People often discuss the different methods for defining the performance of their filter cartridge e.g.  beta ratios, percentage,  efficiencies, titre reductions, diffusion flow values etc. All of these have great merit as it is important to understand how the filter you have chosen to use will affect your process.

 DOE and SOE cartridges

 DOE and SOE Design Cartridges (DOE at front)

Whilst most filter companies strive to provide their clients with the best performing cartridge and provide the data to back it up, often the importance of the sealing mechanism on the cartridge can be over looked. There are two common types of cartridge sealing mechanisms used on most filters, Double Open End (DOE) and Single Open End (SOE).

The more simple, low cost DOE design often has a basic polypropylene core and flat gaskets either end. The cartridge is sealed into the housing using a knife edge sealing mechanism.

This design is adequate for systems where high removal efficiencies or fine filtration are not required. In addition they are not suited to applications that see significant temperature changes as different levels and rates of expansion of the metal and plastic components in the filter system mean that the cartridge to housing seal could be compromised and allow by-pass of contaminants.

The SOE cartridge design involves a plug in adaptor typically fitted with two o rings. This provides a positive seal that is unlikely to be compromised by varying process conditions or poor fitment. This provides a minimal risk option.

Therefore DOE cartridges tend to be associated with nominal rated, low efficiency filters or as pre filters at less critical parts of the process. These are ideal in these applications and offer the most economical solution. SOE cartridge design tends to be used with absolute rated filters where maximum performance is expected from the filter, such as a final trap, polishing or sterilising applications.

Which Cartridge Design Is Best For Critical Applications?

However, we still find many applications in the market where people select high performance filters, but choose the DOE design of cartridge and use these in low performance housings and then suffer the ongoing problems associated with that.

Filtrate bypassing is then possible due to a variety of reasons such as poor length (too long, too short), damaged knife edge seals on the filter vessel, an over eager operator who over compresses the filter and very often on small single cartridge housings, where the operator has to ‘guess’ that the filter has indeed sealed at all.

Therefore cartridge design selection is crucial and a full understanding of the process and criticality is required in order to adopt the right solution.  A cartridge may be developed as a high performance filter, but all the 99.99% removal efficiency could be wasted if the seal is not right !

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This entry was posted on 30th Apr 2015