The flow modulating system pressure regula-tor valve is a combination butterfly, modulating valve, and solenoid shutoff valve. The modulating valve is normally open and pneumatically actuated. The valve is in the distribution ducting between the primary heat exchanger and the refrigeration turbine/ compressor assembly. The valve uses electrical signals from the avionics temperature/ flow sensor by way of the ACS temperature/ flow controller to modulate down-stream pressure. The valve is also connected pneumatically to the turbine and compressor protective temperature sensors, which override all other valve functions to close the valve to protect the refrigeration turbine/ compressor assembly from heat damage during overtemper-ature conditions. The solenoid shutoff is con-trolled by the environmental control system (ECS) mode switch, which allows the valve to be opened or closed by dumping control air from the butter-fly diaphragm chamber. The valve also includes a visual position indicator. The indicator is built into the valve housing and shows the position of the butterfly.

Avionics Ram Air Servo

The avionics ram air servo monitors the differential pressure of bleed air upstream and downstream of the flow modulating system pressure regulator valve. If the upstream -pre s s ure is less than 35 psi and the differential pressure is less than 10 psi, the avionics ram air servo drives the avionics ram air valve open. If downstream pressure is less than 4 psi, the avionics ram air servo drives the avionics ram air valve open. The operation of this valve, though not a part of the ACS, ensures that avionics will receive sufficient cooling air in the event of a low or no airflow condition from the ACS.

Compressor Protective Temperature Sensor

The compressor protective temperature sensor is a pneumatic bleed off thermostat, which contains a fluid-filled sensing element and a ball metering valve. The unit is in the duct up-stream of the turbine/ compressor assembly. The thermostat is connected pneumatically to the flow modulation system pressure regulator valve and responds to air temperature. As the air temper-ature increases, the fluid in the sensing element expands and opens the ball metering valve, which vents control pressure from the flow modulating valve. This causes the regulator to close, de-creasing the bleed-air flow, which slows the rpm of the turbine assembly, thus protecting it from damage because of overtemperature.

Turbine Protective Temperature Sensor

The turbine protective temperature sensor is identical to the compressor protective temperature sensor except for calibrated temperature and location. The turbine protective temperature sensor is in the turbine inlet duct.