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Mechanical filters - Stationary screens
Unit 12 - Management of ponds
Filtration
Classification according to form of materials
Mechanical filters
Stationary screens
Screens are probably the most widely known mechanical filters. The simplest form consists of a stationary screen placed across the fluid flow path such that the fluid must pass through it. Particles larger than the screen mesh cannot pass through the screen and are collected on it. Stationary screens are rarely used for particles smaller than 1.5 mm in diameter or in circumstances of high particle concentration. Rigid plugging occurs if the concentration of suspended particles is too high. Cleaning consists of removing the screen from its operating position and back washing it. (i.e. forcing water though the screen in the reverse direction) with high pressure water or mechanically cleaning it by hand, brush or other means.
Stationary screens are in expensive, easy to install and operate and capable of removing particles larger than the screen mesh. If the fluid contains a high concentration of suspended materials, however screens cleaning labour costs are high. If not properly cleaned, the screens seriously impede flow. Screen mesh sizes are available from several centimetres to few microns. Screen cost rises rapidly as mesh size is reduced below 1.5 to 3 mm. Screens are available in variety of materials such as carbon, steel, brass, stainless steel and cloth fabrics of various types. Plastics are available for use in corrosive fluid, but these require special attention in design because of their low strength characteristics.
Screens are probably the most widely known mechanical filters. The simplest form consists of a stationary screen placed across the fluid flow path such that the fluid must pass through it. Particles larger than the screen mesh cannot pass through the screen and are collected on it. Stationary screens are rarely used for particles smaller than 1.5 mm in diameter or in circumstances of high particle concentration. Rigid plugging occurs if the concentration of suspended particles is too high. Cleaning consists of removing the screen from its operating position and back washing it. (i.e. forcing water though the screen in the reverse direction) with high pressure water or mechanically cleaning it by hand, brush or other means.
Stationary screens are in expensive, easy to install and operate and capable of removing particles larger than the screen mesh. If the fluid contains a high concentration of suspended materials, however screens cleaning labour costs are high. If not properly cleaned, the screens seriously impede flow. Screen mesh sizes are available from several centimetres to few microns. Screen cost rises rapidly as mesh size is reduced below 1.5 to 3 mm. Screens are available in variety of materials such as carbon, steel, brass, stainless steel and cloth fabrics of various types. Plastics are available for use in corrosive fluid, but these require special attention in design because of their low strength characteristics.
Last modified: Thursday, 28 April 2011, 5:47 AM