So it seems like the air compressor has been running for far too long. You watch it for a while, then realize that something is wrong. The air compressor will not shut off! After all, most air compressors turn off automatically.
Is this a problem with your air compressor? If your air compressor will not shut off, this is a serious issue that should be addressed before using the unit again. Read on… for the reasons why an air compressor will not shut off and remedies for that problem follow.
My air compressor will not shut off! What on earth is the problem? There are a number of scenarios that come to mind that might cause this compressor problem and they are explained fully below.
1. Issues With The Cut Out Pressure Level
The cut out pressure level is the pressure level above which the compressor will stop producing compressed air. The cut out pressure is basically used to indicate when the tank is full and ready to use. Once the pressure in the tank reaches the cut out pressure setting level, this indicates that the tank is pretty much full and ready to use.
Once there is a decrease in the pressure level, the compressor will start pumping air back into the tank. In some instances, however, there may be issues. Sometimes, the air compressor continues filling the tank after the cut off level is passed.
Let’s talk about these issues in more detail:
Tank Pressure Does Not Reach Cut Off: One of the issues, when an air compressor will not shut off, is that the tank pressure (displayed on the tank pressure gauge) never reaches the cut out setting to allow the pressure switch to trip to off which normally results in the pressure switch cutting power to the compressor motor and the air compressor shuts off.
Tank Pressure Stops Building: On other compressors, the tank pressure might reach a certain pressure level – also displayed on the tank gauge – and then the pressure in the tank stops building. The result? Again, the tank pressure never reaches the air compressor cut out pressure setting and the compressor cannot shut off.
Pressure Exceeds Cut Off: A third scenario is when the compressor runs, the tank pressure rises, then passes the normal cut out setting, and the compressor continues to run until the pressure relief valve (PVR) cracks open to vent the pressure. Normally, the PVR should balance the pressure inside the tank by releasing some of the pressure to the atmosphere. However, in some cases, the pressure is too much for the PVR to handle. Otherwise, it still doesn’t solve the problem if the PVR is working and balancing the pressure while the compressor is just increasing the pressure exponentially.
Here are some other issues normally involved when an air compressor will not shut off.
2. Issues With The Pressure Relief Valve
As we stated above, the pressure relief valve (PVR) is used to maintain just enough pressure inside the compressor tank. It does this by balancing the pressure inside the tank. In other words, it acts as an equalizer. This is why many people call it the safety back up of the air compressor.
Because of this, if there is ever a case where the PVR is activated and the pressure in the tank exceeds the cut out pressure, the PVR should let off excess pressure by opening a safety relief valve or vent called the pressure relief valve.
Of course, this only happens when the cut out pressure setting level fails to stop the compressor from working. If the PVR fails as well, you could have a serious issue.
If this ever happens, it’s important that you do not use the unit until you get a replacement and repair the device. PRVs are easy to find. This Control Devices ST Series Brass ASME Safety Valve, 125 psi Set Pressure, 1/4″ Male NPT is a good example.
Pressure Relief Valves Available On Amazon
3. Issues With The Pressure Switch
The pressure switch is very important because it turns off the air compressor whenever the tank pressure is high and reaches the cut out pressure setting level.
Because of this, you should try to be familiar with the PSI of your compressor. For example, the most common range is between 100 to 175 PSI. Once you know your PSI setting, you will know when it is exceeded as the pressure increases in the tank.
If you ever find that the pressure switch is not working, it’s important that you replace it. If your unit is still under warranty, then you should surely get it fixed by the manufacturer.
Otherwise,e you will need to source it yourself. If you cant find one that fits at your local store, you may be lucky enough to find one on Amazon. The Secbolt 90-120PSI Air Compressor Pressure Control Switch with Pressure Regulator Gauges Safety Valve Fittings Set is a quick example for those looking for switches within the 90 to 120 PSI range.
Pressure Release Switches Available On Amazon
New H/D Pressure switch for air compressor 95-125 w/Unloader
4. Air Compressor Will Not Shut Off – Is Gauge Broken?
The next thing to do is watch the tank pressure gauge as the compressor is running.
So, the gauge should rise steadily to the normal cut out pressure setting of the particular compressor. So how do you fix this air compressor not shutting off problem when the gauge is causing it?
If the tank gauge does not rise at all, that may be a symptom of a failed gauge, though this is unlikely. Still, if the regulator gauge works, swap it with the tank gauge, with the tank empty and the power off to the compressor.
After swapping, start the compressor again. If once again the tank gauge doesn’t move at all, then it’s likely not the gauge that is the problem, it is that the pump is not delivering air to the tank, and the tank pressure level cannot increase to cut out as a result. If however, you find that you have a guage problem, you can get a cheap one on Amazon, for example, this one is good value.
