Created on:2021-10-14 13:35

Maintenance of airport ground equipment_ Improvement of hydraulic system of support foot

Maintenance of airport ground equipment_ Improvement of hydraulic system of support foot

There are more and more high-altitude ground equipment used in airports, such as aircraft deicing truck, boarding elevator, food truck, aerial work vehicle, etc. these equipment are on-board equipment modified from automobile chassis. When in use, there must be four rigid support points (two on the left and right sides of the front and rear positions of the vehicle) to support the vehicle, So as to increase the stability and anti overturning performance of the equipment during use. Because these equipment work close to the aircraft, they are required to leave the work site quickly after the work is completed to ensure normal flight. If the support foot fails and cannot be eliminated in a short time, and the equipment cannot leave the site, it is bound to delay the flight and cause accidents, which puts forward higher requirements for the reliability of the support foot.

(1) Problems existing in the hydraulic system of supporting feet currently used

The currently used support foot hydraulic system (Figure n) adopts each hydraulic cylinder with its own hydraulic lock, which is controlled by one. The electromagnetic directional valve is Y-type valve and the overflow valve is. When the electromagnetic directional valve is energized, the electromagnetic overflow valve is energized at the same time, and the system establishes pressure and starts to act. The utility model has the advantages of simple structure and high reliability. However, some problems are also found in the actual use process.

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① The operation automation is low. During the operation, the control button of the electromagnetic directional valve must be pressed until the four support feet are fully extended (or retracted). Pressing the button for a long time is easy to cause fatigue of the button mechanical structure and shorten the service life; At the same time, since it is impossible to directly observe the extended (or retracted) position of the support foot, it can only be judged by experience (such as listening to the overflow noise of the engine or overflow valve). This judgment is very inaccurate because the airport ground noise is very loud. Often, the support foot has been fully extended (or retracted), and the operation of extending (or retracting) the support foot is still in progress, so that the system is in the overflow state, It causes the system to heat, reduces the viscosity of hydraulic oil, accelerates the oxidation of hydraulic oil, and reduces the efficiency and reliability of the whole system.

② Without considering the emergency treatment, the reliability of the hydraulic system largely depends on the cleanliness of the oil. The pollutants in the oil are easy to cause the electromagnetic directional valve and hydraulic lock to be stuck, which will lead to the failure to retract after the support foot is extended, and the whole equipment will not be able to move due to the landing of the support foot and cannot exit the work site, which is bound to delay the flight and cause accidents.

(2) Solution

In order to improve the automation of the operation process and improve the emergency handling capacity of the whole vehicle, the centralized hydraulic lock is adopted, the extension (retraction) of the support foot is controlled through the pressure relay, the leakage free needle valve is installed, and the support foot is retracted by the hand pump. As shown in Figure m, it has the following advantages.

① Improve the automation degree of the operation process, press the extension (or retraction) button of the support foot to control the electromagnetic directional valve and the electromagnetic overflow valve to pull in the relay contact of the electromagnet, the electromagnetic directional valve and the electromagnetic overflow valve act, and the support foot begins to extend (or retract). At this time, the system pressure is lower than the set pressure of the pressure relay, and the pressure relay is closed; When the support feet are fully extended (or retracted), the system pressure rises above the set pressure of the pressure relay, the pressure relay is disconnected, the electromagnetic directional valve and electromagnetic overflow valve are powered off, the action stops, and the system is in the unloading state. In order to prevent the impact of system pressure impact on the pressure relay, the action of the relay controlling the solenoid directional valve and solenoid overflow valve electromagnet is delayed by 2 ~ 3S through the electrical system to ensure the normal operation of the system.

② Improve the emergency handling capacity. When the electromagnetic directional valve or hydraulic lock is stuck and the support foot cannot be retracted after extending, the needle valve can be opened, and the rodless cavity of the hydraulic cylinder can be directly connected with the oil tank. The support foot can be retracted quickly by using the hand pump to evacuate the site to avoid flight delay. However, the problem caused by the use of centralized hydraulic lock is that in case of pipeline rupture, it will lead to rapid recovery of support feet, and a major accident of vehicle tilting or even overturning will occur, with unimaginable consequences. Based on the above reasons, the original pipeline is reconstructed, and the speed limiting shut-off valve is installed on the hydraulic cylinder of the support foot, as shown in Figure o. In case of accidents such as pipeline burst, it can quickly and automatically shut off the oil circuit to prevent danger, and will not affect the above emergency treatment functions.

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Since adopting the advanced system of centralized hydraulic lock shown in Figure o, controlling the expansion and contraction of support foot through pressure relay and installing speed limiting shut-off valve, there has been no flight delay accident for airport equipment such as aircraft deicing truck, boarding passenger elevator, aircraft food truck and aerial work vehicle.

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