How do I choose a bellows?

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Metal bellows have long been a key component in demanding sensing and sealing applications. In fact, due to their ubiquity, many engineers now consider them generic items&#;just specify a few key dimensions, pick a metal alloy, and you are good to go. Think of bellows as a combination of a piston and a spring. Like a piston, bellows can convert changes in their internal or external pressure into an applied force. Like a spring, bellows deflect elastically in response to an applied force and exert a reactive force.

The reality, however, is that not all bellows technologies are created equal. Different manufacturing methods and material grades can profoundly affect how metal bellows will perform in terms of their stroke, pressure capabilities, and spring rate and temperature response. Manufacturing methods and materials will also determine how long your bellows will last in the field. The wrong bellows may work for a short time but not achieve the expected lifecycle.

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To be successful with metal bellows, first gain an understanding of the basic design and sizing inputs. Bellows have some specification requirements that you probably did not cover in engineering school. Next, pay close attention to the distinction between different welded and seamless constructions. Each type strikes a different balance between cost and performance, and each has its own application sweet spots. Finally, consider the type of materials. Sometimes the choice of bellows materials will be obvious. However, it is more likely that you will be confronted with choices between different metal alloys, any one of which could meet your requirements.

Here is a closer look at what you need to know to pick the right type of bellows for your application.

Design Considerations

Bellows are a versatile component, having the characteristics of both a piston and spring. They are used in dozens of different sensing, fluid handling, and actuation applications. In general, these applications fall into four broad categories&#;sealing, temperature, evacuation, and pressure, otherwise referred to as &#;STEP.&#;

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