Bellows For Pressure Sensing

One of the most common uses for metal bellows is in pressure sensing devices, including all kinds of industrial pressure gauges and switches.  Watch our latest video to learn why bellows work so well in pressure sensing applications. 

 




Maximize Aneroid Performance

Altitude-sensing aneroids play a crucial role in flight systems. But keep in mind that the aneroid will only be as good as the metal bellows or diaphragm capsule that serves as the pressure sensing element. Here's a brief introduction to what you need to know about aneroid performance.

 




New 2-Pin Deutsch Pressure Switch For Tough Environments

Our 784 Series of ruggedized pressure switches can now address more applications than ever, thanks to the addition of a compact 2-pin Deutsch option. Other than the change in connector, the pressure switch offers all the same performance characteristics as the original 3-pin Deutsch version.

IP67-Compliant Pressure Switch. Whether 2- or 3-pin, the 784 pressure switch complies with IP67 standards for maximum environmental protection. This model thrives in tough environments containing oil, fuel, water, dust, vibration or shock.

 

784 2-Pin Deutsch

With a temperature range from -40 to 250°F, the 784 pressure switch comes with a piston, fixed pressure, integral pressure port snubbing and an 8 to 6,000 psig range. Some common applications include:

  • Off-road equipment
  • Industrial OEM equipment
  • Train braking systems
  • Packaging equipment
  • Compactors
  • Compressors

Other Features. This customizable pressure switch also features a snap-action electrical switch tested to one million cycles, gold contact switches for dry circuit applications, high overpressure capabilities and custom configurations. In addition, this model meets UL safety standards and NEMA type 4 outdoor applications and instances where water is present.

You can learn more about our design approach to ruggedized sensors in our latest white paper.

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Understanding Metal Bellows Manufacturing Methods

You can’t begin to talk about metal bellows performance without considering manufacturing methods. All key performance parameters depend on the way the bellows is formed or welded. Let’s take a look at two of the most common manufacturing methods: seamless hydroformed bellows and seam-welded formed bellows.

Seamless hydroformed bellows. As their name suggests, seamless metal bellows have no welded joints. Instead, they’re produced in a multi-step deep drawing process. A secondary hydroforming step forms the convolutions. The deep drawing and hydroforming processes can hold consistent dimensional tolerances. For example, wall thickness variation from a well-controlled deep drawing process is within ± 0.0001 inches.

In high-volume applications requiring a small package size and a precise spring rate, seamless bellows are by far the most popular choice. These applications include many kinds of appliance, HVAC and industrial controls and sensors.



Hydroformed Seamless Bellows

Seamless bellows do have some package size limitations. Their sweet spot for OD lies between 0.25 and 3 inches. Seamless bellows also have a higher initial tooling cost than seam-welded bellows. At production volumes, however, the tooling costs of bellows all but disappear.

Seam-welded formed bellows. Made from rolled, welded and formed sheet metal stock, seam-welding excels at producing large diameter bellows cost effectively. Diameters up to eight inches are not uncommon and would be cost prohibitive with seamless deep draw production methods. Seam-welded bellows can also be fabricated to any required length. And they have low initial tooling costs.

So seam-welded bellows are perfect for applications that need a large, cost-effective bellows, such as expansion joints or other connections that compensate for the movement of mating components.

Seam-welding bellows, however, do not lend themselves to applications that require a very precise spring rate. The reason is that their wall thickness tolerances are determined by the sheet metal stock, not the precision deep drawing process. Typical wall thickness variation for seam-welded models is ± 0.0005 inches, or about five times greater than a seamless bellows.

With wall thickness tolerances influencing spring rate and mean effective area, seam-welded bellows inherently have a less precise response to pressure and applied forces, which rules out many sensing and control applications.

 

Check out our white paper

 

 


Video: Ruggedized Switches Withstand Pressure Spikes

Ruggedized pressure switches have a stable switching response and a long lifecycle in the face of temperature extremes, moisture, chemicals, vibration, shock and pressure spikes—the biggest threat of all. Our high quality switches have a number of design features that help withstand these spikes. Check out this video now.

 

 




How To Make Pressure Switches That Last

Simple design principles for harsh operating conditions

Ruggedized pressure switches play a critical role in failure-intolerant applications. At Sigma-Netics, we define rugged as a stable switching response and long lifecycle in the face of seven failure modes—pressure spikes, leaks, temperature extremes, moisture, chemical exposure, vibration and shock loads.

Switches that can withstand these life-ending failure modes have three design principles in common. They tend to have a piston rather than diaphragm design. They have carefully designed pressure management features and seals. And they use materials and construction methods that mitigate chemical and moisture exposures, as well as thermal expansion mismatches.

Pressure Switch White Paper

In our latest white paper, we'll take a closer look at some design principles of ruggedized pressure switches.

 

Download the white paper

 

 


Designing With Metal Bellows

Metal bellows have long been a key component in demanding sensing and sealing applications. In fact, they’ve become so familiar that many engineers now think of bellows as generic items: Just specify a few key dimensions, pick a metal alloy and you’re good to go.

The reality, however, is that not all bellows technologies are created equal. Different manufacturing methods and material grades can have profound effects on how metal bellows will perform in terms of their stroke, pressure capabilities, 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 your expected lifecycle.

Designing with Metal Bellows White Paper

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 your expected lifecycle.

Our latest white paper takes a close look at the different aspects of metal bellows–including design considerations, manufacturing methods and materials–to help you pick the right one for your application.