There are two types of screens used in strainers:
Perforated Screen
These are formed by punching a large number of holes in a flat sheet of the required material using a multiple punch. The perforated sheet is then rolled into a tube and spot welded together. These are relatively coarse screens and hole sizes typically range from 0.8 mm to 3.2 mm. Consequently, perforated screens are only suitable for removing general pipe debris.
Mesh Screen
Fine wire is formed into a grid or mesh arrangement. This is then commonly layered over a perforated screen, which acts as a support cage for the mesh. By using a mesh screen, it is possible to produce much smaller hole sizes than with perforated screens. Hole sizes as small as 0.07 mm are achievable. Subsequently, they are used to remove smaller particles which would otherwise pass through a perforated screen. Mesh screens are usually specified in terms of ‘mesh’; which represents the number of openings per linear inch of screen, measured from the centre line of the wire.
