Typical fuel dispensers include several sections, such as hydraulic, metering, and hose/nozzle portions. The hydraulic section contains a rotary pump for drawing fuel from the storage tank and a solenoid/pilot valve to ensure that fuel flows only toward the dispenser and not back into the pump. Commercial dispensers such as those found at gas/petrol stations may house multiple units connected to different storage tanks for the purpose of supplying multiple fuels with different compositions or octane ratings.
An operational fuel dispenser contains a continuously running electric motor between the storage tank and the hydraulics portion of the unit for the purpose of maintaining a partial vacuum at the rotary pump inlet. When the nozzle opens, the storage tank draws suction pressure from the inlet, causing fuel to flow toward the pumping unit. An intermediary filter removes air bubbles or suspended solids from the fuel.
Fuel then flows through the pump and valve and into the metering unit. This portion includes mechanical gearboxes, as in older pumps, or piston meters and encoders to measure and distribute a specified amount of fuel or track fuel output. After the metering section, the fuel progresses through a flexible hose and into a nozzle that dispenses it into a vehicle or storage tank.
Fuel dispensers range from large commercial gas pumps to simple dispenser pumps for use with portable storage tanks.