R EFF : 001-049, 101-105, 107-107, 151-199, 49-51-00Page 6 201-210, Config-2 Aug 01/05
CES The main unit is the Surge Control Valve (SCV). The SCV is installed on the tee-duct in the aft direction to direct excessive bleed air overboard through the APU exhaust. The SCV is a hydraulic ally actuated butterfly valve, which is normally spring loaded open. A hydraulic ally operated actuator, controlled by an electrohydraulic servo valve, opens or closes the valve. The hydraulic power is supplied by the high pressure side of the FCU. The ECB controls the servo valve, via a torque motor, to open or close the butterfly valve of the SCV. An LVDT provides position feedback to the ECB. The air pressure developed by the load compressor is sampled by the static pressure and total pressure probes. The Total Pressure transducer (PT) and the Delta Pressure (DP) transducer translate the pressure inputs into an electrical signal which are transmitted to the ECB. Surge protection is controlled by the ECB. The ECB compares a corrected airflow and a surge margin set point. The corrected airflow is the amount of air that flows through the load compressor. The ECB calculates the corrected airflow using the signals of the PT transducer and the DP transducer. The surge margin set point is the minimum amount of air that should flow from the load compressor for APU operation condition. The surge margin set point is a function of the inlet temperature (T2), the inlet pressure (P2), the total pressure (PT), the delta pressure (dP) and the IGV position and the aircraft selected mode. If the surge margin set point is more than the corrected air flow the ECB triggers the SCV to open. This keeps the airflow from the load compressor at the minimum level.
4. Interface_________ (Ref. Fig. 005) The bleed and surge air system has an interface with:
-
the APU Bleed Air Supply and Crossbleed System (Ref. 36-12-00),
-
the APU Load Compressor (Ref. 49-23-00),
-
the Control and Monitoring System (Ref. 49-61-00).
5. Component Description_____________________
A. Surge Control Valve (SCV) The SCV is a hydraulically actuated butterfly valve with a position feedback from a linear variable differential transformer (LVDT) to the ECB. The SCV has also a visual position indicator. Fuel pressure is routed to the spool valve and through the filter to the operating jet. With zero current applied to the torque motor, the torque motor is biased to supply high pressure and low pressure to the spool valve. The spool valve moves in relation to the pressure applied and allows pressure to open the valve. As current is applied to the torque motor, more pressure is applied to the spool valve. This results in the valve stroking towards the closed position.
R EFF : 001-049, 101-105, 107-107, 151-199, 49-51-00Page 7 201-210, Config-2 Aug 01/05
CES
Bleeed and Surge Air - Interface
Figure 005
CES Loss of the electrical signal (open circuit) will disable the SCV to the fully open position.
B. Load Control Valve The Load Control Valve (LCV) is a pneumatically actuated open butterfly valve. The valve flow section is made up of a valve body, a butterfly shaft and a butterfly plate. The valve body is a cylindrical air-flow duct, flanged at each end, for in-line installation with the air ducts. Flanges at the top and bottom of the valve body each have an axially-aligned bore for the butterfly shaft. The butterfly shaft is bearing mounted across the valve body and extends upward through the top of the actuator. The butterfly plate (attached to the butterfly shaft) operates as a spring-loaded air-flow flap inside the valve body. The position-indicator switch assembly (installed on top of the pneumatic actuator) has:
-a switch lever,
-two switches,
-an electrical receptacle,
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