F-F-351F
3.4.1.2.1.3 Cover screw gasket. The cover screw gasket shall seal the joint between
cover hole and cover screw gasket seat. Construction shall be of permanent type, with material
optional. Dimensions shall conform to F-F-351/2.
3.4.1.2.1.4 Cover gasket. The cover gasket shall seal the joint between the cover flange
and the body. For type I, class 3 filter, cover gasket shall conform to F-F-351/6.
3.4.1.2.1.5 Element hold-down spring. When in place on cover, cover screw shall carry a
cylindrical or conical spring, so secured that it may be removed from the screw for servicing cover
screw gasket. The spring force shall be not less than 15 nor more than 35 pounds (lb) (not less than
6.8 nor more than 16 kilograms (kg)) (see 4.6.9).
3.4.1.3 Center tube.
3.4.1.3.1 Class 3. For class 3 filters, the center tube shall be constructed of seamless steel
tubing or of a material with equivalent characteristics, with adequate wall thickness to provide
tensile strength sufficient to operate safely with an applied tightening torque of 25 ft-lb. The tube
shall be free of burrs and shall contain a stop or collar to position and support the lower end of the
filter element. The tube shall be provided with an orifice drilled through one side of the wall of the
center tube to serve as an outlet passage for filtered oil. It shall conform dimensionally to F-F-
351/2.
3.4.1.4 Base. For class 3, base-mounted filters, the base shall conform to F-F-351/2.
Design and arrangement of inlet and outlet passages are at the manufacturer's option. A check
valve, for the prevention of oil drainback, shall be provided and shall conform to the dimensional
limitations as specified in F-F-351/2. Otherwise, design and method of check valve installation is
optional. A drain passage shall be provided to facilitate element replacement and shall have a plug
not smaller than 0.25 in. (6.4 millimeters (mm)) NPTF, dry seal.
3.4.1.5 Antidrain-back seal. Type I bypass flow filters with integral elements shall be
provided with an antidrain-back seal (valve).
3.4.1.6 Installation arrangements.
3.4.1.6.1 Class 1. As specified (see 6.2), straps, brackets or other means for installation
on or near the engine to be served shall be incorporated into the design of the type I, class 1,
style B filter. Unless otherwise specified (see 6.2), oil lines and oil line fittings shall not be
required as part of the complete filter assembly.
3.4.1.6.2 Class 3. Class 3 filters shall be arranged for base-mounted installation in
accordance with F-F-351/2.
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