Presair Switches Can Sense Pressure or Vacuum

What’s the Difference Between a Pressure and Vacuum?


Pressure and vacuum switches can look exactly the same. Yet, the systems they’re used in can differ greatly. So what’s the difference?

It’s quite simple in reality. Presair makes switches that can be used to sense either a pressure or a vacuum. These switches have a rubber diaphragm inside and two different air ports. The air ports are located on opposite sides of the diaphragm, one above and one below. In order to actuate the switch, the diaphragm needs to be pushed against the switching mechanism.

So in a pressure switch, air pushes against the diaphragm until it makes contact and completes the electrical circuit. This actuates the switch. Notice the picture below:

Vacuum App2

For a vacuum switch, the same motion occurs. Only instead of air pushing the diaphragm, it’s pulling the diaphragm from the other air port. It requires the same amount of force to actuate the switch whether it’s vacuum or pressure. Notice the picture below:

Vacuum App1

So it all comes down to this. Air is either pushing the diaphragm up, or sucking it up. That is the difference between a pressure switch and vacuum switch.

Pressure Example: An example of a pressure application would be monitoring the amount of fluid in a tank. As the tank fills up, there is less room for air in the tank which creates more pressure. Once the desired amount of pressure pushes against the diaphragm, the switch actuates to turn something on or off accordingly.

Vacuum Example: An example of a vacuum application would be lifting a sheet of glass with suction. In order to move sheets of glass, air suction is utilized to lift and place. A vacuum switch could monitor the amount of suction force and notify accordingly as it rises or falls.

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