Good question. Why does the air compressor have two gauges?
We are speaking, of course, about the little round displays that appear on most air compressors. These are shown in the image below, pointed out by the white triangles.
The faces of these gauges will show a range of pressure, usually from 0 PSI up to around 150 PSI. Don’t be alarmed if your pressure ranges are a bit different, as each gauge suits the compressor on which it is installed. The pressure range displayed on your gauges might be 0 PSI to 100 PSI, or 0 to 250 PSI, or any other range, all depending on the pressure capabilities of that particular air compressor.
In the image of the two gauges, on this portable Porter Cable air compressor, the air gauge on the left is the one that is displaying the pressure setting on the air regulator, and the gauge on the right is displaying the pressure level inside the air tank.
Regulator Air Gauge
You will want to have a look at the page on this site about air regulators to better understand what they do. In short, the regulator is used to reduce the available tank pressure to the best operating pressure of the air tool or air using equipment.
As you turn the knob on the air regulator, the pressure display on the regulator air gauge will change too and indicate the pressure setting that the downstream air will receive.
Tank Air Gauge
The tank air gauge displays the pressure that is inside the air tank. It is generally plumbed onto a nipple inserted into the tank so the air has an unimpeded flow to the gauge, although that’s not always the case. Regardless, air from the tank is exerting pressure inside the tank air gauge all the time and the face shows the actual pressure inside the tank.
If your air compressor has a cut in setting of 80 PSI for example, the tank air gauge needle will show a pressure drop as you use the compressed air from the tank, and when the tank gauge needle reaches the 80 PSI point, you should hear the air compressor start.
Immediately then, the needle on the tank air gauge will start to rotate indicating pressure is building in the tank. When the tank air gauge display reaches the cut out pressure, let’s use 110 PSI as an example, the gauge will show 110 PSI on the face, and your compressor should stop.
Tank Air Gauge Does Not Control Compressor Start & Stop
Neither the tank air gauge or the regulator air gauge have anything to do with starting and stopping your air compressor.
These two gauges display pressure readings. That is all.
It’s the compressor pressure switch that turns the air compressor on and off depending on the switch settings. It is the regulator that controls the pressure flow to your air tool.
If you have a question about your compressor air gauges, please feel free to ask it using the comment form below, and we’ll see if we can help.