I am going crazy! These websites appear to contradict one another... The lowering of the diaphragm makes the inlet valve of the fuel pump open. With this valve open, fuel is drawn from the gas tank and into the pump. At the same time, the lowering of the diaphragm closes an outlet valve. Read more: How Car Fuel Pumps Work | eHow.com http://www.ehow.com/how-does_5004513_how-car-fuel-pumps-work.html#ixzz1rwSrcgdV A vacuum is created inside the pump casing each time the diaphragm is raised (see figure below). This opens the inlet valve and seals the discharge valve allowing water and air to enter the pump. When the diaphragm is lowered the resulting pressure seals the inlet and opens the outlet valve purging the pump housing of water and air.. http://www.pumps-in-stock.com/diaphragm_pump_designs.html So which way round is it? When the diaphragm is raised does this open the inlet and close the outlet or the reverse or do these pumps work differently?