PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 2/TASK 2
(c) The cam follower drives the plunger through a spring.
spring is calibrated so that it will flex rather than drive the plunger when
the pressure in the pump chamber reaches the desired maximum.
effectively regulates pump pressure.
d. Gear-Type Supply Pump. The basic overall operation of the gear-type
supply pump is the same as the gear-type oil pump.
All diesel engines require governors to prevent
overspeeding of the engines under light loads.
also demand control of idling speed.
Any of the governors provide a
variable-speed control which, in addition to controlling minimum and maximum
speeds, will maintain any intermediate speed desired by the operator.
Engine speed in a diesel is controlled by the amount of fuel injected. The
injection, therefore, is designed to supply the maximum amount of fuel that
will enable it to operate at full load while reaching a predetermined
maximum speed (rpm). If, however, the maximum fuel charge were supplied to
the cylinders while the engine was operating under a partial or unloaded
condition, the result would be overspeeding and certain engine failure.
Thus, it can be seen that the governor must control the amount of fuel
injected in order to control the engine speed.
Governors may be actuated through the movement of
centrifugal flyweights or by the air-pressure differential produced by a
governor valve and venturi assembly.
The centrifugal flyweight type may incorporate a mechanical linkage system
to control the injection pump, or it may include a hydraulic system to
transmit the action of the weights to the pump. On engines where the rate
of acceleration must be high, the governor-controlling weights must be small
to obtain the required rapid response from the governor.
The problem is
that the smaller flyweights will not exert enough force to control the
injection pump properly. When this is the case, the flyweights will be used
to control a hydraulic relay valve, which, in turn, will control the
injection pump through a servo piston.