are basically the same as the manually operated valves, but  electric motors are used to actuate the units. The two most  common electric motor operated fuel valves are the gate valve  and the plug-type valve.  A single selector valve is not used in complex fuel systems  of transport category aircraft. Fuel flow is controlled with a  series of ON/OFF, or shutoff, type valves that are plumbed  between system components. Hand-operated gate valves  can be used, especially as fire control valves, requiring no  electrical power to shutoff fuel flow when the emergency fire  handle is pulled. The valves are typically positioned in the fuel  feed line to each engine. Hand-operated gate valves are also  featured as ground-operated defuel valves and boost pump  isolation valves, which shut off the fuel to the inlet of the boost  pump, allowing it to be changed without emptying the tank. The motor-operated gate valve uses a geared, reversible  electric motor to turn the actuating arm of the valve that  moves the fuel gate into or out of the path of the fuel. As with  the manually operated gate valve, the gate or blade is sealed.  A manual override lever allows the technician to observe the  position of the valve or manually position it.  [Figure 14-44] Less common is the use of a motorized plug-type fuel valve;  an electric motor is used to rotate the plug or drum rather than  it being rotated manually. Regardless of the type of valve  used, large aircraft fuel system valves either allow fuel to  flow or shut off flow.  Gate valves utilize a sealed gate or blade that slides  into the path of the fuel, blocking its flow when closed.  Figure 14-43  shows a typical hand-operated gate valve.  When the handle is rotated, the actuating arm inside the valve  moves the gate blade down between seals and into the fuel  flow path. A thermal relief bypass valve is incorporated to  relieve excess pressure buildup against the closed gate due  to temperature increases. The use of electric motors to operate fuel system valves is  common on large aircraft due to the remote location from the  cockpit of fuel system components. The types of valves used  An additional way to operate a remotely located fuel valve  is through the use of electric solenoids. A poppet-type valve  is opened via the magnetic pull developed when an opening  solenoid is energized. A spring forces a locking stem into  a notch in the stem of the poppet to lock the valve in the  open position. Fuel then flows through the opening vacated  by the poppet. To close the poppet and shut off fuel flow, a  closing solenoid is energized. Its magnetic pull overcomes  the force of the locking stem spring and pulls the locking  Figure 14-44.  An electric motor-driven gate valve commonly used  in large aircraft fuel systems. Figure 14-43.  A hand-operated gate valve used in transport category  aircraft fuel systems. Manually-Operated Gate Valves Solenoid-Operated Valves Motor-Operated Valves Roller Actutating arm Blade Mounting plate Index pin O-Ring Seals Thermal relief valve Valve handle attached here Housing Gear train actuator Motor Manual override lever Housing Thermal relief valve O-ring Roller Arm Blade Seals 14-27