Grommet Support tube at least $^{1}$/4 inch from edge of hole Bonded cushion clamp 14-25 Figure 14-38.  Detents for each position, an indicating handle, and  labeling aid the pilot in knowing the position of the fuel valve.  Figure 14-37.  Rigid metallic fuel lines are clamped to the airframe  with electrically bonded cushion clamps at specified intervals. Figure 14-36.  Exterior fuel hose wrap that protects from fire, as well as abrasion, shown with the clamps and pliers used to install it. Hand-Operated Valves There are three basic types of hand-operated valves used in  aircraft fuel systems. The cone-type valve and the poppet- type valve are commonly used in light general aviation  aircraft as fuel selector valves. Gate valves are used on  operated valves accomplish this through the use of detents  into which a spring-loaded pin or similar protrusion locates  when the valve is set in each position. Combined with labels  and a directional handle, this makes it easy to identify by  feel and by sight that the valve is in the desired position.  [Figure 14-38]  Motor- and solenoid-operated valves use  position annunciator lights to indicate valve position in  addition to the switch position. Flight management system  (FMS) fuel pages also display the position of the fuel valves  graphically in diagrams called up on the flat screen monitors.  [Figure 14-39]  Note that many valves have an exterior  position handle, or lever, that indicates valve position. When  maintenance personnel directly observe the valve, it can be  manually positioned by the technician using this same lever.  [Figure 14-40] incorporates the shutoff and selection features into a single  valve. Large aircraft fuel systems have numerous valves.  Most simply open and close and are known by different  names related to their location and function in the fuel  system (e.g., shutoff valve, transfer valve, crossfeed valve).  Fuel valves can be manually operated, solenoid operated, or  operated by electric motor.  A feature of all aircraft fuel valves is a means for positively  identifying the position of the valve at all times. Hand- Approximate distance between  supports (inches) Tubing OD (inch)  9 12 16 22 30 40 $^{3}$/16 $^{5}$/16 $^{1}$/2 $^{3}$/4 1$^{1}$/4 2 $^{1}$/8 $^{1}$/4 $^{3}$/8 $^{5}$/8 7 1$^{1}$/2 to to to to to to