How To Select a Proper Cartridge Pre-Filter for Your Application

Definitions
Nominal rating - a nominal rating for a filter is an arbitrary value assigned by the filter manufacturer and is expressed in terms of a percentage retention of a given challenge media such as ISO standard test dusts or glass beads. The value may represent the percentage of the entire distribution of particles that is removed from the test fluid or the percentage of a specific sized particle.
Nominal filtration ratings are often used when comparing the performance of depth and non-membrane filters.

Absolute rating - An absolute rating is the size of the smallest particle retained by a filter with a stated efficiency, such as 99 %, under defined test conditions. Absolute ratings are typically applied to membrane or high performance non-woven filters.

Filter Sizing
As a general rule, the smaller micron rating for a filter is better. However, there is a trade-off; flow capability usually drops off as the micron rating gets smaller, especially if the water has a lot of sediment. Veolia offers an innovative depth filter using patented Z.Plex* technology that provides the following advantages without compromising flow.

The depth filters using Z.Plex technology provide:
• Up to twice the life of conventional depth filters
• Up to 50% lower pressure drop
• Up to 100% greater dirt holding capacity with superior
SDI reduction.

A 1 micron filter using Z.Plex technology will provide 1 micron filtration at an equivalent pressure drop or life span of a conventional 5 micron filter. Similarly, a 5 micron filter using Z.Plex technology will provide 5 micron filtration at an equivalent pressure drop of life span of a conventional 10-micron pressure drop filter.

Be aware that in certain situations, a smaller filter rating is not always better. For example, in many well water applications, sediments cause flow restriction through
the filter. The best solution for this type of problem is to install a larger rated filter (i.e., sediment filter) upstream of the smaller micron rated filter to remove the larger
pore-clogging particles and retain good flow rate. In such situations, it is common to see two or three sediment prefilters in the water flow, starting with the higher micron
rating to remove the larger particulate, followed by lower micron rating filters. An example of a typical process flow is to first filter the water through a 20-micron sediment prefilter, then a 5-micron, and finally through a 1-micron or a sub-micron filter. This process extends the life of all filters and, most importantly, the downstream membrane elements.


* Source: VEOLIA TB1148EN.docx May-22