Created on:2021-10-14 13:35

Hydraulic fault diagnosis and maintenance of airport equipment_ Hydraulic system failure of passenger boarding car

Hydraulic fault diagnosis and maintenance of airport equipment_ Hydraulic system failure of passenger boarding car

Airport passenger boarding car is a kind of on-board equipment with hydraulic transmission and boarding platform that can move up and down and back and forth. It specializes in providing boarding services for passengers. Due to the particularity of its work, the airport puts forward special requirements for boarding locomotives: six legs must be used to support the vehicle, so as to increase the stability and anti overturning performance of the equipment in the process of use; After the work is completed, the boarding car shall be reliably evacuated from the work site to ensure the safety of the aircraft and normal flight.

At present, the passenger boarding car used in the airport, whether imported or domestic, can basically meet the use requirements, but there are still some problems in the use process, especially the hydraulic system. How to solve these problems and make it better serve the airport and ensure the safety of aircraft and passengers, For many years, it has been the goal pursued by airport equipment designers and airport maintenance personnel. The following four aspects are discussed to solve the problems existing in the hydraulic system.

(1) Problems existing in the hydraulic system of the original passenger boarding locomotive

The hydraulic system of airport passenger boarding car adopts open, single pump, quantitative and parallel oil circulation system. The working pressure of the main gear pump is 10MPa and the flow is 40L / min, as shown in Figure I. The main problems are as follows: ① the emergency system only has a manual pump. Once the main gear pump is damaged, only the manual pump can lower the slide and retract the outrigger, which takes a long time and may even delay the flight; ② The six outriggers are fully placed by the pressure relay. Due to the low control accuracy of the pressure relay itself, misoperation occurs from time to time, which poses a potential threat to the safety of passengers; ③ The system is only equipped with one overflow valve. Once the overflow valve fails, all emergency systems will fail, the platform cannot be lowered, the outriggers cannot be retracted, and the boarding car cannot safely evacuate the aircraft, resulting in flight delay; ④ Oil leakage often occurs at the hydraulic lock joint of two straight support hydraulic cylinders.

I.jpg

(2) Fault analysis and treatment of hydraulic system

Figure I shows the schematic diagram of the original hydraulic system. The problems existing in the boarding car are analyzed in detail below.

① Fault phenomenon I after the main gear pump is damaged, the boarding car cannot evacuate the aircraft as soon as possible; Because the emergency system in the original hydraulic system only relies on the manual pump to realize the lowering of the slide and the retraction of the outrigger, it takes a long time and may even delay the flight. For this purpose, an electric pump is added, as shown in Figure J. Once the main gear pump 4 fails to work normally due to the damage of the main gear pump 4 or the failure of other components, start the electric pump 26, quickly lower the push cylinder 16 and stow the front support hydraulic cylinder 19, the straight support cylinder 21 and the inclined support cylinder 22, and then the boarding car can evacuate the aircraft smoothly. With the addition of electric pump 26, the reliability of ground service equipment is greatly enhanced.

② Fault phenomenon II due to the low control accuracy of the pressure relay 20 itself, some supports of the six legs sometimes can not be fully grounded, can not achieve reliable support, and there are great potential safety hazards. Therefore, a set of feedback mechanism is designed to replace the pressure relay 20. As shown in Figure K, the feedback mechanism is composed of upper and lower proximity switches 27, control baffle 28, guide rod 29, fixed seat 31 and straight support left hydraulic cylinder 30. In addition, the inlet and return oil circuit of the hydraulic cylinder is installed. The operation principle is as follows; First, adjust the throttle valve so that the up and down movement speed of the straight support left hydraulic cylinder 30 is lower than that of the other five support cylinders; If the straight support left hydraulic cylinder 30 is fully extended in place, it can ensure that the other five supports are also fully extended in place; If the straight support left hydraulic cylinder 30 is fully retracted in place, it can be ensured that the other five supports are also fully retracted in place. The position shown in the figure is the position where the straight support left hydraulic cylinder 30 is fully retracted in place. When the straight support left hydraulic cylinder 30 moves downward, the guide rod 29 also moves downward and drives the control baffle 28 to move downward. When the control baffle 28 is located in the front of the lower proximity switch, the straight support left hydraulic cylinder 30 is fully extended in place; vice versa.

KL.jpg

③ Fault phenomenon III once 7 there is a fault, all emergency systems will fail. When the electromagnetic overflow valve 7 fails, such as the overflow valve core is stuck at the large opening position, the pressure oil output by the hydraulic pump flows back to the oil tank through the overflow valve, that is, the pressure oil is short circuited with the return oil circuit, or the pressure regulating spring is broken, resulting in no pressure in the system. At this time, it will be impossible to lower the slide and retract the outrigger, resulting in flight delay. Because the overflow valve is one of the components that are easy to fail. Therefore, in order to prevent this accident, an overflow valve 32 is added to the system, as shown in Figure L. In actual work, the pressure of overflow valve 32 is 2 ~ 3Mpa higher than that of overflow valve 7. In this way, once overflow valve 7 fails, the subsequent stop valve will be closed, and overflow valve 32 will automatically enter the working state, which will not affect the normal operation of the system.

④ Fault phenomenon IV: there is often oil leakage at the hydraulic lock joint of two straight support hydraulic cylinders. Oil leakage mainly occurs at the connection between the pipe joint and the hydraulic lock, and at the connection between the end cover of the hydraulic lock and the valve body.

The improved hydraulic system has achieved good results in the user's use, achieved the expected purpose, and the safety of the whole machine has been improved.

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