ROBERT BOSCH MODEL MW INJECTION PUMP
because wax particles could plug the filter in cold
weather. Fuel lines and fittings between the supply
pump inlet and the fuel tank must be a minimum of
three-eighths inches inside diameter. Small diameter
fuel supply lines or fittings will reduce fuel flow and can
reduce engine power output.
A special hose is used between the primary fuel filter
outlet and the supply pump inlet to dampen supply pump
fuel pulses. Use of a substitute hose in this position can
cause lower engine power even though supply pump
pressure can be within specifications.
The supply pump produces an intermediate pressure,
called supply pump pressure at its outlet and forces fuel
through the final fuel filter and into the injection pump
housing. Fuel under intermediate pressure surrounds
each barrel assembly. Fuel pressure in the housing is
controlled by the orificed fitting in the fuel return hose
located "downstream" of the fuel return check valve and
the supply pump piston spring calibration. A special
rubber hose between the final filter outlet and the
injection pump housing dampens pressure waves from
the supply pump. Substitute hoses can cause lower
engine power even though supply pump pressure can be
The injection pump meters and delivers fuel at high
pressure, up to an instantaneous 9000 psi pressure after
nozzle valve opening, through the injection pipes or lines
to the injection nozzle assemblies. This high pressure
fuel causes the nozzle valve to open and fuel flows
through the nozzle orifices into the combustion chamber.
The amount of fuel delivered is controlled by the injection
pump governor. A small amount of low pressure fuel
returns from the nozzle assemblies to the fuel tank
through the leakoff lines.
An orifice fitting in the end of fuel hose from the fuel
return check valve limits the amount of fuel returned to
the fuel tanks. After fuel passes through the orifice, it is
at low pressure.
The supply pump consists of a pump housing, roller
tappet assembly, pressure spindle and "O" ring, plunger,
plunger spring, suction valve, pressure valve and
associated fittings, gaskets and covers (Figure 7).
Three studs and nuts secure the supply pump and
gasket to the injection pump housing. The eccentric on
the injection pump camshaft actuates the supply pump
plunger through the roller tappet and pressure spindle.
An "O" ring around the pressure spindle retains the fuel
within the supply pump. Each injection pump assembly
is equipped with a hand priming pump which is threaded
into the supply pump housing.
Figure 7. - Supply Pump and Hand Priming Pump
PRINTED IN UNITED STATES OF AMERICA