Why Pneumatic Systems Are Important For Aircraft

Pneumatic systems are quite common to a number of industries, often used for dentist tools, factory machines, paint sprayers, and much more. A pneumatic system is quite comparable to a hydraulic system, albeit utilizing pressurized gases in lieu of pressurized fluids. When equipped on an aircraft, a pneumatic system can be used for the transmission of power for the means of operating brakes, doors, emergency devices, and driving systems.

In order for energy to be sufficiently transferred through pneumatic gas, it must be compressed within an enclosed space. While the fluids of a hydraulic system are nearly incompressible, gases are highly compressible. Nevertheless, such systems are designed so that gas can be pressurized within a space to meet the air pressure requirements of the aircraft. For typical high-pressure systems, gases are stored within metal bottles which maintain a pressure ranging from 1,000 to 3,000 psi. Two valves are then provided on these bottles, one of which comes in the form of a charging valve. With the use of a ground-operated compressor, air can be supplied to the canister with the use of the charging valve. The control valve is the other valve, that of which prevents any gas from escaping the bottle until needed.

While an air bottle is typically quite lightweight, they are limited in the amount of gas that they may store and cannot be recharged mid-flight. Due to this fact, they are typically reserved for emergency situations due to their small supply. This is beneficial for deploying landing gear or brakes when other power systems fail, furthering the safety and redundancy of the aircraft.

Despite their similarities to hydraulic systems, the general makeup of pneumatic systems can differ due to how they handle power transfer. Air compressors are one of the major components of such assemblies, permanently installed in order to recharge certain air bottles for the operation of different equipment. Depending upon the maximum operating pressure of a given application and needs, air compressors may conduct two stages of compression, three, or more.

Valves are also crucial for controlling how gases traverse the system, and they can come in varying forms. Relief valves are implemented for the means of preventing structural damage, serving as pressure limiting units which reduce unsafe values. Control valves are also necessary for operations, featuring a three-port housing and other components that enable management over flow. Check valves are present within pneumatic and hydraulic systems, and such components take advantage of two ports and a spring mechanism in order to prevent backflow and force gases down a single direction.

Restrictors are considered a type of control valve that is common to pneumatic systems, and they will often feature two ports in which one is of a much smaller size. This results in a slowdown of airflow rate, reducing the speed of actuating units. Variable restrictors are a specialized type, featuring an adjustable needle valve which can turn to either increase or decrease the size of the opening. As air is forced through the inlet and out of the pressure port through the needle valve opening, the adjustment of the needle will determine airflow.

As present contaminates within a pneumatic system may cause damage over time or a failure, filters are regularly implemented to remove various unwanted substances. Featuring a two port housing, cartridge, and relief valve, air can be forced through the filter for the means of removing dirt with the cartridge. Standard screen filters are also common, utilizing a wire screen to prevent the flow of various undesirable substances.

Moisture is also detrimental to operations, and components such as a moisture separator or chemical drier may be used. The moisture separator will often be located near the compressor, charged with removing any liquids following the equipment piece. With a reservoir, dump valve, pressure switch, and check valve, moisture is removed while maintaining airflow and preventing backflow. Chemical driers, meanwhile, are placed in various locations of the pneumatic system in order to collect and absorb moisture with the use of a cartridge.


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October 5, 2021

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