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Understanding Differential Pressure Switches

Differential pressure switches can seem difficult to understand at first. To the layperson, their name doesn’t immediately indicate what they are or what they do. The average person might have heard what a pressure switch is and does; it’s a metering and control utility that can control the flow of something and in some cases provide a meter reading as well. But knowing the difference between that and a differential pressure switch requires some specific knowledge. What is differential pressure, anyway?

For the engineers in the audience, go grab a snack or something and come back in a few paragraphs; this will be remedial for you. Differential pressure is actually a very easy concept to grasp. It is the difference in pressure between two objects. For example, if I have a vacuum flask that is depressurized so that it has an internal pressure reading of X, and if I also have another vacuum flask with an internal pressure of X + 5, then my pressure differential is five. See? Easy.

Now that the engineers have returned from retrieving their snacks, we can all come together and talk about why differential pressure gauges are important. Engineers involved in studying fluid dynamics probably already know why differential pressure switches are important. However, having been steeped in conversations about fluid dynamics and classical physics, they may not have found room for some of the more imaginative uses for differential pressure switches. One of my favorite examples is the example of the kind of airlock pressurization system found in spacecraft and space stations. During extra-vehicular activities, astronauts have to pass through a pressurization chamber that acts as a buffer between the pressurized interior of the spacecraft and the near-vacuum of space. Differential pressure switches are used to help adequately re-pressurize these chambers when astronauts return from their EVAs. Of course there are many less exotic uses for differential pressure switches, but it’s helpful to remember that even seemingly uninteresting equipment can be used for very interesting purposes.