Many filter users look at their cartridge filters, see that they are dirty, and immediately change the filters. Although on the surface this logic appears to be good, it is probably costing you money.
Cartridge filters are designed to remove particulate matter in the body of the filter as well as on the surface. The particulate that is deposited on the surface of the filter (commonly known as Filter Cake) acts as a filter in its own right and as the depth of the filter cake increases the filter becomes more efficient. In effect the dirt is filtering out the dirt.
By allowing filter cake to build up on the filter the life of the cartridge filters will also be extended, thus reducing the filtration cost for each liter filtered.
You can take advantage of this life extension by installing a pressure gauge both before and after your Filter Housing and measuring the pressure of the liquid before it goes through the filter element as well as after the liquid has been filtered. The difference between the readings on both gauges is referred to as differential pressure.
You will note that the longer the filter element is in the housing the greater the differential pressure will become because greater force is needed to move the liquid through the cartridge. When the differential pressure reaches 20-30 psi you should change the filters.
If you allow the pressure to exceed the 20-30 psi differential you will run the risk of channeling particulate through the body of the filter thus bypassing the filter and negating the purpose of the filter. When channeling occurs the differential pressure actually decreases.