Air Compressor Check Valve

Modern times find us with an increased use of machines, tools, and appliances in our daily life as well as in industries and factories. Automated machines, on one hand, have simplified our work for us. On the other hand, they need the necessary protection to save personnel and equipment from any hazard. Similarly, an air compressor comes equipped with a check valve to prevent any unwanted situation. Almost all compressors in market today have one or more check valves. Some types that use this valve are:

  • Scroll compressor
  • Reciprocating piston compressor
  • Rotary Screw compressor

Let us have a look at the air compressor check valve and its functioning.

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Check valve, non-return valve, one-way valve are all names of a single type of valve. As its name suggests, a check valve allows the flow of either a liquid or a gas in a specific direction. It blocks the reverse flow, also known as backward flow, which is highly undesirable, as it can result in contamination and malfunction. Thus, it is safe to say that the check valve on an air compressor lets air pass in one direction and prevents its backward flow.

Check valve lets a variety of media through, such as

  • Gases
  • Steam
  • Liquids
  • Condensate
  • Air

Its applications are wide ranging, such as

  • Pump and compressor discharge
  • Condensate lines
  • Cooling towers
  • Boilers
  • Injection lines
  • Steam lines
  • HVAC systems


One can simply observe the working of a check valve by blowing air through it. It will let the air pass through one side; however, it will block the air blown in from the other side. Similarly, once the compressed air leaves the nozzle of the check valve, it can’t return to the air compressor. The passage of air through the valve is in a single direction only. It helps the compressor to keep certain parts under and out of pressure. This valve simply functions like a swinging door; the higher the velocity or pressure of air, the more it opens and vice versa.

In a piston compressor, when the piston moves to the bottom, the air comes in the valve on the inlet nozzle via suction; then, the upward movement of the piston makes the compressed air flow out of the cylinder via the valve on the outlet nozzle. The minimum pressure required to open the valve is the cracking pressure.

An important query now arises. What happens if there is no check valve present on the inlet? Once the piston moves upward, air will try to move out through the inlet nozzle- a part of least resistance- without being compressed. Thus, the air compressor will fail to fulfill its required purpose. The check valve on the inlet ensures that the air inside doesn’t move back during compression process; while, that on the outlet ensures that the compressed air doesn’t flow back to mix with uncompressed one.

A check valve on an air compressor operates on the pressure of air. Its construction is such that an inside object, such as a disc, seat, stem, hinge, pin, spring, ball, cover etc. allows the forward flow of fluid and it closes the valve once the forward flow reduces or reverses.

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What part of an air compressor houses the check valve depends on the compressor’s type, mode, size, brand, etc.

The check valve on the compressor stops the air from bleeding out of the tank once it is full and the compressor power is off.

On reciprocating piston compressors, check valves are present in several places. For instance, a pair of check valves, located inside the piston head, controls the airflow to and from the cylinder.

One more check valve is present between the compressor and the compressed air receiver i.e. the air compressor tank. This valve ensures that once the compressed air is inside the tank, it does not flow outside.

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Port 1 shows the connection for the pump head. The compressed air flows into the tank from the pump.

Port 2 is the air line to the unloader valve. During the pumping of air from the compressor to the tank, this port is shut so that the air can’t escape to the atmosphere.

Port 3 shows the connection for the compressor tank. Compressed air enters the tank through this port.

A check valve has several threads, which fit snugly inside the neck of nozzles. These threads make it easy to mount or dismount a check valve on an air compressor.



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  1. Brass air safety valve with soft seat
  2. Brass air safety valve with hard seat
  3. Cast brass air check valve
  4. Brass in-tank check valve
  5. Variable Pressure relief valve
  6. Brass in-line with unloader port valve
  7. Load gentle continuous run unloader valve
  8. Brass unloader valve


After reading my article on air compressor check valve, you can easily guess that it is a simple and small yet important part of an air compressor. It is replaceable with ease. The check valve functions as a swinging door for the air. It doesn’t need automation and works reliably for a long time. However, you can always perform a check to know whether your air compressor check valve is in good condition. If there is any leakage through the unloader valve, after the compressor is shut, it indicates your air compressor check valve needs replacement. Always seek help from a professional before repairing such tools. I hope you found this article informative and worth sharing. Leave a word in the comment box below and don’t forget to share it with your friends.

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