Screen is composed of a set of parallel metal grids. the main application industries are water treatment, wastewater treatment, oil, and gas, power generation, food and beverage, mining, pharmaceutical, pulp, and paper, etc; which are generally placed obliquely in front of the sewage lift pump collection tank or on the water inlet channel to intercept large solid objects that are suspended or floating in the water (such as grass, wood, plastic Products, fibers, and other domestic garbage, etc.) to prevent clogging or damage to valves, pipes, pumps or other subsequent processing equipment. The screen can be divided into two types: manual screen and mechanical screen. Manual screens are mostly used in small water treatment processes; mechanical screens are mostly used in large water treatment processes. The mechanical screen has a complex structure and a large amount of maintenance, but the degree of automation is high. Compared with the manual screen, it can reduce the labor intensity of the staff.
Pay attention to the following points when selecting samples and installing screen:
1. The screen grid spacing should meet the requirements of the pump structure (usually the grid spacing is smaller than the minimum gap of the pump impeller) and the flow requirements of the subsequent water treatment equipment (Table 5-0-1).
When the coarse and fine screens are not divided, a smaller grid spacing can be selected.
2. There are many kinds of cross-section shapes of commonly used lattice grids, and rectangular cross-sections are mostly used. Although circular grids have good hydraulic conditions and low flow resistance, they have poor rigidity and are easily deformed by external forces.
3. The screen is generally installed at the head of the treatment process or at the water inlet of the pumping station, so there must be a backup water source channel, or appropriate measures must be taken to overhaul the screen without stopping the water.
4. The channel in front of the screen should have a straight pipe section of more than 5m, with a flow rate of 0.4-0.9m/s to ensure that the flow rate through the grid is 0.6~1.0m/s
5. Consider using manual cleaning, so the installation angle of the screen should be 45°~60°, not too large.
6. When the sewage contains volatile combustible gases, the power device of the mechanical screen should have explosion-proof facilities.
7. When the screen is equipped with a grid-top working platform, its height should be more than 0.5m higher than the highest design water level in front of the grid, and the working platform should have safety facilities such as railings and washing facilities; the platform aisles on both sides should be no less than 0.7m, and the width of the front aisle Should not be less than 1.5m
2. Technical parameters: The main technical parameters of the manual screen are shown in Table 5-1-1 and Table 5-1-2
3. Equipment specifications: The specifications of the bar screen are shown in Table 5-1-1. The specifications of the mesh screen are shown in Table 5-1-2.
4. Pay attention to the following points when installing screen:
(1) Materials that should be available during installation:
①Design drawings: including general drawings, assembly drawings, hydraulic building drawings, and installation control point location drawings. ②Technical documents: including screen manufacturing acceptance data (including material list), certificate of conformity.
(2) When installing the screen, it must be carried out according to the design drawings.
(3) The measuring tools used to install the screen must meet the specified requirements and be verified by the statutory metrology department.
(4) Welding materials must have ex-factory quality certificates, and their various indicators shall comply with relevant standards.
(5) The appearance quality requirements and internal defect detection of welds shall meet the requirements of SL 36-92 “General Technical Conditions for Welding of Hydraulic Metal Structures”. The allowable deviation of screen positioning during installation should meet the requirements of Table 5-1-3.