Analysis & treatment of aircraft air conditioning faults –part I

As the design and manufacturing process of aircraft accessories become more and more mature, the system failures of a certain type of aircraft air-conditioning system due to component failures have decreased year by year, but the proportion of failures caused by system performance degradation and human error has increased year by year with the increase in the frequency of aircraft use.

In the following, we will analyze the common faults such as no ejected air on the ground, no air supply in the cockpit, and little air supply in the cockpit.

No ejection air failure on the ground

During the test run of a certain type of aircraft engine, when checking the working performance of the cabin air conditioning system, it was found that no air was ejected from the exhaust port of the air-air radiator ejector.

1. Cause Analysis

On the ground or in flight with the landing gear down, the air-to-air radiator cools the hot air from the engine's high-pressure compressor by ejecting air from the ejector. After the electromagnetic valve that controls the opening of the ejector shut-off valve is energized, the inner cavity of the ejector shut-off valve is connected to the atmosphere, so that the shut-off valve is opened, and the outside air is ejected into the air-air radiator to dissipate heat from the hot air. According to the working principle of the air-conditioning system and the analysis of the fault phenomenon, the reasons for the lack of ejected air on the ground are as follows:

1) The failure of the electrical circuit that controls the operation of the electromagnetic valve or the failure of the electromagnetic valve itself can cause the pressure difference in the piston cavity of the shut-off valve to not be generated, so that the piston of the ejector shut-off valve cannot overcome the spring force of the valve to open, resulting in no ejected air. .

2) The poor sealing performance of the pipeline between the electromagnetic valve and the intake valve of the ejector shut-off valve, or the blockage of the outlet joint of the electromagnetic valve and the air communication pipeline may cause the pressure difference in the piston cavity of the shut-off valve to not be generated, and the ejector The shut-off valve piston cannot open against the spring force of the valve, resulting in no ejected air.

2. Troubleshooting

1) First disconnect the cable plug connected to the electromagnetic valve, after supplying power to the aircraft, measure whether the No. 3 jack on the cable plug has a voltage of 27±2.7V, and measure whether the No. 1 jack on the cable plug corresponds to the ground. If the voltage and grounding meet the requirements, install the cable plug, and after supplying power to the aircraft, touch the shell of the ejection electromagnetic valve with your hand. If it is hot, it means that the electromagnetic valve is working normally.

2) After eliminating the electrical circuit of the electromagnetic valve or the electromagnetic valve fault, during the engine test run, if there is still no air ejected from the exhaust port of the air-air radiator ejector, it is necessary to check the connection between the electromagnetic valve and the ejector shut-off valve. Check the tightness of the inter-pipeline and whether the electromagnetic valve outlet joint and the atmosphere are blocked.

First, check whether there are defects in the appearance and installation of the pipe joint between the electromagnetic valve intake joint and the ejector shut-off valve that do not meet the requirements for use, and eliminate the related defects found. Then, disconnect the air outlet pipe joint of the electromagnetic valve, blow air from the pipe joint with compressed air, and check whether there is gas ejected from the air vent connected to the pipeline on the engine bulkhead plate. There is a blockage in the pipeline. Disassemble the pipeline to purge the pipeline, remove the blockage of the pipeline, and then reinstall the fixed pipeline to eliminate the fault.