A fuel level control valve/system controls the quantity of fuel in a tank being filled or emptied on the aircraft. This document provides a general familiarization with these mechanisms (e.g., forms they take, functions, system design considerations). This document provides the aircraft fuel system designer with information about these mechanisms/devices, so that he can prescribe the types of level control valves/systems which are best suited for his particular fuel system configuration. The scope has been expanded as different aircraft manufacturers may use different type of fuel system architectures. Their refueling and defueling systems may take different configurations, may require different types of fuel control valves and may require different types of interface with the onboard Fuel Measurement System. They must also limit pressure surges and be compatible with ground refueling equipment which have varying surge potentials and create surges.