TUBE 3157685 - Caterpillar

Illustration 1 g03782843Fuel should flow from the pick-up in the tank into the in-line filter ( 0.070 mm (0.00276 inch) screen). The clear plastic in-line filter will have air in the top of the filter. Refer to Illustration 1.Note: As the in-line filter accumulates debris, there will be less and less air in the filter.The lift pump should be providing 82 kPa (12 psi) dead headed, and a 1.89 L (0.5 US gal) per minute flow rate (free flow). Fuel then flows out of the lift pump into the fuel filter. The visible fuel in the filter is the dirty unfiltered fuel. The fuel flows inwards through the filter element towards the center of the filter.
Illustration 2 g03782846There is a check valve (1) in the fuel filter base. There is an orifice in the check valve to purge the air. The orifice is on the dirty side of the fuel filter because the filter will not allow air to go through when the filter is wet. If the filter has air present, check for blockage at the check valve. The in-line filter will capture any debris that could plug the orifice.Clean fuel comes through location (2) through 1-2 psi check valve (3) to the high-pressure pump. Check valve (3) must be in place to reduce pressure from the lift pump. The high-pressure pump cannot take full system pressure from the lift pump.