The carburetor typically contains a float bowl into which the expelled fuel is pumped. When the fuel level in the float bowl exceeds a certain level, the inlet valve to the carburetor will close, preventing the fuel pump from pumping more fuel into the carburetor. At this point, any remaining fuel inside the pump chamber is trapped, unable to exit through the inlet port or outlet port. The diaphragm will continue to allow pressure to the diaphragm, and during the subsequent rotation, the eccentric will pull the diaphragm back to bottom dead center, where it will remain until the inlet valve to the carburetor reopens. Because one side of the pump diaphragm contains fuel under pressure and the other side is connected to the crankcase of the engine, if the diaphragm splits (a common failure), it can leak fuel into the crankcase. The capacity of both mechanical and electric fuel pump is measured in psi (which stands for pounds per square inch). Usually, this unit is the general measurement for pressure, yet it has slightly different meaning, when talking about fuel pumps. Plunger-type pumps are a type of positive displacement pump that contain a pump chamber whose volume is increased and/or decreased by a plunger moving in and out of a chamber full of fuel with inlet and discharge stop-check valves. It is similar to that of a piston pump, but the high-pressure seal is stationary while the smooth cylindrical plunger slides through the seal. These pumps typically run at a higher pressure than diaphragm type pumps. Specific designs vary, but in the most common configuration, these pumps are mounted on the side of the injection pump and driven by the camshaft, either directly or via a pushrod. When the camshaft lobe is at top dead center, the plunger has just finished pushing the fuel through the discharge valve. A spring is used to pull the plunger outward creating a lower pressure pulling fuel into the chamber from the inlet valve. These pumps can run between 250 and 1,800 bar (3,625 and 26,000 psi). Because it is connected to the camshaft, the discharge pressure of these pumps is constant, but the rate at which it pumps is directly correlated to the revolutions per minute (rpm) of the engine. Both pumps create negative pressure to draw the fuel through the lines. However, the low pressure between the pump and the fuel tank, in combination with heat from the engine and/or hot weather, can cause the fuel to vaporize in the supply line.