Pressure relief valves Outlet Aft From boost pump Out to engine Air bleed line Low sump level switch Flapper valves Check valve Suction line Tank wall Tank Boost pump Inboard Ejector pumps Figure 14-51.  An ejector pump uses a venturi to draw fuel into the boost pump sump area of the fuel tank. Vane-Type Fuel Pumps As the plunger rises, the magnet is attracted to it and the  upward motion closes the points. This allows current flow  to the solenoid coils, and the process begins again with the  plunger pulled down between the coils, the magnet releasing,  and the points opening. The single-acting pulsating electric fuel pump responds to  the pressure of the fuel at its outlet. When fuel is needed,  the pump cycles rapidly with little pressure at the pump  outlet. As fuel pressure builds, the pump slows because the  calibrated spring meets this resistance while attempting to  force the piston upwards. A spring in the center of the plunger  dampens its motion. A diaphragm between the chamber D  fuel and an airspace at the top of the pump dampens the  output fuel pulses.  the same manner as a centrifugal fuel pump on larger aircraft,  except it is located downstream of the fuel tank outlets. The  pulsating electric fuel pump is plumbed in parallel with the  engine-driven pump. During starting, it provides fuel before  the engine-driven fuel pump is up to speed, and it can be  used during takeoff as a backup. It also can be used at high  altitudes to prevent vapor lock. The pulsating electric pump uses a plunger to draw fuel in  and push fuel out of the pump. It is powered by a solenoid  that alternates between being energized and de-energized,  which moves the plunger back and forth in a pulsating  motion.  Figure 14-52  shows the internal workings of the  pump. When switched ON, current travels through the  solenoid coils, which pull the steel plunger down between  the coils. Any fuel in chamber C is forced through the small  check valve in the center of the plunger and into chamber  D. When positioned between the solenoid, the plunger is far  enough away from the magnet that it no longer attracts it,  and the pivot allows the contacts to open. This disrupts the  current to the solenoid.  Vane-type fuel pumps are the most common types of fuel  pumps found on reciprocating-engine aircraft. They are used  as both engine-driven primary fuel pumps and as auxiliary or  boost pumps. Regardless, the vane-type pump is a constant  displacement pump that moves a constant volume of fuel  with each revolution of the pump. When used as an auxiliary  pump, an electric motor rotates the pump shaft. On engine- driven applications, the vane pump is typically driven by the  accessory gear box. The calibrated spring shown under the plunger is then strong  enough to push the plunger up from between the solenoid  coils. As the plunger rises, it pushes fuel in chamber D out  the pump outlet port. Also, as the plunger rises, it draws fuel  into chamber C and through the check valve into chamber C. 14-31