Air Compressor Gauges Available On Amazon
5. Next, Check To See If Compressor Pump Is Actually Pumping
If the tank gauge is not moving at all, and the compressor motor is running, can you tell if the pump is pumping?
If the compressor hasn’t been running long enough for the pump to get too hot, or if it has, turn the compressor off and wait for it to cool, and then, resting a hand lightly on the top of the pump while the compressor motor is running should indicate if the pump is running and it’s not just the compressor motor running ineffectively.
If the pump isn’t running, then check any belts that connect the motor to the pump, or, if the compressor is direct drive, ensure that the coupling to the pump drive is still secure. If not, tighten it or tighten the belt if belt driven. Test again. If the pump still will not run it is likely that it has undergone a serious mechanical failure, and it’s time to take it apart to see what’s what.
More on this farther along. If you choose to replace it, there are several cheap portable options on Amazon,
More on this farther along. If you choose to replace it, there are several cheap portable options on Amazon, like this one;
6. Tank Pressure Rises And Stops Before Cut Out Pressure Level
If the tank pressure rises and stops before it reaches the normal cut out pressure setting, yet the compressor motor and pump keeps running, that is a strong indicator that the pump itself may have a problem.
Pull the pump air intake filter and be sure that air is being pulled into the intake, and that air is not blowing back out. If air is escaping there, you’ll need to open the pump up and replace the intake valve.
Pull the line that runs from the pump to the tank and try, with a gloved finger, to try and stop the air flow out of the pump while it is running. If you can do this, odds are good that it’s the high-pressure valve that has a problem. Again, it will be necessary to take the pump apart to check.
If the compressor is oil lubed, and a lot of air is blowing out of the oil fill tube, that points to badly worn piston seals, and yes, you will need to disassemble the pump to effect repairs.
7. Compressor Does Not Stop And PRV Opens
If the pressure in the tank reaches the normal cut out setting and the compressor motor does not stop, then the pressure in the tank will continue to rise until the pressure relief valve lets go, venting the over pressure, and defusing a dangerous situation.
If this is happening with your air compressor, you should not use it again until the problem is corrected.
The fix is, typically, a replacement pressure switch. The pressure switch is supposed to cut power to the compressor motor when the cut out pressure setting is reached. That the air compressor will not shut off then, yet continues to run and the pressure in the tank continues to rise, indicates that the pressure switch has not tripped to off.
There is a diaphragm in the switch that may have failed, or, perhaps the points in the switch have fused, the latter often being caused by a short in the compressor wiring.
Regardless, if the compressor reaches a pressure level that blows the PRV, get the pressure switch looked at, fast. Preferably before you use the compressor again.
Is It Dangerous If My Air Compressor Will Not Shut Off?
If your compressor won’t shut off, you are flirting with a very dangerous situation. The compressor will keep compressing air into the tank until:
a) It can’t compress any more because there’s more pressure in the tank than the compressor head can overcome
b) The pressure relief valve opens to safely vent tank overpressure
c) Neither of the two above happens, and your compressor tank undergoes catastrophic failure, with significant risk to all and sundry around
We hope that the PRV works.
Regardless, if the compressor won’t shut off, you need a new pressure switch RIGHT NOW. Don’t delay. Your compressor is in trouble, and so could you be if you don’t replace the switch.
Conclusion On Why Your Air Compressor Will Not Shut Off
As discussed, there are several, but two main scenarios that should come to mind as to why an air compressor will not shut off.
One is that the pressure switch has failed, the air pressure in the compressor tank bypasses the normal cut out point of the compressor, the pressure continues to build, and eventually, (we hope) the PRV lets go to prevent over pressurization. This points to the pressure switch as the problem, and it should be replaced soonest!
The other scenario when the air compressor will not shut off is that the pressure in the tank reaches a pressure level below the normal cut out pressure level, and the pressure in the tank will go no further. Since the pressure in the tank stops rising, it never reaches the cut out pressure setting, and the pressure switch cannot react to the set point and shut the compressor off.
Finally On Air Compressors Which Keep Going
Sometimes, especially old compressors will need some extra force to the switch to turn it off. However, in some cases, there is an actual problem with the pumping g of air to the compressor tank or a similar issue that should clause a serious alarm. This problem should be addressed as quickly as possible using the methods outlined above.
It’s important to remember that even if you have a working air compressor, improper handling, age, and improper maintenance can cause serious issues like this.
So, over to you. These are the main scenarios why air compressors will not shut off. If these don’t help, feel free to leave a question below.