Gate valve
Ball valve
Globe Valve
Butterfly valve
Copper valve
Air valve
Pipe Repair & Coupling
Check valve
Ductile iron(DI) pipe fittings
Dismantling Joint
Water Meter

Detailed knowledge of the Strainers(三)

Mechanical type self-cleaning strainers

    Backwashing type strainers reverse the direction of flow through the screen. A set of valves is changed over so that water is directed across the screen in the reverse direction and out through a flush valve. The fluid dislodges any debris entrained in the screen and carries it out in the backwash fluid to a waste drain.
    In addition to the mechanical and backwashing type strainers, there are several types of uniquely designed strainer screens. One of the more common types is the metallic disc, positive edge type strainer (see Figure 12.4.8). The straining element is constructed from a pack of circular discs, separated by spacing washers built on a main shaft with tie rods. The thickness of the washers or distance pieces gives the required degree of filtration. The flow direction of the fluid being strained is from the outside of the element to the hollow core, which is formed by the spaces between the main discs. This means that any debris is trapped on the outside surface of the discs.
    In order to clean the strainer, the entire strainer pack is rotated by the external handle against a set of stationary cleaning knives interleaved with the main pack. During this rotation, accumulated debris builds up on the leading edge of the cleaning knife, and it is deposited into a solid, vertical groove formed in the outside surface of the strainer element by special packing pieces. As there is no flow through this part of the element there is no force holding the accumulated dirt against the element, and it falls into the sump at the bottom of the strainer.