SERVICE MANUALROBERT BOSCH MODEL MW INJECTION PUMPSection 11Supply Pump OperationThe supply pump plunger establishes and separates twochambers within the supply pump, the suction chamberand the pressure chamber (Figure 8). Two operatingstrokes occur within the pump operating cycle. Duringthe intermediate stroke, the revolving camshaft eccentricdrives the roller tappet, pressure spindle and pumpplunger towards the plunger spring. A portion of the fuelpresent in the suction chamber equal to the sweptvolume or quantity of fuel or air delivered per strokeflows through the pressure valve to the pressurechamber. Towards the end of the intermediate stroke,the spring loaded pressure valve closes.As soon as the rotating eccentric has reached itsmaximum travel or stroke toward the plunger spring, thedelivery and suction stroke starts. During this stroke, theplunger spring drives the plunger and pressure spindletoward the roller tappet. A portion of the fuel present inthe pressure chamber flows through the pressure valveto the final filter and then to the injection pump housing.Simultaneously during this stroke, fuel flows through thepump suction into the suction chamber.During the spring-actuated delivery and suction stroke,all fuel swept out of the pressure chamber flows out thedischarge fitting. The fuel volume swept out of thepressure chamber is slightly less than the fuel volumeentering the suction chamber. Actual fuel volume sweptout of the pressure chamber is the fuel volume swept outof the suction chamber minus the volume of the pressurespindle reaching into the pressure chamber.Therefore during the intermediate stroke, a quantity offuel corresponding to the volume of the spindle is fed tothe injection pump. For example, if the fuel volume inthe pressure chamber were nine millimeters and the fuelvolume in the suction chamber were ten millimeters at agiven plunger travel, one millimeter would flow throughthe pressure valve during the intermediate stroke.Because the plunger spring provides the force to pumpthe fuel and the camshaft eccentric and roller tappetmerely positions the plunger, supply pump pressure isself-limiting. When supply pump pressure exceeds aspecified value, the plunger spring lifts the plunger onlyINTERMEDIATE STROKEDELIVERY AND SUCTION STROKEFigure 8. - Supply Pump OperationCGES-185-3PRINTED IN UNITED STATES OF AMERICAPage 7
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business
