Each filter cartridge specification and pricing page has one or more flow rate graphs at the bottom of the webpage. These charts are also on the second page of the corresponding datasheet. Below is a copy of the chart from the LOFTREX.

Seven retention sizes are listed and you can see how the differential pressure increases as the flow rate increases.

**Example**. The 10 micron cartridge
will have a 0.73 PSI differential at a 6.6 GPM flow rate; at 8.8 GPM the
differential pressure increases to about 1 PSI.

This differential pressure (ΔPSI) is
based upon the initial "clean state"; as particles become trapped
within the filter cartridge, the open area available decreases and
therefore the corresponding differential increases exponentially. Testing is performed in a laboratory with
ambient water and with a 10" cartridge; so if you have a 20"
cartridge, the differential pressure values would be half of what is
shown in the graph; OR to state it another way, a 20" cartridge has
the capacity double the 10" size for a given differential
pressure. Example: A 20" 10 micron LOFTREX
cartridge would have a clean differential pressure of 0.73 PSI for
13.2 GPM *OR* only 0.36 PSI for 6.6 GPM.

The "clogging curve" illustrates the exponential increase in differential pressure as the media becomes clogged. This is a reflection of the "increase in efficiency" related to the clogging of open area and ability of retaining finer particles.

In practice this means that, assuming a consistent particle size and volume, the amount of time required to become 75% clogged is only ½ the time required for the initial 50% clogging. Stated another way, once you reach 50% clogged, the clogging rate doubles.

Besides the physical cost of replacement filter cartridges, you should consider the frequency of replacement with regards to labor costs, down time and annual disposal costs. Then consider using a more expensive cartridge which will provide you with higher particle loading capacity, thus reducing the frequency of change outs and your disposal costs. Usually the more expensive "engineered" cartridges end-up being a more cost effective product than the less expensive versions that are replaced more frequently; it's just a little harder to quantify.