A strainer is a device made of wire mesh screens, which seek to remove large solid particles from a fluid. As part of standard engineering practice, strainers are installed on pipelines ahead of valves, pumps and regulators, in order to protect them from the damaging effects of fluid and other system contaminants.
A common strainer design uses two screens, cylindrical in shape. One cylinder is inside the other and the two are separated by a small space. The outer cylinder is a coarse mesh screen and the inner one is a fine mesh screen. The fluid first passes through the coarse mesh screen and filters the larger particles. It then passes through the fine mesh screen, which blocks the smaller particles. Figure 7.11 shows the cross-sectional view of a typical strainer.
The bottom of the strainer serves as the sump (or pot) for the solids to collect. The strainer can be cleaned out easily at intervals, by two different procedures:
1. The cleanout plug can be removed and the pressure in the line can be used to blow the fixture clean.
2. The large retaining nut at the bottom is to be removed for pulling the mesh out of the strainer in order to clean it and putting it back in line.