Isuzu 4JA1 Workshop Manual page 526

6E-272 Engine Control System (4JH1)
Low Pressure Fuel Circuit Description
Legend
1. Fuel Suction
2. Regulating Valve
3. Overflow Valve
4. Feed Pump
5. To Fuel Tank
The low pressure fuel circuit must supply sufficient fuel
to the high pressure fuel circuit. The main components
are the feed pump, the regulating valve and the
overflow valve.
Feed Pump
Legend
1. Rotor
2. Casing Ring
3. Fuel Supply
4. Outlet
5. Chamber
6. Vane
7. Driveshaft
8. Inlet
9. Fuel Suction
The feed pump is driven by the drive shaft, performs
suction and supply of fuel. The vanes assembled in the
rotor are pressed against the inside of the casing ring
by spring forces and centrifugal force during rotation to
form chambers. When the vanes rotate, the volume of
these chambers increase when they reach recesses the
casing ring connected to the inlet port. Pressure then
decreases and fuel is drawn in. When the chambers
have passed the inlets and recesses, the volume
decreases and the fuel is compressed. Fuel pressure
increases until the chamber reaches the outlet, where
the fuel passes through the regulating valve to the high
pressure fuel circuit.
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Regulating Valve
Legend
1. To Inlet
2. Spring
3. Valve Piston
4. Port
5. From Outlet
When feed pump speed increases so that the delivery
pressure of the fuel delivered from the outlet exceeds
the regulating valve spring force, the plunger is pushed
upwards. Excess fuel passes through the ports and
returns to the inlet side, and the delivery pressure is
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maintained within a specified range. When feed pump
speed decreases so that the delivery pressure
decreases, the plunger is pushed downwards by spring
force to close the port.
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