NOSEWHEEL WELL BLEED-AIR SHUT-OFF VALVE.- The nosewheel well bleed-air

Figure 3-7.-Air-conditioning panel. shutoff valve is a butterfly-type that is 3-7

electrically actuated and operated. The valve is installed in the hot bleed-air duct in the starboard engine compartment. The valve is controlled by the nosewheel well bleed-air switch on the fuel management panel. When the switch is set to the OFF position, the valve is closed by 115-volt ac power from the bleed-air circuit breaker. When the switch is set to the AUTO position, power is routed to the nosewheel well bleed-air relay. When the windshield switch on the air-conditioning panel is moved to the AIR position, or when left main landing gear weight-on-wheels switch is closed, the relay is activated and the valve opens. If electric power is lost, the valve will remain in the last selected position. The valve has a position indicator that can be viewed with the starboard engine-bay door open.

RAIN-REMOVAL PRESSURE-REGULATOR SHUTOFF VALVE.- The rain-removal pressure-regulator shutoff valve is a pneumatically operated, solenoid-controlled, 2-inch valve installed in the hot bleed-air duct to the rainremoval nozzle assembly. (See fig. 3-8.) Operation of the valve is controlled by the windshield switch on the air-conditioning control panel. Placing the switch to the AIR position energizes the solenoid of the valve. When the inlet pressure to the valve is between 15 and 50 psi, the valve is fully opened. When it is between 100 and 250 psi, the valve regulates the outlet pressure to the rain-removal nozzle at 753.5 psi. By placing the windshield switch to OFF, it de-energizes the solenoid. This causes the valve to close and shuts off the flow of bleed air to the rain-removal nozzle.

In the closed position, air from the upstream side of the valve passes through the control air passages to chamber A and leaks past the pilot valve stem to chamber B. With equal pressure on both sides of the large diaphragm, the pressure on the small diaphragm and the spring force on

Figure 3-8.-Rain-removal Pressure-regulator shutoff valve. 3-8

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 increases, and the butterfly valve moves toward the closed position until regulation pressure is reached.