There are three general areas in a system for locating a filter: the inlet line, the pressure line, or a return line. Both filters and strainers are available for inlet lines. Filters are normally used in other lines.

Inlet Filters and Strainers

Figure 9-40 shows the location of an inlet line filter. An inlet line filter is usually a relatively coarse mesh filter. A fine mesh filter (unless it is very large) creates more pressure drop than can be tolerated in an inlet line.

Figure 9-41 shows a typical strainer of the type installed on pump inlet lines inside a reservoir. It is relatively coarse as filters go, being constructed of fine mesh wire. A 100-mesh strainer protects the pump from particles about 150 microns in size.

Pressure Line Filters

A number of filters are designed for installation right in the pressure line (fig 9-42) and can trap much smaller particles than inlet line

Figure 9-42.-Pressure line filter.

Figure 9-43.-Return line filter.

filters. Such a filter might be used where system components, such as valves, are less dirt-tolerant than the pump. The filter thus would trap this fine contamination from the fluid as it leaves the pump. Pressure line filters must be able to withstand the operating pressure of the system.

Return Line Filters

Return line filters fig 9-43 also can trap very small particles before the fluid returns to the reservoir/tank. They are particularly useful in systems that do not have large reservoirs/tanks to allow contaminants to settle out of the fluid. A return line filter is nearly a must in a system with a high-performance pump, which has very close clearances and usually cannot be sufficiently protected by an inlet line filter.