1. The cartridge-type element (fig. 6-24) fits into a permanent metal container. Oil is pumped under pressure into the container where it passes from the outside of the filter element to the center. From here, the oil exits the container. The element is changed easily by removing the cover from the container.

2. The spin-on filter (fig. 6-24) is completely self- contained, consisting of an integral metal container and filter element. Oil is pumped into the container on the outside of the filter element. The oil then passes through the filter medium to the center of the element where it exits the container. This type of filter is screwed onto its base and is removed by spinning it off.

The elements themselves may be either metallic or nonmetallic. Cotton waste or resin-treated paper is the most popular filter mediums. They are held in place by sandwiching them between two perforated metal sheets. Some heavy-duty applications use layers of metal that are thinly spaced apart. Foreign matter is strained out, as the oil passes between the metal layers.

There are two filter configurations. These are the full-flow system and the bypass system. Operations of each system is as follows:

Figure 6-24. - Oil filters.