Pressure Measurement & Control

Pressure switches with metal bellows

September 2021 Pressure Measurement & Control

What advantages do pressure switches with metal bellows offer and what is the basis for these? The advantages are based on the seamless design of the measuring system. This solution enables permanently stable repeatability and at the same time, eliminates the risk of leakage.

Bellows measuring systems are based on a mature manufacturing technology. The production of metal bellows, for example, from stainless steel or a copper alloy, takes place in several steps. Circular discs are first cut from a flat piece of metal and these are then shaped into cup-shaped objects. They are softened through an annealing process in a furnace at more than 600°C and then drawn into long, thin-walled and seamless tubes.

Constant elasticity

The tubes are corrugated by using forming tools at high pressure and then trimmed to the designed size. In the next stage, the spring-like metal cylinders are pressed together in accordance with the specified dimensions (length and outer and inner diameter). This creates the constant elasticity needed for the stable repeatability of movement. In the final step, the bellows are degreased and given a protective coating against corrosion.

Seal-free functionality and permanent accuracy

In a pressure switch, the metal bellows is brazed or welded to the process connection. Its other end is in contact with the transmission mechanism. This means that the instrument has a fully seamless measuring system without the need for any rubber sealing materials and the risk of leakage is eliminated. This feature makes pressure switches with metal bellows suitable for a wide range of applications. Process reliability is also guaranteed with liquid media.

A metal bellows changes its length in line with the pressure. When a defined switch point is reached, it triggers the switching function via a transmission mechanism. If the pressure drops or rises again, the bellows returns to its original shape and the switch contact returns to its original position.

The expansion movement of a metal bellows has a high linearity. The switch differential, which is precisely adjusted via a specific calibrated spring system, remains correspondingly constant. This ensures the accuracy of pressure control and switching, even over a long period of time.


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