PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 2/TASK 2
(b) The pump plunger has a spoonlike recess in its diameter about
halfway down its sides which, in conjunction with the pump cylinder, forms
the distribution chamber. A slot is cut into the plunger at the top of the
As it reciprocates, the plunger is also rotated
through a quill gear. As it rotates, the slot lines up with equally spaced
passages around the inside of the plunger bore. Each passage is connected
to a fuel injector. The reciprocating and rotating motion are timed so that
the plunger will go through a delivery stroke as the slot lines up with each
This enables the PSB injector pump to deliver a fuel
charge to each consecutive injector every time the plunger makes one
(c) The PSB pump is geared to the engine so that the camshaft
rotates at crankshaft speed.
The cam contains half as many lobes as the
engine has cylinders (there would be three cam lobes if the engine had six
The pump plunger is geared to rotate at one-half of camshaft
speed. This arrangement allows the PSB pump to deliver a charge of fuel to
each injector for every two crankshaft revolutions corresponding to the
requirements of a four-stroke cycle diesel.
(d) A hole, called a spill port, is drilled through the lower
portion of the pump plunger.
The spill port is connected to the pump
chamber by another drilled passage. The spill port is covered by a plunger
sleeve whose position is adjusted by the control lever through an
eccentrically mounted pin.
(e) The movement of the control lever controls the up and down
position of the plunger sleeve.
The position of the control lever is
determined by the governor.
When the sleeve is in its extreme downward
position, the spill port is immediately uncovered as the plunger begins its
delivery stroke. This causes all of the pressure from the pump chamber to
bleed off to the pump return.
In this position, there will be no fuel
delivery to the injectors.
(f) When the plunger sleeve is in the extreme upward position, the
spill port is covered until the plunger almost reaches the end of the
delivery stroke. This position will deliver maximum fuel to the injectors.
As the plunger moves upward, the