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The choice of ring and grille shall include the following main points:

1. The water quality, the water gate flow, grid position.
2. The grill well depth, width, grid velocity.
3. The installation Angle, height of discharge

According to the inlet water quality, water depth and types of the grille material can be determined. According to the traffic and grid velocity, installation Angle width of grating can be calculated. According to the bars grille location are used to determine the clearance.