valve installed between the pump and main pressure filter when using diaphragm pumps.

Boom-line filters

Boom-line filters should also have 80 or 100-mesh screens. However, the mesh size can be changed to suit the nozzle orifice size or formulation type according to the recommendations on the product label.

It is best to mount the boom-line filters out on the boom sections. They should beplumbed into the spray line at a point as close as practical to where the spray line connects to the boom line.

Nozzle filters

The mesh size for nozzle filter screens, where fitted, should match the nozzle orifice size. Most nozzle manufacturers will recommend filter sizes to match particular nozzles.

For many situations, it may be preferable that nozzle filters are not installed. Generally, if there is a problem with products blocking nozzles, the source of the problem will be filtration upstream from the nozzles. 

Nozzle filters can accumulate material on the filter screen due to the low liquid flow rates that occur through a single nozzle. At low flow rates the filter screen can strip components out of the formulation (detectable as a film on the screen).

This generally does not occur when the same mesh-size screen is used on the boom filters due to the higher flow rates of liquid that will flow to a whole boom section compared to a single nozzle.

However, from the operator’s perspective, it may be better to have an individual blocked nozzle that can be easily seen, rather than a series of nozzles that has restricted flow due to a partially blocked line filter.

Tips

• The main reasons for having a suction filter on a centrifugal pump are to protect the pump by taking coarse foreign matter out of the spray solution and to reduce the amount of work the main pressure filter must do.

• You may need to match the mesh size of the pressure filter screen to the product being used, according to information on the product label, or to the nozzle orifice size.

• All filters should be mounted so the filter bowl is facing down. This way any foreign material falls out when the bowl is removed. It is practical to have a manual ball valve at the base of the filter bowl so the filter can be flushed clean without the bowl having to be removed.

• Have a full set of gaskets or O-rings on hand. Operators can waste a lot of time trying to install filter bowls with swollen gaskets or O-rings. It is useful to place swollen O-rings and gaskets in direct sunlight for several hours (or days) to see if they shrink back to their normal size