PRINCIPLES GASOLINE/DIESEL FUEL SYSTEMS - OD1620 - LESSON 1/TASK 2
FIGURE 4. MECHANICAL NONPOSITIVE
TYPE FUEL PUMP.
(7) Pressure will build in the fuel line and the pump chamber as the
fuel pump fills the carburetor bowl. As the pressure rises to the desired
level in the pump chamber, it will hold the diaphragm down against the
pressure of the diaphragm spring. The rocker arm will move up and down in
the slotted pull rod. There will be no pumping action until the fuel line
pressure again drops below the desired level. In this way, the nonpositive
type fuel pump regulates fuel line pressure. Normal pressure range is from
1.5 to 6 pounds per square inch (psi). The operating range of the pump
depends on the tension exerted by the diaphragm spring.
(8) A venthole is provided under the diaphragm to allow the pressure
to change in the lower chamber as the diaphragm flexes.
(9) The pulsation chamber, located above the pump chamber, uses a
soft diaphragm and a sealed