Air check valve

Air Check Valves

Check valve

Figure 1: Check valve

An air check valve allows air to flow in one direction and prevents any flow in the reverse direction. Also called pneumatic check valves, they are widely used in air compressors and pneumatic and vacuum systems. Choosing the right check valve for the air compressor is crucial as any issue with the valve can directly affect the compressor’s performance. This article discusses the working of an air compressor, the role of an air check valve, and the various ways to maintain the valve and the compressor.

Table of contents

Air check valves

An air check valve allows airflow in the forward direction and prevents any backflow. The most common application of an air check valve is in an air compressor. Air check valves allow the compressor to keep certain parts pressurized and other parts de-pressurized. These valves can be located on a piston compressor (inlet and outlet), air receiver, or discharge pipes.

Air compressor

An air compressor is a device that takes air at atmospheric pressure and compresses it to a higher pressure. The compressed air is then stored in a tank for later use. Air is forced into a container and pressurized. The air is then let out through a tank opening, where the pressure builds up. Compressed air can be used as an energy source as it is released. For example, consider a hand-operated tire pump. Air enters the pump’s cylinder as the plunger is raised. The compressed air is forced into a bicycle tire or ball as the plunger is pushed down. Compressed air is used in a number of applications like:

  • Refrigeration cycle
  • Spray painting
  • Pumping water
  • Operating blast furnace
  • Operating air brakes in trucks, buses, and trains
Air compressor

Figure 2: Air compressor

Air compressor working

Air compressors consist of a piston that moves vertically inside a cylinder, compressing air in the cylinder. When the piston moves upwards, the volume of the gas decreases, and pressure increases. On the other hand, moving the piston downwards increases the gas volume and decreases the pressure. By compressing the air, the compressor increases the air pressure.

The compressor has inlet and outlet pipes. The air inlet is located at the bottom of the cylinder and opens as the piston moves up. The outlet is located at the top of the cylinder. The outlet opens when the piston moves down, allowing air to flow out of the cylinder.

Air compressor check valve

A check valve prevents the air from the pressure tank from going back into the piston cylinder. The check valve mechanism keeps the outlet sealed when there is a higher pressure on the outlet (tank) than on the compressor side. Without a check valve, there would be no way to fill the pressure tank.

Air compressor check valve issues

A check valve failure can damage the compressor in the following ways::

  • If the check valve remains stuck in its open position, it can allow air to leak back into the compressor when it is not running. This process damages the compressor by causing it to spin backward.
  • If the check valve remains stuck in its closed position, the air pressure increases uncontrollably, ultimately leading to a compressor surge. A compressor surge is a condition that occurs when the amount of gas being compressed is insufficient for the size of the compressor. Due to this, the device loses its ability to transfer energy from the compressor parts to the fluid, causing the reverse flow of air within the device.

Bad air compressor check valve symptoms

Understanding the symptoms of a bad air check valve will allow for proper troubleshooting to prevent future issues from occuring.

  • One of the common signs of a malfunctioning check valve is compressor surging. Due to this, the compressor shuts off immediately after it is switched on. This scenario occurs when the check valve does not prevent the backflow of air into the compressor.
  • The hissing sound produced when the compressor runs indicate a bad compressor check valve. The hissing sound may be an indication of air leaking from the tank. Air oozing out of the unloader valve when the compressor is shut off also indicates a malfunctioning check valve.
  • A check valve may leak if the valve seats are damaged or the disc is not properly seated. Debris accumulation in the seat may also cause leakage. Leaking compressor check valves often leads to significant wastage of compressed air. If you notice a leaking unloader valve, it is advisable to switch off the air compressor. Then, depending on the damage to the valve, repair or replace the valve.
  • It is vital to inspect the check valve regularly for any malfunctioning symptoms. If you notice symptoms indicating a malfunctioning check valve, it is advisable to attempt cleaning the valve. Below is a guideline on how to clean air compressor check valves.

Cleaning air compressor check valves

Perform the following steps to clean the check valve in an air compressor:

  1. Disconnect the airlines and remove them from the compressor tank.
  2. Blow air through the check valve in the opposite direction of normal flow. Clean the interior of the check valve with a cleaning solution. Flushing hot water through the check valve can also aid in cleaning. To remove dirt from the valve body, use a towel and a wire brush.
  3. Lubricate the check valve after it has been cleaned. Lubrication increases the efficiency of the valve and the check valve's lifespan.

Replacing tank check valve

  1. Turn off the compressor's power supply.
  2. Unscrew the check valve from the compressor carefully. Clean the area around the valve opening to remove dirt and excess debris before installing the new valve.
  3. Before replacing the air check valve, ensure that the specifications of the new valve match the compressor. Consider the fitting sizes and operation limits before replacing the valves. You may also modify the size to fit your need through bushings. Read our article on check valve installation for more information on how to install a check valve.

Air Injection check valves

Air injection systems are designed to reduce emissions by combustion engines. The air injection system works by injecting air into exhaust systems. The injected air oxidizes the exhaust gases, thus reducing carbon monoxide and hydrocarbon emissions. The injection system works together with a catalytic converter.

The air injection system comprises a pump, a controller, a set of injectors, and check valves. The pump supplies air to the injectors, and the controller controls air pressure. The injectors are responsible for injecting air into the exhaust system.

The air injection check valves are used to prevent the backflow of exhaust gases from the combustion engine into the injection system. Whenever the exhaust pressure exceeds the injection pressure, the check valve closes to stop the reverse flow of exhaust emissions.

Check valve selection

  1. Sizing: Choose an appropriately-sized check valve based on the valve’s orientation (horizontal or vertical) and media flow rate within the compressor.
  2. Filters: Install filters to keep the check valves and compressor lines free of debris.
  3. Materials: The materials chosen for compressor check valves must be compatible with air. Brass and stainless steel are commonly used to construct the check valve for air compressors.


What can I do to ensure my air check valve operates efficiently?

Inspecting the valve regularly for wear and damage can help ensure that the valve is working correctly. Testing the valve regularly can also ensure the valve is functioning properly.

What is the purpose of air check valves?

The purpose of air check valves is to prevent the reverse flow of gas piping systems. This is accomplished by allowing air to flow in only one direction.

What risks are associated with air check valves?

Failure of the valve to close properly and leakages are the common risks associated with air check valves. These risks can lead to wastage of energy and reduced efficiency.