In-line self cleaning filter - SS-ILF

To achieve these objectives, the Global FIA design uses two filter elements comprised of 25 µm micro-porous Teflon™ tubing mounted on a probe equipped with 1" flanges for inserting directly into a pipe or tank. During sampling, one of the elements is the inlet to the sampling system while the other is the back-flushing outlet, as shown in the figure below for valve position A.  A Valco four-port (C22‑3184‑EH) valve or two BioChem 3 port solenoid valves provides a means of switching the flow periodically so that the roles of the two elements are exchanged as shown in valve position B. The timing of this switch is dependent on the particle load and nature of solid component in the sample stream Thus, while one filter element is filtering the sample stream, the other is being back-flushed by the filtered stream. A small fraction of the filtered stream (as little as a few µL) is removed to supply the analyzer, making the filter probe ideal for small volume reactors.

Position A                                                                 Position B

Flow through the pump is uni-directional, while flow through the two porous Teflon filter elements is bi-directional, with each filter element spending 50% of the total duty cycle being back-flushed.

Clean sample is removed under analyzer pump suction to the analyzer through a tee.  If desired, this same tee can be used to introduce additional “cleaning fluid” to assist in clearing the pores of the filter element (e.g. an acid solution if the filter cake is calcium carbonate, or a bleach solution if the filter cake is a bio-film, for instance).

Where the filter probe is mounted at right angles to the flow of the process stream, cross flow action will also help to keep the filter elements free of solids build up.

Benefits:

1. Self-cleaning and therefore low maintenance.
2. No wastage of process solution – unused sample is returned to the process.
3. Scaled to deliver the size of sample frequently used in process analyzers.