Technical Foundation
What Is a Excess Flow Valve?
An excess flow valve (EFV) is a mechanical safety device installed in a gas supply line that automatically restricts or stops flow when it exceeds a preset trip rate — the flow rate expected during a line break or catastrophic leak downstream — while allowing normal appliance demand flow to pass unrestricted. The valve works on a simple differential-pressure principle: a spring-loaded poppet or ball is held open by normal flow and is forced closed once flow (and the associated pressure drop across the valve) exceeds the calibrated trip point.
Trip rate must be selected above the maximum expected normal demand flow of all connected appliances combined, with margin, or the valve will nuisance-trip during normal peak demand (e.g., multiple appliances firing simultaneously) — but trip rate set too high fails to protect against a break downstream of a single smaller appliance line. Many jurisdictions and utilities now require EFVs on new and replaced residential gas service lines as a standard safety measure, following the same principle used for decades on propane tank service lines.
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| Spec | What It Means | Why It Matters |
|---|---|---|
| Pipe Size | 1/2in through 2in nominal | Must match the service line size; EFVs are not universally sized across pipe diameters |
| Trip Flow Rate (SCFH) | Set above maximum combined appliance demand | Set too low causes nuisance tripping during normal peak use; too high fails to protect against smaller downstream breaks |
| Gas Type | Natural gas vs. LP/propane | Valve calibration and materials must suit the specific gas service and its typical operating pressure |
| Installation Point | At the meter, at the appliance riser, at the tank | Determines what section of piping and which appliances the valve protects |
| Reset Method | Automatic reset (bleed-down) vs. manual reset | Determines whether normal service is restored automatically or requires manual intervention after tripping |
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Applications
Where Excess Flow Valves Get Used
Excess flow valves are specified anywhere a gas supply line needs automatic protection against uncontrolled release from a downstream break.
Residential Gas Service Line Protection
EFVs installed at the meter as required by many utilities and codes on new and replaced residential gas services.
Propane Tank Installations
Excess flow valves integrated into propane tank service valves protecting against uncontrolled release from downstream line breaks.
Commercial & Industrial Gas Piping
Excess flow protection on larger-diameter gas supply lines serving multiple pieces of equipment.
Manufactured Home & Mobile Home Gas Service
Excess flow valves protecting gas service lines in installations with higher line-damage risk from ground movement or vehicle impact.
Utility Meter Set Assemblies
EFVs integrated directly into meter set assemblies as standard equipment on new gas utility installations.
Construction Site Temporary Gas Service
Excess flow protection on temporary gas installations during building construction and renovation.
FAQ
Excess Flow Valves Questions, Answered
How does an excess flow valve actually work?
An excess flow valve contains a spring-loaded poppet or ball held open by the pressure differential of normal gas flow. When flow exceeds the valve's calibrated trip rate — as would happen during a downstream line break — the increased pressure differential across the valve overcomes the spring and forces it closed, restricting or stopping flow before it can escape uncontrolled.
How do I choose the right trip flow rate?
Trip rate must be set above the maximum combined demand of all appliances the line serves during normal peak simultaneous use, with reasonable margin — set it too low and the valve nuisance-trips during normal operation; set it too high and it won't reliably protect against a break on a line serving only one smaller appliance.
Are excess flow valves required by code?
Requirements vary by jurisdiction and utility, but many now require EFVs on new and replaced residential gas service lines as a standard safety measure, a practice long standard on propane tank installations. Check local code and utility requirements, since some jurisdictions mandate them broadly while others leave it to the property owner's discretion.
Does an excess flow valve replace the need for a manual shutoff valve?
No — an EFV is an automatic safety device responding to a specific failure condition (excess flow from a major break), not a substitute for a manual shutoff valve used for routine service, maintenance or appliance disconnection. Both serve distinct functions in a complete gas piping system.
What happens after an excess flow valve trips — does it reset automatically?
This depends on the valve design: automatic-reset (bleed-down) valves will reopen once downstream pressure equalizes after the leak is addressed, while manual-reset valves require physical intervention to reopen after tripping. Confirm which type is installed, since assuming automatic reset on a manual-reset valve could leave a system believed to be repaired still without gas flow.
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