F Series excess flow valves are intended to close upon excessive discharge of vapor or liquid resulting from a break in the hose or piping system. They are used to protect cylinder, tank and piping systems, and are available in a large variety of sizes and body configurations. When flow exceeds the valve?s setting, the valve closes and remains closed until the system equalizes. A built-in equalizing passage automatically opens the valve once pressure on both sides of the poppet is equal.