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Broken gas lines can occur during extreme conditions, like earthquakes and floods, or when appliances are improperly moved while being serviced or cleaned. Excess Flow Valves (EFVs) can be installed both at meters and at individual appliances to restrict the flow of gas when an excessive flow (due to a line rupture, or disconnected fitting) is detected.
Excess flow valves have been used for a significant period of time in commercial and industrial applications as a safety and hazard reduction measure. They have come to be used for low-pressure, above-ground applications only since the early 1990's. There are two principal types of these valves.
- Non-Bypass Valves (EFVNB) are designed to trip and close, forming a seal that is essentially gas tight. These valves generally must be reset manually after the leak or rupture has been repaired.
- Bypass Valves (EFVB) allow a small amount of gas to pass through (bypass) after it has tripped, which allows the valve to be automatically reset once the flow has been reduced below the threshold level.
At the present, only bypass valves are used for low pressure applications (after the meter and regulator) within homes. These valves are known as low pressure excess flow valves (EFVs), and close by way of a calibrated float ,spring, or magnet when gas flow that is higher than the rated design is detected. When closed, the bypass valves greatly restrict the flow of gas, allowing only a small quantity of gas to escape. This reduces or eliminates the risk of fire or explosion if properly sized and installed. Since they are bypass valves, they automatically reset after the flow has been reduced below the trip point.
Because excess flow valves rely on gas line pressure variance to sense ruptures, they are sized for each appliance that is serviced by a gas line (or the maximum flow rate of the line) and can be located downstream of the meter or manifold or between the gas service line and the appliance's connection line. These locations are required by building codes to be accessible, so installing EFVs in existing homes should not be a complex undertaking.
Excess flow valves are available for either natural gas or propane gas and can be used with black iron pipe and CSST. Some EFVs are built into the appliance gas connection line. Because gas shut off devices vary depending on the type and magnitude of event that would trigger a valve to close and where and how the valves are installed, only licensed plumbers experienced with gas line sizing should specify and install the devices.
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Excess flow valves can reduce the risk of an explosion due to leaking gas by automatically detecting a line pressure increase caused by a rupture and restricting the flow.
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EFVs are installed in-line with standard gas lines, so installation is very much the same as installing any other gas line fitting. The size and location of the devices is important to proper operation, so plumbers experienced with gas line pressures should perform the work
EFVs vary in size and cost by pipe diameter size and rated flow of appliance. Generally, appliance devices will cost between $65 and $185 each.
Once installed, EFVs do not require energy to operate, and automatically reset after being tripped, so no operating costs apply.
Devices must be tested and approved by a recognized organization such as IAPMO (International Association of Plumbing and Mechanical Officials).
Valves installed in a portion of a piping system operating above 0.5 psi at gauge pressure (psig) shall comply with ASME B 16.33 and those operating below 0.5 psig shall comply with ANSI Z 21.15 or ASME B 16.33.
Not Applicable
Excess flow valves are installed downstream of the gas meter (or propane tank) along the gas line main trunk and/or at each branch to an appliance in a new construction application. Valves can also be retrofitted after the lines have been installed. EFVs are installed in-line with the gas pipe or tubing by the plumbing contractor.
Warranties vary from two years to the lifetime of the appliance being served by the dedicated gas line (an approximate average of 15 years for most appliances).
Gas leakage detection and excess flow valves offer some assurance against the risks associated with gas line rupture. Excess flow valves do not, however, detect or activate in the presence of small leaks. Homeowners that engage service shutoff valves for extended absences from the home and as a precaution when extreme meteorological events have been forecasted would be advised to continue that practice even where EFVs have been installed.
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