Chemical Drier Emergency Backup Systems Gear Emergency Extension Cable and Handle Nitrogen Bottles Dump Valve Figure 12-76.  Pneumatic emergency landing gear extension system. 12-51 Nose wheel steer NWS cont valves Power WOW inputs GRND serv valve (GRND only) R SYS Anti skid valves (4) Wheel brakes (4) Park brake valve Landing gear/doors N$_{2 }$CYLS (2) Landing gear dump valve Outlet & vent valve Landing gear handle inputs LDG gear select valve Brake pedal inputs AUGM enter valve Brake cont  valves (2) E M E R L D G G E A R N$_{2}$ HYD Auxilliary pump Park/emergency brake accum Park/ emergency brake Auxilliary SOV Auxilliary boost pump Not APM ON Power transfer unit  OFF ON Not APM ON Auxillary pump System accum (ASC D7) System accum (ASC D7) OFF ON Landing Gear PUMP V N$_{2}$ H Y D N$_{2}$ H Y D pump R 1 2 DISCH L 1 2 DISCH L SYS AUX Disconnected with ASC 87 Right engine pumps Left engine pumps Disconnected with ASC 87 L SYS R SYS PTU AUX Check valve L SYS/PTU L SYS/PTU/AUX NITROGEN (N$_{2}$) Control Shutoff valve Chemical driers are incorporated at various locations in a  pneumatic system. Their purpose is to absorb any moisture  that may collect in the lines and other parts of the system.  Each drier contains a cartridge that should be blue in  color. If otherwise noted, the cartridge is to be considered  contaminated with moisture and should be replaced. by actuation of an outlet valve. Once depleted, the bottles  must be recharged by maintenance personnel. Fully serviced  pressure is approximately 3,100 psi at 70 °F/21 °C, enough  for only one extension of the landing gear. The outlet valve is connected to a cable and handle assembly.  The handle is located on the side of the copilot’s console  and is labeled EMER LDG GEAR. Pulling the handle fully  upward opens the outlet valve, releasing compressed nitrogen  into the landing gear extension system. Pushing the handle  fully downward closes the outlet valve and allows any  nitrogen present in the emergency landing gear extension  system to be vented overboard. The venting process takes  approximately 30 seconds. Many aircraft use a high-pressure pneumatic back-up source  of power to extend the landing gear or actuate the brakes,  if the main hydraulic braking system fails. The nitrogen is  not directly used to actuate the landing gear actuators or  brake units but, instead, it applies the pressurized nitrogen  to move hydraulic fluid to the actuator. This process is  called pneudraulics. The following paragraph discusses the  components and operation of an emergency pneumatic landing  gear extension system used on a business jet.  [Figure 12-76] As compressed nitrogen is released to the landing gear  selector/dump valve during emergency extension, the  pneudraulic pressure actuates the dump valve portion of  the landing gear selector/dump valve to isolate the landing  gear system from the remainder of hydraulic system. When  activated, a blue DUMP legend is illuminated on the LDG  Nitrogen used for emergency landing gear extension is  stored in two bottles, one bottle located on each side of  the nose wheel well. Nitrogen from the bottles is released 