PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 2/TASK 2
The chamber on one side of the diaphragm is open to atmosphere, and on the
other side it is sealed and connected to the venturi in the manifold. In
addition, there is a spring acting on the sealed side of the chamber, which
moves the diaphragm and the control rod to the full-fuel position normally.
(2) When the engine is running, the pressure in the sealed chamber is
reduced below the atmospheric pressure existing in the other chamber. The
amount of pressure reduction depends on the position of the governor valve
and speed of the engine.
It is this pressure differential that positions
the diaphragm and, consequently, the control rod of the injection pump. The
governor valve is controlled by a lever that is connected by suitable
linkage to the foot throttle. There is no mechanical connection between the
foot throttle and the control rod of the injection pump.
(3) If the engine is operating under load and the speed (rpm) is
below governed speed, the velocity of air passing through the venturi is
comparatively low and only a slight pressure differential is present. This
will cause the spring to move the diaphragm and the injector pump