יום חמישי, 30 ביולי 2009

Screen filters, Filtration methods common in irrigation systems, 2


Screen Filters are probably the oldest and most common in irrigation systems. They are excellent in their ability to remove hard particles like rust. But when it comes to sand, it can get stuck inside the screen and rapidly block it. Usually Screen Filters are less expensive. Delicate organic materials cross the screens and raw material usually smears on top of the screens, deriving a more frequent cleaning interval. The common solution in Screen Filters is enlarging the filtration to expand the cleaning intervals. Today, there are several modern solutions of self-cleaning Screen Filters. This is done by back-washing and / or repeat wash using a sprinkler with inner spraying nozzles for cleaning (similar methods used in commercial dish-washers machines). In order to wash the filter in clean water, it takes at least 2 parallel filters, so that one contributes clean water to wash the other. Semi automatic screen filters are available as well, when the filter is being washed by turning a manual crank that rotate internal nozzles spine or a circular brush. If there is no automatic self-cleaning mechanism, the use of Screen Filters is not recommended in case the water contains organic materials. Clogging of material on top of the screens causes a large pressure difference that can bring to the collapse of the screen, or decreasing and even full stopping of irrigation water flow. The Screen Filter is cleaned by removing the screen and washing it under Strong flow of water or by using a suitable brush. The common irrigation screen filtration elements in the market are usually made of Stainless Steel, Polypropylene or Nylon. for drip irrigation use a 120 mesh to 140 mesh screens.
Jack Z.

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