Views: 0 Author: Site Editor Publish Time: 2022-10-05 Origin: Site
No air supply failure in the cockpit
During the engine test run, during the performance inspection of the cabin air supply system, it was found that no air was ejected from the air supply nozzle in the cabin, but air was ejected from the exhaust port of the air-air radiator ejector.
1. Cause Analysis
Since air is ejected from the exhaust port of the air-air radiator ejector, it means that the bleed air system of the left and right engine high-pressure compressors is working normally. According to the working principle of the aircraft air conditioning system, the following reasons may cause the failure of air supply in the cockpit.
1) The "air conditioning signal" circuit breaker on the DC power distribution device is not turned on, the electromagnetic valve of the air-conditioning system is closed, and the electromagnetic valve connecting cable plug is connected incorrectly. Air supply failure.
2) The connection between the control device on the line pressure regulator and the electromagnetic valve that closes the air conditioning system is poorly sealed, which leads to the communication between the bellows cavity of the control device on the line pressure regulator and the external environment, resulting in the upper valve of the control device on the line pressure regulator. Open, make the pressure difference between the two ends of the piston of the shut-off device on the pipeline pressure regulator, and the piston compresses the spring under the action of the pressure difference, so that the air supply adjustment mechanism of the pipeline pressure regulator is closed, resulting in no air supply failure.
3) The line pressure regulator itself is faulty.
According to the analysis of the above fault causes, there are many reasons for "no air supply in the cockpit". When judging the fault, the principle from simple to complex can be adopted, and the cause of the fault can be determined by the elimination method.
1) Check whether the "air conditioner signal" circuit breaker on the DC power distribution device is connected. If it is not connected, it can be judged that the "no air supply in the cockpit" fault is caused by the circuit breaker not being connected. If the "air conditioning signal" circuit breaker on the DC distribution unit is in the ON position, check that the cable plug connected to the solenoid valve for closing the air conditioning system is in the correct position.
Two electromagnetic valves of the same model are installed side by side at this position, one valve is to close the electromagnetic valve of the air conditioning system, and the other valve controls the air-air radiator ejector shut-off valve to open the electromagnetic valve. The electromagnetic valve circuit is normally open, The electromagnetic valve circuit for closing the air conditioning system is normally closed. If the electromagnetic valve cable plug of the ejector closing valve is mistakenly installed on the electromagnetic valve of the closing air conditioning system, the electromagnetic valve of the closing air conditioning system will work, resulting in no air supply failure.
2) Check the appearance status and installation and fixation of the connection between the control device on the pipeline pressure regulator and the electromagnetic valve of the air-conditioning system and whether there are defects that do not meet the requirements. After eliminating the relevant defects found, re-install the fixed conduit.
3) After completing the above two aspects of troubleshooting, carry out the engine test run, turn on the air supply switch in the cockpit, and check whether there is air ejected from the air supply nozzle in the cockpit. If the air supply is normal, it proves that the fault has been eliminated; if there is no air supply, it is determined that the pipeline pressure regulator itself is faulty. Replacing the line pressure regulator can rule out no air supply failure.
Low cockpit air supply failure
During the air flight training of a certain type of aircraft, the pilot reported that the air supply of the cabin air supply system was small during the flight, which affected the working performance of the cabin temperature adjustment system.
1. Failure cause analysis
The bleed air from the high-pressure compressor of the engine is mixed with hot air after three-stage cooling, and is adjusted by the air flow sensor and flow regulator to distribute the air flow to the cabin and the equipment cabin in proportion. The air flow sensor is a venturi. The cold and hot mixed air entering the cabin passes through the flow sensor, and the pressure difference signal formed between the inlet end of the venturi and the outlet end of the throat is transmitted to the flow regulator through the pipeline.
When the differential pressure formed by the flow sensor is P≤10.8+00.49kPa, the valve of the flow regulator is fully open; when the differential pressure P≤8.80-0.49kPa, the valve of the regulator is fully closed. According to the above working principle and failure phenomenon analysis, the following reasons may cause the failure of low air supply in the cockpit.
1) The sealing performance of the connecting pipeline between the flow sensor and the flow regulator is not good, or the pipeline connecting the flow sensor with the air inlet end and the air outlet end of the throat is blocked by foreign matter, which may cause the connection between the air inlet end and the air outlet end of the flow sensor. The air pressure difference formed between them does not meet the requirements, so that the regulating valve of the flow regulator is opened (the normal position of the regulating valve is the closed position), resulting in a reduction in the air supply of the cabin.
2) The failure of the flow regulator itself leads to the wrong ratio of air flow to the cabin and the equipment cabin, resulting in a reduction in the air supply to the cabin.
1) First, check the appearance status and installation and fixation of the connecting pipe joints between the flow sensor and the flow regulator for defects that do not meet the requirements, and then check whether the pipeline joints on the flow sensor and flow regulator are blocked, and eliminate the related findings found. After the defect, reinstall the fixed conduit.
2) Carry out engine test run. Turn on the air supply switch in the cockpit, and check whether the air flow rate from the air supply nozzle in the cockpit is more than that before troubleshooting the pipeline. If there is no change in the air flow rate ejected by the air supply nozzle, it is determined that there is an adjustment failure in the flow regulator, and the failure can be eliminated by replacing the flow regulator.