Disk And Screen Filters

Disk filters are a cross between a screen filter and a media filter, with many of the advantages of both. Disk filters are good at removing both particulates, like sand, and organic matter. A disk filter consists of a stack of round disks. The face of each disk is covered with various sized small bumps. A close up view of the bumps reveals that each has a sharp point on the top of it, somewhat like a tiny pyramid.

These bumps are very small, thus a typical disk looks a lot like the old vinyl 45 RPM records! Because of the bumps, the disks have tiny spaces between them when stacked together. The water is forced between the disks, and the particulates are filtered out because they won’t fit through these gaps. The organics are snagged by the sharp points on the bumps. For automatic cleaning of the filter the disks are separated from each other which frees the debris to be flushed out through a flush outlet. For less expensive disk filters you must remove the disks and hose them off.

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 flushing them with a stream of water or removing the screen and cleaning it by hand. 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 outlet. The outlet is opened and it is hoped that the debris washes out of the flush outlet with the water! An improved variation on this is the directed-flow flush. Again a flush outlet is opened, but in this case the structure of the filter is designed so that the flush 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 backflush. The water is forced backwards through the screen by the water pressure in the system, not by a true vacuum.)

So which filter to use? There is no fixed answer. Your budget, water quality, and availability of the filter and parts must all be considered. Screen filters are generally the least expensive. If you have a city water supply with nothing more than a periodic grain of sand or flake of rust in it, a screen filter will be fine in most cases. Sometimes a combination of more than one type of filter will be needed. For a smaller size system a disk filter would remove both sand and organics, but you might need to frequently clean it! Here are some suggestions based on the source of your irrigation water: