Coolant Filter Requires No Replaceable Elements

These coolant filters require no replaceable filter elements. When they become loaded with trapped particles, back flushing restores them to like-new condition.

Top: In the filtering mode, the filter plates and wave washers are compressed, creating gaps that trap particles as small as 5 microns. Bottom: When the filter element is decompressed, the wave washers spring back to their original shape, widening the gaps and permitting trapped particles to be washed away by back flushing.

The filtration system, which provides completely automatic back flushing, consists of the filter unit (left), a reservoir that holds the fluid required for back flushing (upper right) and the tank for collecting particles flushed from the filter.

The Series FN1 filter for machining fluids from SMC Corporation of America (Indianapolis, Indiana) is designed without throwaway filter elements. Instead, it back flushes the trapped particles away from the permanent filtering element to restore its effectiveness. The operating principle is similar to a backyard swimming pool.

The unit's filter element is constructed of a series of grooved filter plates and wave washers (see diagram) placed one above the other and compressed by a compact cylinder fitted on top of the filter housing (see photo). When the element is compressed, foreign matter in the fluid is trapped between the plates and washers. Decompressing the element allows the trapped particles to be back flushed and washed away for collection, eliminating the need for element replacement and providing a low-maintenance operating regime. Once the filter element is back flushed, it is recompressed and filtering resumes.

The filter element is available in cylindrical and step-type versions. In the cylindrical type, the filter plates and wave washers have the same diameter, making for a cylindrical filter element with a periphery that is smooth and regular. The cylindrical element is designed for filtering particles of approximately the same size. It provides a large filtration area and relatively easy particle separation. In the step-type filter element, the diameter of the wave washers is larger than that of the filter plates, making for a filter element that is periphery grooved or “stepped” at regular intervals. The step-type filter is recommended for processing fluids containing particles that are less uniform in size.

The filter is available with 250-mm or 500-mm element lengths, offering flow rates of 40 and 80 liters per minute respectively at 20-micron filtration. (The filter is also available with 5-micron filtration.) For larger flow rates, SMC offers a 200-liters-per-minute filter because a special or standard filter can be mounted in parallel. In installations involving multiple standard units, circuits can be established that permit clogged units to be back flushed, while adjacent units continue to filter.

The FN1 filter not only eliminates the cost of disposable filter elements, but also the cost of replacing them. SMC also notes that the filter can help firms achieve their goal of becoming environmentally friendly enough to meet the ISO 14001 standard.