The droplets formed by the coalescing action can be removed from the main stream by using purely gravity or by employing separator cartridges. The majority of the droplets formed will settle within a short period of time. Smaller droplets will require a longer retention time to be separated from the main flow. In applications where due to the process conditions the reliability of separator cartridges is questionable the use of gravity separation is preferred. In other applications the benefit of smaller vessels is appreciated resulting in vessels which combine coalescer and separator cartridges.
Vessels usually contain more than one of each element type. Each element has a maximum recommended flow rate. This may dependent on the application. The length of these elements can vary up to 1420 mm or 56″. The filter water separator can be orientated either vertically or horizontally.
Mechanism of separation
Inconsistencies can be caused by excessive additive content, certain chemical impurities or microbiological growths in the hydrocarbon, and through combinations of these possibilities there is a likelihood that some of the water droplets emitted by the coalescer cartridge will be too small to fall to the sump within the short available distance within the vessel. To prevent the carry-over of these smaller droplets into the filter/separator outlet a bank of stripper cartridges is interposed between coalescer cartridges and the outlet to act as a safety screen. This screen is, in reality, a hydrophobic (water-repellent) barrier, which allows the passage of fuel but prevents the penetration of water. The stripping mechanism is illustrated above and is known as ‘pore catchment’. By combining water resistance and a critical pore or mesh size the media repels any suspended water droplets and, while they are held against the surface of the media by the flow trying to force them through the holes, further droplets following behind will collide and merge with the initial droplets until they are enlarged to such a size that they will fall, under gravity, to the sump area below.
The stripper cartridges are, like the coalescer cartridges, cylindrical in shape but the media is a cylindrical wrap (horizontal and vertical units) or pleated element (vertical units only) of special material. The optional materials available are a high strength siliconised paper, Teflon-coated fine mesh, or a unique woven synthetic material. Stripper cartridges in the latter material simply require thorough cleaning at each service period.
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