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While not essential for using your air compressor, it’s always useful to know a bit about air compressor gauges.
The vast majority of DIY, workshop and small plant air compressors will have two air gauges.
One of them displays the compressed air pressure that is the tank at that time. If you can see how the air gauge is mounted, the tank air gauge is always plumbed directly to the tank.
It is the tank air pressure gauge, a typical one of which is shown below, that fluctuates all the time as air is being pumped into the tank by the compressor pump, and as compressed air is being used. The tank air gauge can be back mounted as is the one in the image below, or it can have a mounting nipple on the bottom. Both styles are relatively inexpensive at $6-$10 or so, both styles have pressure ranges from 0-160 PSI or perhaps zero to 200 PSI depending on the brand, and the choice between the two mounting styles is made based on how the gauge is attached to the compressor.
If your current tank air gauge has a pressure range of 0-160 PSI for example, and you need to replace it, feel free to replace it with one that has a pressure range of 0-200 PSI should that be the only gauge available. These are dumb devices, and as long as the pressure range of the gauge you select is equal to or greater than the upper pressure range of your compressor pump, you are good to go.
The thing about air compressor gauges is that eventually tey do rust out. They do break. If that happens, replace the gauge immediately as you do want to know what’s happening, air pressure wise, inside the tank.
It is the tank air gauge that displays the air compressor cut in and cut out pressures, and will tell you very quickly, if you know what these pressure settings are when the pressure switch is operating properly, if the switch settings are changing. This indicates a problem with your pressure switch.
Regulator Air Gauge
The other air gauge on a typical air compressor is the one that is plumbed to the air compressor regulator.
This is an important gauge as it displays the pressure setting of the regulator. Your tank gauge may show 150 PSI when the tank is full, yet the pressure gauge may display only 80 PSI, or whatever the pressure setting is on that air regulator.
On your air compressor, your air regulator gauge may be plumbed directly onto the air regulator, as is the one in the image above, or it may be installed in a panel with the air line to the regulator plumbed from behind.
By turning the air regulator knob in one direction you increase the pressure setting and in the other, decrease it. Regardless of what way you turn the regulator knob, the air pressure regulator gauge will display that setting.
There is one time it will not, however. A regulator can only regulate pressure that is higher than the setting. If, for example, you turn the knob to increase the downstream pressure, and say for example your tank has 100 PSI in it, as you turn the knob on the regulator to increase the pressure setting, you will see the gauge needle indicate a higher pressure setting, but only until the regulator setting reaches 100 PSI – the pressure in the tank. Even if you continue turning the regulator knob to dial up a higher pressure, the display on the gauge will only go as high as the pressure that is available in the tank.
If you want your regulator gauge to register a higher pressure than 100 PSI, then you have to have more than 100 PSI in the tank.
About Air Compressor Gauges
Both the tank air pressure gauge and the regulator gauge can be the same size (typically 1 1/2″ in face diameter) and with the same mounting thread (typically 1/8″ NPT) regardless if the mounting is bottom or back. They can also display the same or different pressure ranges depending on the ranges you want available.
In the smaller, DIY type, air compressors, you frequently see the tank gauge being 1 1/2″ in diameter and a 1″ diameter regulator gauge.
Again, regardless of the size, both air compressor gauges display the pressure that is flowing through the mounting hole to the sensor inside, and as long as a new pressure gauge that you may acquire fits the mount, fits for the diameter, and has the same pressure range as the original, feel free to use any gauge you can acquire.