What Are Bellows and How Are They Used in Aircraft

Bellows are a device that is designed to provide strong blasts of air  through the compression of the assembly. Aircraft bellows can come in a wide variety of types, allowing them to serve applications such as metallurgy, fluids transfer, aviation, and more. In regard to aviation, bellows can be used in a number of ways such as converting pressure and temperature into motion, assisting altimeter functionality, and transferring oil  through the engine for cooling. Due to the various roles that such components serve, it is useful to understand what they are and how they function.

Depending on the application that aircraft bellows will serve, they can be designed in a variety of ways and with different materials. It is common to use elastomer or thermoplastic coated fabric for the construction of the bellow frame, though manufacturers will take into account the various fluids, chemicals, temperatures, and other environmental factors that may affect the performance or health of aircraft bellows. For the types of elastomers that may be used for bellow construction, common materials include chloroprene, polyethylene terephthalate, Chlorosulphonated polyethylene, nitrile, Styrene-butadiene, ethylene propylene diene monomer, and silicone. For thermoplastics on the other hand, PVC and polyurethane are most often chosen.

Due to the role that bellows serve, it is important that they are regularly inspected and cleaned to ensure long service lives and optimal performance. When inspecting the bellow frame or other bellow components, one should clean them to remove any debris that may cause abrasions or other forms of damage. If bellows become damaged or fail, they should be replaced as soon as possible before conducting a flight operation.

When bellows are employed in pressure sensing application for the means of speed detection, such components are constructed from metal. Nickel serves as the most commonly used material, and the metal is leak-tight and electrodeposited. The nickel walls are also designed to be quite thin with a thickness of just 0.013 mm. This allows the bellows to remain sensitive so that they can efficiently respond to minute changes of pressure.

Bellows also often serve aircraft for communication devices as newer technologies require the careful management of signals when carrying out high-frequency connections. In such assemblies, the servometer bellow contacts are gold-plated, and they present high flexibility, reliability, and low dB losses which makes them quite efficient. Additionally, many aircraft communication designs may also take advantage of convoluted servometer electroforms which can flexibly perform as low-loss waveguides.

As stated before, bellows can be used for fluid applications, and many aircraft may feature them within the oil cooler flow control valve assembly. As oil is transferred through an engine, the bellows located within the flow control contact or other assemblies will actuate valves based on the temperature of oil. If the oil is cold, the bellow will lift a valve from its seat so that oil may flow around the jacket to warm. Once the oil has warmed up to its operating temperature, the bellows will expand so that the outlet is closed.

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1. craig lewis
2. Posted on April 19, 2021
aviation

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