To remove the element, turn the control valve handle to the BYPASS position. This position will divert the oil flow through the strainer head and will allow you to remove the element without interrupting the oil flow to the engine.

Another type of element consists of a closely compressed coil of stainless steel wire. The wire has been passed between rollers so that it is a wedge-shaped wire or ribbon with one edge thicker than the other. On one side of the wire, projections are spaced at definite intervals. The other side of the wire is smooth. The projections on one side of the wire touch the smooth side of the wire on the adjacent coil to provide ap-propriate spacing between adjacent coils. The

Figure 8-3.-Edge-wound metal ribbon lubrication oil strainer.

thick edge of the wire is on the outside of the coil. A tapered slot is therefore formed from the outside to the inside of the coil, with the narrowest part of the slot on the outside. With this arrangement, dirt particles small enough to pass through the outside, or narrowest, portion of the slot will not become stuck halfway through the slot and clog the oil flow. The dirt removed from the oil remains on the outside of the element and can be readily removed when the element is rotated with the cleaning handle. As the element rotates, the cleaning blade scrapes foreign material from the element.

The control-valve handle on the strainer operates the bypass valve. When the handle is in the ON position, the lubricating oil is flowing through the strainer. When the handle is in the BYPASS position, the oil is flowing directly through the head of the unit, and the strainer case and element can be removed and cleaned. The ON and BY-PASS positions are indicated on the strainer head.

EDGE-DISK STRAINER.-A duplex strainer of the edge-disk type is shown in figure 8-4. The strainer consists of two sections, each of which contains two strainer elements. A control valve between the two sections secures one section while the other remains in operation. The secured section acts as a standby unit; it may be opened for cleaning and inspection without interrupting the straining operation.

A strainer element of the edge-disk type consists of an assembly of thin disks separated slightly by spacer disks. The assembly of an edge-disk strainer element is illustrated in figure 8-5. The lower end of the disk assembly is closed; the upper end is open to the strainer discharge. Oil enters the strainer assembly and is forced down between the casing and disk assembly and then through the disks into the center of the disk assembly. The oil then passes up through the assembly and out through the discharge outlet. In passing through the strainer, the oil passes through the slots between the strainer disks. A relief valve at the bottom of the strainer element relieves pressure which builds up if the slots become filled with foreign matter. The relief valve bypasses the oil up through the center of the strainer element and out through the strainer discharge when a predetermined pressure is reached.

When the assembly is turned by the external handle, the solids which have lodged against or between the disks are carried around until they meet the stationary cleaner blades. The stationary cleaner blades clean the solids from the strainer surface. The solids are compacted by the cleaner blades and fall into the sump of the strainer.

To keep the strainer in a clean, free-filtering condition, give the wing handle on the element that is not in use one or more complete turns in a clockwise direction, then shift the flow to the element you have cleaned. If the handle turns hard, then the strainer surfaces have heavy deposits of solids on them. You must

Figure 8-4.-Edge-disk oil strainer.

then remove the head and disk assembly and soak it in a solvent until the solids are removed.

WIRE-MESH (SCREEN) STRAINER.- Strainers installed on the suction or intake side of the pressure pumps are generally of the wire-mesh (screen) type and are referred to as coarse strainers. Some screen-type strainers are located in the oil pan or sump.