Screen filters (3/4", 1", 1 1/2" and 2" with 40 to 200 mesh):
Screen filters are probably the most common filters and in most cases the least expensive. Screen filters are excellent for removing hard particulates from water, such as sand. They are not so great at removing organic materials such as algae, mold, slime, and other unmentionables! These non-solid materials tend to embed themselves into the screen material where they are very difficult to remove. In other cases they simply slide through the holes in the screen by temporarily deforming their shape.
Screen filters are cleaned by removing the screen and cleaning it by hand, or thru automatic flushing using the system water. Depending on the flush method used you will probably have to periodically hand clean the screen to remove garbage not removed by flushing.
Several methods of flushing are common. The simplest is a flush valve outlet. The valve outlet is opened and it is hoped that the debris washes thru the flush valve outlet! An improved variation on this is the directed-flow flush valve. Again a flush valve outlet is opened, but in this case the structure of the filter is designed so that the flush valve flow rushes over the face of the screen sweeping the debris along with it (Somewhat like hosing off a sidewalk with a strong stream of water). This is the most common method found in inexpensive filters.
The most effective method of flushing is the backwash method, but these filters are typically more expensive. In this method the flush water is forced backwards through the screen for a very effective cleaning. This is accomplished by either using two filters side-by-side (the clean water from one is used to flush the other) or by "vacuuming" the screen with a small nozzle, which is moved over the screen by a mechanism in the filter, "sucking" the debris off of it. (Although it is referred to as vacuuming it is really a form of back flush. The water is forced backwards through the screen by the water pressure in the system, not by a true vacuum.)
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