SERVICE MANUALROBERT BOSCH MODEL MW INJECTION PUMPSection 11because wax particles could plug the filter in coldweather. Fuel lines and fittings between the supplypump inlet and the fuel tank must be a minimum ofthree-eighths inches inside diameter. Small diameterfuel supply lines or fittings will reduce fuel flow and canreduce engine power output.A special hose is used between the primary fuel filteroutlet and the supply pump inlet to dampen supply pumpfuel pulses. Use of a substitute hose in this position cancause lower engine power even though supply pumppressure can be within specifications.Intermediate PressureThe supply pump produces an intermediate pressure,called supply pump pressure at its outlet and forces fuelthrough the final fuel filter and into the injection pumphousing. Fuel under intermediate pressure surroundseach barrel assembly. Fuel pressure in the housing iscontrolled by the orificed fitting in the fuel return hoselocated "downstream" of the fuel return check valve andthe supply pump piston spring calibration. A specialrubber hose between the final filter outlet and theinjection pump housing dampens pressure waves fromthe supply pump. Substitute hoses can cause lowerengine power even though supply pump pressure can bewithin specifications.High PressureThe injection pump meters and delivers fuel at highpressure, up to an instantaneous 9000 psi pressure afternozzle valve opening, through the injection pipes or linesto the injection nozzle assemblies. This high pressurefuel causes the nozzle valve to open and fuel flowsthrough the nozzle orifices into the combustion chamber.The amount of fuel delivered is controlled by the injectionpump governor. A small amount of low pressure fuelreturns from the nozzle assemblies to the fuel tankthrough the leakoff lines.Low PressureAn orifice fitting in the end of fuel hose from the fuelreturn check valve limits the amount of fuel returned tothe fuel tanks. After fuel passes through the orifice, it isat low pressure.SUPPLY PUMP AND HAND PRIMING PUMPCOMPONENTSThe supply pump consists of a pump housing, rollertappet assembly, pressure spindle and "O" ring, plunger,plunger spring, suction valve, pressure valve andassociated fittings, gaskets and covers (Figure 7).Three studs and nuts secure the supply pump andgasket to the injection pump housing. The eccentric onthe injection pump camshaft actuates the supply pumpplunger through the roller tappet and pressure spindle.An "O" ring around the pressure spindle retains the fuelwithin the supply pump. Each injection pump assemblyis equipped with a hand priming pump which is threadedinto the supply pump housing.Figure 7. - Supply Pump and Hand Priming PumpComponentsCGES-185-3PRINTED IN UNITED STATES OF AMERICAPage 6
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