There are many types of pre-filters available, being employed in a wide range of applications. As the name implies, pre-filters are generally used early in a process to take the load off more expensive filters further downstream.
Large water systems requiring a reduction of suspended solids often use filtration media using sand, diatomaceous earth or other material capable of removing particles as small as 5 - 10 microns. These filters help prevent fouling in ultrafiltration or reverse osmosis filtration applications. These types of filters can be periodically backwashed to remove collected contaminants and extend the life of the filter.
Cartridge pre-filters and capsules are primarily used in small to medium-sized systems requiring multiple filtration steps to achieve the desired outcome. They can be installed singly, or in multi-round housings depending on the required flow rate. Some larger systems can use 80-round by 40” long cartridges in a single housing. Systems may employ more than one type of prefilter depending on the particulate and other contaminant content of the fluid being processed, and the required flow rate and batch size.
Activated charcoal filtration can be used to pretreat water for chlorine and other organic chemical contamination. This is especially important in pretreatment for reverse osmosis systems where the membrane is sensitive to chlorine exposure. Depending on system size, the activated charcoal can be used in a larger canister (similar to the sand filter shown above) or can be configured to fit in a standard 3” diameter cartridge size using standard filtration housings.
Bag filters are another common pre-filter configuration. The bag filter is placed in a housing (much like a vacuum cleaner bag) so that fluid flows in the opening and out through the filter material. The bag is then drained and discarded after use.
A simple system may employ a single pre-filtration followed by a final filtration. In this case, the pre-filter is usually some type of depth filter to remove particles, extending the life of the final filter. These filters may be a pleated depth media, a melt-blown filter, or a wound yarn filter, depending on the pore size and removal rating required. Systems can be sized so that both filters will require changing at the same time, or so that the pre-filter can be changed independently.
More complex filtration solutions might require multiple pre-filtration steps. For fluids with high particle loading and a wide range of particle sizes, a higher pore size pre-filter (10+ microns) followed by a pre-filter for finer particles (1 micron or less) followed by the final filter.
In biopharmaceutical applications, this might be a particle filter, a bio-reduction filter, and a sterilizing grade filter. The particle filter prevents fouling of the bio-reduction filter, which in turn removes many of the bacteria that might build up on the sterilizing filter. In cases like this, the particulate filter is often one of the depth filters described above, and the bio-reduction filter is a membrane filter that is not rated for full sterilizing capability.
It is also possible to build in a pre-filter along with a final filter into a single device by layering the appropriate media and membrane(s) during assembly. This is often employed where space limitations may prevent the use of multiple housings.
If you have an application that may benefit from one of our many pre-filtration products, alone or in combination with our membrane filtration products, contact customerservice@criticalprocess.com so we can help you determine the right filters for your application.