Fuel Pump: Description and Operation
Modular Fuel Sender Assembly
The modular fuel sender assembly consists of the following major components: a fuel sender cover assembly, fuel pipes (above cover), a fuel pump, a fuel pump strainer, a fuel pump reservoir, an external fuel sender strainer, a ceramic card fuel level sensor assembly, and a fuel tank pressure sensor.
The fuel level sensor assembly consists of the float, the wire float arm, and the rheostat. The fuel level is sensed by the position of the float and float arm, which operates the rheostat. As the float position changes, the amount of current passing through the rheostat varies, thus changing the Gauge reading on the instrument panel.
The modular fuel sender assembly mounts to the opening of the plastic fuel tank. The spring loaded reservoir. The design provides:
- Optimum fuel level in the integral fuel reservoir during all fuel tank levels and driving conditions.
- Improved tank fuel level measuring accuracy.
- Improved coarse straining and added pump inlet filtering.
- More extensive internal fuel pump isolation for noiseless operation.
Modular Fuel Sender Assembly Fuel Flow
The modular fuel sender assembly maintains optimum fuel level in the reservoir (bucket). Fuel entering the reservoir (bucket) is drawn in by:
- The first stage of fuel flow is through the external strainer. And/Or
- The umbrella valve, Or
- The return fuel pipe, whenever the level of fuel is below the top of the reservoir.
The fuel pump used in this system is part of the fuel sender assembly. The fuel pump lower connector assembly prevents the transmission of vibration and noise generated by the pump to the fuel tank.
Fuel enters the lower inlet port (secondary umbrella valve located inside of lower inlet port) of the fuel pump after being filtered by the external fuel strainer, and the fuel pump strainer. The initial function of the pump is to fill the reservoir.
The second stage separates vapor from the fuel in the pump. This vapor separation maximizes hot fuel handling and permits the vapor to return to the fuel tank at lower pressure and temperature. By creating positive fuel pressure, the pump then discharges the liquid fuel into the third stage of the pump. The pump outlet allows the fuel volume to flow through a check valve into the fuel pump flex pipe. The check valve seat is molded inside the connector body. The check valve body and retainer are assembled into the connector body. The check valve restricts fuel back flow.
After the fuel pump flex pipe, the fuel exits the assembly through the fuel feed output fitting on the molded cover. The cover also contains a fuel return provision which connects to one of three hollow support pipes.
Quick-connect pipe end fittings are molded onto the cover of the modular unit for ease of unit removal from the fuel tank. These quick-connect end fittings allow fuel feed and fuel return.
Electrical power to the fuel pump enters the unit by way of a connector which is attached to the cover. An internal wire harness and connector assembly connects to the fuel pump and level sensor. The modular design adds additional functions that improve accuracy and ensure constant, steady fuel supply under all conditions. All components and subassemblies of the modular sender attach to a common cover and access the fuel tank through a single opening. The modular fuel sender assembly is spring loaded to the bottom of the fuel tank. This bottom referencing permits continuous fuel pickup and accurate fuel level sensing. The reservoir assembly is the lower section of the modular unit which encases the fuel pump. A retainer attaches to the top of the reservoir. Fuel is captured and maintained in reservoir at a level sufficient to submerge the fuel pump.