Air check valves are spring loaded valves on the outlet side of the meter. Most Liquid Controls meter systems with an air eliminator also have an air check or a differential valve. Air eliminators and air check valves work in conjunction to stop the flow of product through the meter until the air is eliminated from the system. In order to do this, the air eliminator and the valve are piped together at installation.
Air check valves are normally closed, but when the pump starts and pushes product into the system, the valve spring will give way to the flow pressure. In order to keep the valve closed when air is being expelled from the air eliminator, the air from the air eliminator is routed through the piping to the back side of the valve spring. The combined force of the expelled air and the strength of the spring keep the valve closed until the air is eliminated.