In filters approved by the Navy, the absorbent material is composed of such substances as cellulose, cotton yarn, and paper disks. Filters may be located directly in the pressure-lubricating oil system, or they may be installed as bypass filters. When installed in the pressure system, a filter must contain a built-in, spring-loaded, pressure-relief valve. The valve must be large enough to bypass all oil to the engine in case the filter element becomes restricted.

A bypass filter has an orifice plate in the line to the filter. This component controls the amount of oil removed from the lubricating oil pressure system. (The amount of oil that flows through a bypass filter is only a small percentage of the oil that flows through the pressure system.) The oil from a bypass filter is returned to the sump tank. Filters vary as much in design and construc-tion as do strainers. Examples of some of the filters with which you will come into contact are shown in figures 8-6 and 8-8.

TANK-TYPE FILTER.-Figure 8-6 illus-trates the basic design of a tank-type filter. A tank-type filter consists of a single tank that holds

Figure 8-5.-Edge-disk strainer element assembly.

Figure 8-6.-Tank-type lubricating oil filter.

several filter elements. In some tank-type filters, each filter element holder has a relief valve to pro-tect the element against excessive pressure. Other tank-type filters are constructed to withstand pres-sure greater than that of the relief valve setting on any of the pumps in the lubricating oil filtering system.

SPIN-ON FILTER. -The spin-on filter is not unlike the filter you would find on an automobile engine. The spin-on filter consists of a shell, an element, and a gasket combined into a unitized assembly. An oil filter adapter that contains a bypass valve assembly provides the support for each pair of oil filters.

CANISTER-TYPE FILTER.-The canister-type filter assembly consists of a replaceable element enclosed within a shell which is mounted in an adapter or base. When the filter shell is in place, the element is restrained from movement by a coil spring. The bypass valve assembly contained in the adapters will be explained in the next section of this chapter.

Up to this point in the chapter, we have discussed only the main components of an engine lubricating system. You should also be familiar with the piping and gauges, thermometers, and other instruments essential for safe, reliable operation of the system. In the remainder of this chapter, we will deal with the types of lubricating oil filtering systems, the flow of oil through a lubricating oil filtering system (including the internal or engine part of the system), how and why lubricating oil systems are ventilated, and the requirements for testing.