Oil filter

An oil filter assembly for a machine that provides an oil output port and an oil input port, the oil filter assembly comprising:

• a mounting plate fixed with an outer enclosure, the mounting plate adapted for securing to the machine, for conducting oil from the oil output port of the machine into a peripheral portion of the outer enclosure, and for returning oil from a central portion of the outer enclosure into the oil input port of the machine;
• a primary filter having a first porosity and through which oil may pass to move from the peripheral portion to the central portion of the outer enclosure;
• a pressure-actuated valve fixed fluidly between the peripheral and central portions of the outer enclosure and through which oil may pass only when an oil pressure differential between the peripheral portion and the central portion of the outer enclosure exceeds a predetermined threshold;
• and
• a secondary filter having a second porosity greater than the first porosity and fixed fluidly between the pressure-actuated valve and the central portion of the outer enclosure;
• whereby oil traversing through the oil filter assembly must pass through either the primary filter, or, if the predetermined pressure threshold has been reached, either the primary or the secondary filter, and
• wherein the primary filter is substantially cylindrical and includes an end cap with a threaded aperture for mounting thereto a secondary filter assembly that includes a secondary filter housing that at least partially encloses the secondary filter and fixes the secondary filter and the pressure-actuated valve to the end cap with a ball seat and seal plate.