Per 49 CFR 192.383 & AGA Guidelines
Understand EFV operating principles, 49 CFR 192.383 requirements, sizing methodology, and installation best practices
An excess flow valve automatically closes when gas flow exceeds a preset trip rate, protecting against uncontrolled gas release from a severed service line. Per 49 CFR 192.383, EFVs are required on new and replaced service lines serving single-family residences where operationally feasible.
The EFV trip flow rate must exceed the total connected appliance load flow rate multiplied by a safety factor (typically 1.4-2.0), while not exceeding the pipe's maximum capacity. This ensures the valve does not trip during normal peak demand but closes during a line break.
The bypass flow rate is the small amount of gas that continues to flow through the EFV after it has tripped closed. This controlled leakage allows the valve to automatically reset when the downstream pressure equalizes, without requiring manual intervention.
49 CFR 192.383 requires EFV installation on service lines up to 2 inches in nominal diameter serving single-family residences, where the service line operates at a pressure sufficient to actuate the valve.