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.
i have a husky c331h 33 gallon air compressor, what should my two gauges be set at?
My tank is a 29 GALLON w/ max 150psi. Last couple times I’ve used it the tank gauge stays at zero while filling up after I turned it on. I seem to get plenty of pressure and use my tools with normal performance. The release valve when pulled let’s out what seems like normal release pressure. Is this a bad gauge or is something else wrong. Two uses ago it filled up and the gauge seemed to go near 200 but as mentioned above is now at zero
hi my air compressor tank gauge reads good, but the regulator gauge goes upto 50 psi. Why can’t i adjust it higher for the tools. my tank pressure is 200 psi. I rebuild the regualator, thank you for your help Ron.
I have my regulator set at 150 but when I activate my air chuck the regulated air gauge moves down? Solutions?
My comp nail gun says no more than a hundred psi what do I set the tank Gage to
On my 100 psi compressor, The manifold holding the gauges and pressure regulator broke and is no longer manufactured. Is there any problem if I construct one from regular brass plumbing fittings?
How is the compressor cooled?
Just got a little 2gal anvil air compressor. The tank gauge shows AN increase in psi, but the outlet gauge does not show any increase. There is no air traveling through the hose into the apparatus that is attached. Please help me! I just bought this air compressor, and am doing everything listed on the instructions to no avail!
I have porter cable 150 2.5 hotdogs, never been used. Fills up fine and reads 150 on left regulator. Right reads nothing and no air releases from new hose or adaptors. An suggestions
Thank you for taking the time to answer my question everything you said makes perfect sense once again thank you Steve
Steve, if the compressor has two coupler outlets, one from the regulator and the other with tank direct feed, if you use the latter, whatever pressure is in the tank is what the air tool will get. Far better to use the coupler from the regulator so you can dial down the pressure to the minimum operating pressure for the air tool, reducing wear and tear on the tool, and extending the compressor life by reducing the frequency of the cycle time.
Do I plug my hose in the regulated air or the unregulated are both have a connection
The gauge that moves when you rotate the knob on the regulator is the gauge that identifies the air pressure going to the air tool. The other gauge identifies the pressure in the tank.
What gauge is telling me how much air is being provided to my tool? Tank or Reg.?
OK then, that strongly suggests that the diaphragm inside the regulator has cracked. Yup, I would say it’s time for a new regulator. Good luck, and maybe let us know if that resolved the issue?
No I have never had it off and rarely use it. It’s about 20 years old so I thought I should buy a new regulator.
To question 1 Mike, yes, if the tank is low in pressure, as the tank pressure rises from the air flowing into the tank, both gauges will register this increase in pressure at the same time. However, the regulator gauge needle should stop at the pressure setting that the regulator is set to, while the tank gauge will continue to register increasing pressure until the compressor stops. And 2, no, if you turn the adjusting knob on the regulator the regulator gauge needle should move in accordance to the setting as the knob is turned. That is, assuming that the… Read more »
When I start my craftsman air compressor both the regulator gauge and tank guage both climb at the same level of pressure. Question 1. Is that normal? And when I turn the regulator knob either direction the regulator guage doesn’t move. Question 2. Is that normal/correct? Thanks. Mike
Hi Betty. I’m a bit confused by your question. Maybe you can help me? By the output gauge, are you referring to the tank pressure gauge? And by the pneumatic diverter, is this, perhaps, the gauge on the regulator? If so, the tank pressure gauge displays the pressure you have available in the tank. The regulator gauge displays the pressure that the air tools downstream from the regulator will receive. In other words, the regulator will “regulate” the pressure to the air tools to 30 PSI, regardless of the pressure in the compressor tank, and for as long as the… Read more »
If a compressor output is gauge is reading 100psi and the pneumatic diverter is reading 30psi for its incoming pressure, what is the problem?
You can use any gauge with any pressure switch that you can thread in and that has similar (if not identical) pressure ranges. The tank pressure gauge has no control over the pressure in the compressor tank. It simply displays what that is. The pressure switch cut in and cut out settings operate the compressor. The thing I don’t understand is, if you move the regulator gauge to the tank gauge spot, what gauge will you use to identify your pressure setting for the air stream from the regulator to your air tool. I think I’m missing something here. Maybe… Read more »
Can I use only a regulator gauge in my craftsman 5 HP compressor with the same pressure switch. My original dual gauge set up started leaking. Thanks for the help
The air tank gauge displays the pressure in the tank. The only way to adjust that is to change the settings on the compressor pressure switch. I don’t recommend doing that. If you are talking about using the air regulator to reduce the pressure flowing to your spray gun, then by all means, do do. That’s exactly what the regulator is for. As you adjust the regulator, the tank gauge should not change. The gauge on the regulator will reflect the new pressure setting.
I have just bought a cobra 50 LTR compressor. Should I adjust the preset outlet pressure setting on the air tank or should this not be messed with?
I am spraying paint so only need 2 bar.