Excess flow check 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. Valves larger than 1/2” NPT
have a drill size No. 60. Valves with a 1/2” NPT and smaller
have a limited bypass to comply with NFPA 58.
WARNING: A break or leak downstream of an excess
flow valve that does not allow a flow equal to the valve
flow rating will not actuate the valve and could cause a
hazardous condition. For this reason, system operators
should be familiar with the shutoff valves in the system so
that necessary precautions can be taken in an emergency.
Care must be taken to be sure the valve’s closing rate
is less than the capacity of the LP-Gas or NH3 system in
which the valve is installed. Brass valves are not suitable
for NH3 applications.
See the WARNING on page 25, if these excess flow valves
are to be used on DOT Cargo Tanks..