The filtering material in the pressure filter, Fig. 4-2, consists of a number of felt discs assembled on a steel tube strainer. This filter may be cleaned by repeatedly dipping the felts into fuel oil or kerosene, holding hand over bottom of stack and blowing dry compressed air from the inside until the felt appears to be clean. The fuel injection pumps, Fig. The high pressure is built up by a constant stroke pump plunger.
Oil flows from the low pressure header into a sump in the upper part of the pump housing.
As soon as the upper edge of the plunger, during its downward stroke, opens the two radial opposite ports in the barrel known as the inlet and by-pass ports, the fuel flows into the barrel while the plunger is at the bottom of its stroke. During the first part of the upward stroke of the plunger some of the fuel in the barrel is forced back into the sump through the inlet and by-pass ports until these ports are closed by the double helix cut in the plunger. The plunger then builds up high pressure within the barrel unseats the delivery valve and forces oil through the high pressure pipe to the injection nozzle. The amount of fuel delivered to the nozzle depend upon the lift required for the helix to open the by-pan port. This is controlled by the fuel pump rack which moves in and out, turning the plunger through a control sleeve so as to give an earlier or later port opening.