How to test the Check Valve on the Compressor Tank

An air compressor has many accessories that ensure its smooth and efficient operation. One such feature is a check valve. As its name suggests, the check valves maintains a check or restriction on the backward flow of air from the tank to the pump. That means, in an air compressor, air flows from pump to tank and not the other way round. The check valve ensures that the air follows this mechanism.

You should ask yourself questions like why it is necessary to test a check valve or even replace it. What conditions point towards a faulty check valve?

In case of failure of the check valve, the motor will not start. The reason is that the air flows backward from the tank to the pump and exerts pressure on the pump head. Thus, motor doesn’t start on a full tank and runs on an empty one. This condition is undesirable. Hence, in order to ensure the proper working of the motor and ultimately the compressor unit, you need to replace the faulty check valve.

In order to avoid the replacement process, you can also perform a maintenance check on the check valve.

The main location of the check valve is the air tank; it is threaded into the tank containing pressurized air. These threads are snugly tightened in form of a reddish pipe on the tank itself.

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In the above figure, there are three ports shown labeled as 1, 2 and 3.

Port 1: It shows the point where the connection from the pump has to be made. The line that brings compressed air from the pump links to the port 1 of the check valve. This air then flows into the tank.

Port 2: On this point, the connection of the airline is made. This airline is joined to the unloader valve. This unloader valve is on the side of the pressure switch of the compressor or there is an internal unloader inside the compressor. The main purpose of the unloader valve is to prevent the air from escaping to the atmosphere. When the pressurized air comes towards the tank from the pump via port 1, the unloader valve is in off position so that the air remains trapped inside and finds no way out.

Port 3: At this point, the check valve comes in contact with the compressor tank. The air coming from the pump crosses the check valve and enters the tank via port 3. The flapper valve, which is basically the actual or main check valve is located in this part of the check valve.


In the case, when the flapper valve encounters a problem like a breakage or leak, air will escape via port 2 from the tank. You can easily detect this fault using your naked eye. When you stop the compressor and even after unloading the pump, the leakage of air continues. This leak is through the unloader valve.

Now don’t wonder where is that air coming from. In the case, when you have shut off the pump, air can only come from one place. That is the compressor tank. You are losing pressurized air that you had gained on the expense of electricity and ultimately money. Thus, you can’t afford such a fault in your compressor unit. So it’s time you detect and fix this problem.

Don’t worry! Testing the check valve involves no rocket science. It is simple enough and you will know it just like you know the back of your hand. In this guide, I bring you a simplified method that will help you on how to test the check Valve on the compressor tank.


  • Take a rag cloth and cleanse the shank or surface of the check valve on the tank valve thoroughly. Make sure you also clean the tank threads. Be sure as not to leave any surface unclean, as you have to put your mouth on that place. When no dust remains, place your lips in such a way around the valve that you can blow through it. Your mouth is on a point under the threads.
  • Place a finger on the other two ports, i.e. port 1 and 2.
  • When you will blow, two things will happen; either the air will leak or it will not leak.
  • If there is a fault in the flapper valve, air is sure to leak from the other two ports and your fingers will feel it.
  • This air is leaking through the unloader valve. You can say the check valve in this case is not seating.
  • May be this leak is due to the presence of dirt or unsettled check valve. So rinse it in a hot water tub or soapy water. Don’t use it again until it is thoroughly dry. Then, replace it back on the tank and test it again through the same process. If the air still exits, then you have to replace the check valve. I have discussed the procedure of replacing the check valve in one of my other blogs. Take help from there and you can easily get your compressor unit running like a new one in short time.


Replacing the check valve is no rocket science. I hope you found this blog useful because of its simplicity and comprehensiveness. You don’t have to call a plumber for such a small repair task. You can DIY. Do not forget to share it with other so that they can also benefit from this information. Leave comments in the section below.

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