The in-line, self-cleaning filter probe provides a means of filtering sample while simultaneously clearing solids from the filter. This is achieved by having two parallel filters where one filter is filtering sample and the other is being back flushed. The filter probe can be installed directly in a process pipe or tank, or equally well in a bypass stream. The design incorporates several innovations aimed at providing a simple, robust, low-maintenance sampling system.These innovations achieve three main objectives:

Make the probe easy to install in a process pipe or tank.

• Keep the filter elements clean automatically without having to change filters.
• Minimize the filtered fluid volume removed to supply analyzer to µL per analytical cycle, without introducing excessive lag time.

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 for Pos A. A Valco four-port (C22‑3184‑EH) valve or two BioChem 3 port solenoid valves provide a means of switching the flow periodically so that the roles of the two elements are exchanged as shown in for Pos B. The timing of this switch is dependent on the particle load and nature of the 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 back into the process. 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.

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.

The clean sample is removed by the analyzer through a tee. If desired, this same tee can be used for the introduction of 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 buildup.

Benefits:

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