Differential/Air Check valves are placed on the outlet side of a metering system and work in conjunction with the system’s air/vapor eliminator to stop the product flow through the meter until the air/vapor is eliminated. To do this, the air/vapor eliminator and the valve are connected by a copper tubing at factory.
Differential/Air Check valves are normally closed, but when the pump starts up and pushes the product into the system, the valve spring will give way to the flow pressure. In order to keep the valve closed when air/vapor is present and the float drops down drawing its reeds and opening the air eliminator vents, the air/vapor from one vent goes to the vapor recovery line whereas from the other vent it moves through the above said tubing to press down the differential/air check valve. The combined pressure of air/vapor and valve spring keeps the valve stopped until the air/vapor is eliminated.