GR DUMP V switch, located on the cockpit overhead panel.  A dump valve reset switch is used to reset the dump valve  after the system has been used and serviced. 1. Landing gear handle is placed in the DOWN position. 2. Red light in the landing gear control handle is  illuminated. 3. EMER LDG GEAR handle is pulled fully outward. 4. Compressed nitrogen is released to the landing gear  selector/dump valve. 5. Pneudraulic pressure actuates the dump valve portion  of the landing gear selector/dump valve. 6. Blue DUMP legend is illuminated on the LDG GR  DUMP switch. 7. Landing gear system is isolated from the remainder  of hydraulic system. 8. Pneudraulic pressure is routed to the OPEN side of  the landing gear door actuators, the UNLOCK side of  the landing gear uplock actuators, and the EXTEND  side of the main landing gear sidebrace actuators and  nose landing gear extend/retract actuator. 9.  Landing gear doors open. 10. Uplock actuators unlock. 11. Landing gear extends down and locks. 12. Three green DOWN AND LOCKED lights on the  landing gear control panel are illuminated. 13. Landing gear doors remain open. A medium-pressure pneumatic system (50–150 psi) usually  does not include an air bottle. Instead, it generally draws air  from the compressor section of a turbine engine. This process  is often called bleed air and is used to provide pneumatic  power for engine starts, engine deicing, wing deicing, and in  some cases, it provides hydraulic power to the aircraft systems  (if the hydraulic system is equipped with an air-driven  hydraulic pump). Engine bleed air is also used to pressurize  the reservoirs of the hydraulic system. Bleed air systems are  discussed in more detail in the powerplant handbook. Many aircraft equipped with reciprocating engines obtain  a supply of low-pressure air from vane-type pumps. These  pumps are driven by electric motors or by the aircraft engine.  Figure 12-77  shows a schematic view of one of these pumps,  which consists of a housing with two ports, a drive shaft, and  two vanes. The drive shaft and the vanes contain slots, so  the vanes can slide back and forth through the drive shaft.  The shaft is eccentrically mounted in the housing, causing  the vanes to form four different sizes of chambers (A, B, C,  and D). In the position shown, B is the largest chamber and  is connected to the supply port. As depicted in  Figure 12-77, outside air can enter chamber B of the pump. When the  pump begins to operate, the drive shaft rotates and changes  positions of the vanes and sizes of the chambers. Vane No.  1 then moves to the right, separating chamber B from the  supply port. Chamber B now contains trapped air.  As the shaft continues to turn, chamber B moves downward  and becomes increasingly smaller, gradually compressing its  air. Near the bottom of the pump, chamber B connects to the  pressure port and sends compressed air into the pressure line.  Then chamber B moves upward again becoming increasingly  larger in area. At the supply port, it receives another supply  of air. There are four such chambers in this pump and each  goes through this same cycle of operation. Thus, the pump  delivers to the pneumatic system a continuous supply of  compressed air from 1 to 10 psi. Low-pressure systems are  used for wing deicing boot systems. Maintenance of the pneumatic power system consists of  servicing, troubleshooting, removal, and installation of  components, and operational testing. The air compressor’s lubricating oil level should be checked  daily in accordance with the applicable manufacturer’s  instructions. The oil level is indicated by means of a sight gauge  or dipstick. When refilling the compressor oil tank, the oil (type  specified in the applicable instructions manual) is added until  the specified level. After the oil is added, ensure that the filler  plug is torqued, and safety wire is properly installed. Medium-Pressure Systems Low-Pressure Systems  Pneumatic Power System Maintenance 12-52 Figure 12-77.  Schematic of vane-type air pump. C h a m b e r  A C h a m b e r D C h a m b e r  C $_{ }$C h a m b e r B Supply port Pressure port Housing Vane 2 Vane 1 Drive shaft Emergency Extension Sequence: