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