top  of  the  large  diaphragm  combine  to  hold  the valve  closed. When the solenoid is energized, air supplied to chamber B bleeds off through the solenoid and the butterfly valve opens. As the butterfly valve opens, air pressure from the downstream side of the  valve  is  applied  to  the  bottom  of  the  pilot regulator diaphragm. This unseats the regulator valve  stem  and  permits  upstream  air  to  flow  to chamber B. As the downstream pressure varies, a varying amount of air is metered by the pilot regulator   valve   to   chamber   B.   The   metering positions the diaphragm and the butterfly valve to maintain the proper downstream pressure. If the downstream pressure increases to a value in excess  of  the  regulator  setting,  the  pilot  valve opens. When this occurs, the solenoid valve is not capable  of  bleeding  off  the  increased  airflow  in chamber  B.  Therefore,  chamber  B  pressure  in- creases,  and  the  butterfly  valve  moves  toward  the closed   position   until   regulation   pressure   is reached. RAIN-REMOVAL NOZZLE ASSEMBLY.— The rain-removal nozzle assembly consists of two ejectors, a plenum chamber, and 26 nozzles. The bleed-air duct has two nozzles aligned with and located  beneath  each  ejector  tube.  The  ejectors mix cool air from the nose radome compartment with the hot bleed air. The mixture is distributed by the plenum to the nozzles, which results in a wide  stream  of  air  across  the  windshield.  The plenum  chamber  provides  an  approximately  equal pressure at each nozzle. The rain-removal nozzle assembly is beneath the left windshield, WINDSHIELD  SWITCH.—  The windshield switch   is   a   single-pole,   three-position   switch mounted on the air-conditioning control panel in the  cockpit.  The  three  positions  are  OFF,  AIR, and  WASH.  This  switch  controls  the  operation of  the  windshield-washing  shutoff  valve  and  rain- removal   pressure-regulator   shutoff   valve.   The switch is spring-loaded to the OFF position. The AIR  and  WASH  positions  are  momentary  con- tacts.  If  the  switch  is  placed  in  the  WASH position,  it  directs  streams  of  washing  fluid against the base of the windshield. If it is placed to  the  AIR  position,  it  directs  a  wide  stream  of hot air across the glass. NOSEWHEEL   WELL   BLEED-AIR SWITCH.— The nosewheel well bleed-air switch is a single-pole, two-position switch mounted on the  fuel  management  panel  in  the  cockpit.  The two  positions  are  OFF  and  AUTO.  This  switch controls  the  operation  of  the  nosewheel  well  bleed- air shutoff valve. Placing the switch in the OFF position  closes  the  nosewheel  well  bleed-air shutoff  valve.  When  the  switch  is  set  to  AUTO position,  the  nosewheel  well  bleed-air  shutoff valve will open when the rain-removal system is energized  or  when  the  left  main  landing  gear weight-on-wheels  switch  is  actuated. NOSEWHEEL   WELL   BLEED-AIR   RE- LAY.—  The  nosewheel  well  bleed-air  relay  is  a double-pole,  double-throw,  relay  mounted  in  aft bay  relay  box  No.  3.  Its  operation  is  controlled by the windshield switch on the air-conditioning panel or by the left main landing gear weight-on- wheels  switch.  When  energized,  the  relay  com- pletes a 115-volt ac circuit to open the nosewheel well bleed-air shutoff valve. When de-energized, the relay completes a 115-volt ac circuit to close the  nosewheel  well  bleed-air  shutoff  valve. LEFT  MAIN  LANDING  GEAR  WEIGHT- ON-WHEELS SWITCH.—  The  left  main  landing gear  weight-on-wheels  switch  is  a  double-pole, double-throw  switch  mounted  on  the  lower  torque arm  of  the  left  gear  shock  strut.  The  switch  is closed  when  the  shock  strut  piston  is  extended. When  the  shock  strut  piston  is  compressed,  the plunger of the switch is fully extended. When the switch plunger is extended, a 28-volt dc circuit is completed to energize the nosewheel well bleed- air relay. WINDSHIELD   RAIN-REMOVAL   WARN- ING  RELAY.—  The   windshield   rain-removal warning”  relay  is  a  double-pole,  double-throw, sealed  relay  mounted  in  the  cockpit  center  console below  the  wing  fold  panel.  Its  operation  is controlled  by  the  windshield  switch  on  the  air- conditioning panel. When the windshield switch is  in  the  AIR  position,  28  volts  of  dc  power  is directed from the air-conditioning circuit breaker to energize the relay and illuminate the windshield air caution light. The relay is de-energized when the windshield switch is set to OFF. At this time, the  windshield  air  caution  light  will  go  out. WINDSHIELD  AIR  CAUTION  LIGHT.— The windshield air caution light is located on the caution light panel in the cockpit. It illuminates to  indicate  that  the  windshield  switch  is  in  the AIR   position.   The   operation   of   the   light   is controlled  by  the  windshield  rain-removal  warning relay. 3-9