Filter location in a hydraulic system is critical to ensuring acceptable levels of fluid cleanliness and adequate component protection. Figure 7.5 shows the location of the various filters in a hydraulic system.
The function of breathers in a hydraulic system is to prevent entry of airborne particles which are drawn into the system due to changes in the fluid level of the reservoir. They are usually mounted on the reservoir. Components such as servo valves which are located immediately downstream of the filter are protected from wear and silting-related problems by pressure filters. These pressure filters are designed to withstand high pump pulsations and the system pressure. Return hne filters provide protection against entry of particulate matter when the fluid is returned to the tank. An off-line filter also known as kidney loop is often provided in a hydraulic system especially when fluid circulation through the return-line filter is minimal. Off-line filters operate on a continuous basis. The chief advantage associated with these filters is the flexibility they offer with regard to their placement. Since these filters are independent of the main system, their location in a hydraulic circuit can be chosen in such a way that easy serviceability is ensured.