HEATING AND VENTILATION (Description): DESCRIPTION AND OPERATION (page 7 of 10)

HEATING AND VENTILATION

DESCRIPTION AND OPERATION

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FBH fuel pump
The FBH fuel pump regulates the fuel supply to the FBH unit. The FBH fuel pump is installed in a rubber mounting on 
the chassis crossmember immediately in front of the fuel tank. The pump is a self priming, solenoid operated plunger 
pump, with a fixed displacement of 0.063 ml/Hz. The ECU in the FBH unit outputs a pulse width modulated signal to 
control the operation of the pump. When the pump is de-energised, it provides a positive shut-off of the fuel supply to 
the FBH unit.

FBH fuel pump nominal operating speeds/outputs

Sectioned view of FBH fuel pump

1 Solenoid coil
2 Plunger
3 Filter insert
4 Fuel line connector
5 'O' ring seal

6 Spring
7 Piston
8 Bush
9 Fuel line connector

10 Non return valve

The solenoid coil of the FBH fuel pump is installed around a housing which contains a plunger and piston. The piston 
locates in a bush, and a spring is installed on the piston between the bush and the plunger. A filter insert and a fuel 
line connector are installed in the inlet end of the housing. A non return valve and a fuel line connector are installed 
in the fuel outlet end of the housing.

While the solenoid coil is de-energised, the spring holds the piston and plunger in the 'closed' position at the inlet end 
of the housing. An 'O' ring seal on the plunger provides a fuel tight seal between the plunger and the filter insert, 
preventing any flow through the pump. When the solenoid coil is energised, the piston and plunger move towards the 
outlet end of the housing, until the plunger contacts the bush, and draw fuel in through the inlet connection and filter. 
The initial movement of the piston also closes transverse drillings in the bush and isolates the pumping chamber at 
the outlet end of the housing. Subsequent movement of the piston then forces fuel from the pumping chamber through 
the non return valve and into the line to the FBH unit. When the solenoid coil de-energises, the spring moves the piston 
and plunger back towards the closed position. As the piston and plunger move towards the closed position, fuel flows 
passed the plunger and through the annular gaps and transverse holes in the bush to replenish the pumping chamber.

Operating phase

Speed, Hz

Output, l/h (US galls/h)

Start sequence

0.70

0.159 (0.042)

Part load

1.35

0.306 (0.081)

Full load

2.70

0.612 (0.163)