Plunger Type Electric Fuel Pump

Due to the high cost of the electric centrifugal booster pump, the fuel system of many small lower monoplanes adopts the electric plunger pump as the auxiliary fuel pump of the fuel system. Piston pumps are usually installed in parallel with engine driven diaphragm fuel pumps so that they individually or collectively supply fuel to the engine.

The plunger type fuel pump is a pulsating pump, which consists of a solenoid coil, a plunger, a calibration spring and two one-way valves (nets 9-14). The solenoid coil is wound on a brass tube connecting the 2 oil chambers. The spring force of the calibration spring pushes the plunger up, and the electromagnetic force of the coil pushes the plunger down. A one-way valve is installed in the middle of the plunger, and the other is installed in the middle of the bottom of the brass tube extension in the oil inlet chamber.

When the plunger pump is not energized, the calibrated spring force pushes the plunger up the brass tube and the plunger will attract the magnets that make contact through the pivot. When energized, current flows through the magnet wire through the contacts to create an electromagnetic force that draws the plunger down into the coil section. At this time, the fuel in the B cavity flows upward to the plunger through the one-way valve. When the plunger moves down to the middle of the solenoid, the magnet will no longer be attracted, the contacts will trip, and the solenoid will be de-energized. Electromagnetic force disappears. At this time, the calibration spring pushes the plunger up, and the fuel in the C cavity is squeezed out and supplied to the engine. At the same time, the fuel from the fuel tank is drawn into the A cavity, and then enters the B cavity through the bottom one-way valve to prepare for the next fuel supply cycle.

If the engine is receiving the full output of the pump, the pump will pulsate at a high frequency; however, if the engine carburetor idle valve is closed, or if there is fuel pressure between the carburetor and the pump, the pump will be low pulsing.