An excess flow valve is an automatic safety valve on the underground gas service line between the street main and your meter. If that line is broken or cut, the valve closes and restricts the flow of gas. It won't stop a leak inside your house or at an appliance, and some gas can still escape after it closes.
What does an excess flow valve do?
It limits how much gas can pour out of a broken service line. Southwest Gas's Arizona brochure says an EFV "automatically closes and restricts the flow of natural gas if an underground pipe is broken, completely cut, or torn apart," and that "Such damage usually results from some type of excavation or digging." It adds that an EFV "may also restrict the flow if the gas meter is damaged," such as from a vehicle hitting it.
The payoff is fewer fires and explosions after a line strike. In the utility's words, "Because an EFV restricts the flow of gas, it reduces the potential for explosions, fires, and personal injury."
Think of it like a circuit breaker for the service line. Normal use doesn't trip it. A sudden flood of gas through a break does.
### Is an excess flow valve the same as my gas shutoff?
No. The EFV works on its own, out of reach on the utility's buried pipe, while the shutoff valves are manual valves you or the utility can turn.
| Device | Where it is | What closes it |
|---|---|---|
| Excess flow valve | Buried on the service line, near the main | Closes by itself when a broken line lets gas rush out |
| Meter shutoff valve | On the pipe rising to the meter | You or Southwest Gas, with a wrench |
| Appliance shutoff valve | On the gas line next to each appliance | You, by hand |
| Seismic shutoff valve (optional) | Customer side, installed by a contractor | Closes by itself in a strong earthquake |
The EFV is the only one you can't reach. Under 49 CFR 192.381, an operator must locate it "as near as practical to the fitting connecting the service line to its source of gas supply." That gas supply is the main, which Southwest Gas's brochure places in or near the street, alley or easement. For the valve you can operate, see how to turn off the gas to your house.
What won't an excess flow valve protect against?
Most of the leaks a homeowner is likely to run into. Southwest Gas lists them plainly: installing an EFV "won't protect against customer appliance malfunction, customer houseline gas leaks, small punctures in the underground pipe, or gas meter leaks." It "may not protect against damage to pipelines from earthquakes or flooding."
Two points follow from that:
- It only guards the utility's pipe. The valve sits on the service line upstream of the meter. A leak at your water heater, a loose dryer connector, or a corroded buried line running from the meter to the house is past the valve. It won't notice.
- It doesn't make a broken line safe. The same brochure warns that an EFV "doesn't shut off the flow of gas completely. Some leakage may still occur and result in a hazardous condition."
So a gas smell always gets the same response, EFV or not. Leave the area without touching switches, then call 911 and Southwest Gas at 877-860-6020 from a safe place. Our page on what to do when the house smells like gas walks through it.
### What if someone hits a gas line while digging?
Treat it as a leak whether or not the line has an EFV, because the valve limits the flow but doesn't stop it. Move people away, keep sparks out of the area, and call 911 and Southwest Gas from a safe distance. The bigger lesson is where the gap sits. Southwest Gas warns that "customer buried piping can't be located by calling 811." The yard line from your meter to the house, a pool heater or a grill isn't marked by 811, and it isn't covered by the EFV either. Southwest Gas says a licensed, qualified plumber or contractor can help you find that customer buried piping, and to "Hand dig when excavating near any buried gas piping."
Does my house have one?
Maybe, depending on when the service line went in. Southwest Gas says it "has installed EFVs on most new or replaced service pipelines installed after June 2008." For lines to single-family homes installed or replaced after April 14, 2017, 49 CFR 192.383 requires one "before the line is activated," with a few exceptions, such as a line that doesn't run at 10 psig or more all year.
You can't see it from the yard, so ask. Southwest Gas's brochure says to call 877-860-6020 to find out if you have one, and its safety page also lists its Energy Specialists at 800-654-2765 for EFV questions.
Can I get one added to an older gas line?
Yes, in most cases. Federal rules give existing customers a right to ask. Under 49 CFR 192.383, a customer whose service line doesn't exceed 1,000 SCFH, and doesn't fall under one of the listed exceptions, "may request an EFV to be installed," and the operator "must install the EFV at a mutually agreeable date." Southwest Gas's Arizona tariff goes further than the federal floor, letting customers request one when the load doesn't exceed 5,500 SCFH.
Here's what to expect:
- You pay for a retrofit. The tariff says the utility will tell you "any costs associated with the installation that shall be paid by the Customer." Southwest Gas's brochure says customers who choose an EFV "will be responsible for installation costs," which vary with site conditions. Ask the utility for its current figure.
- The utility does the work. The brochure says only Southwest Gas or its approved contractors may install one, so this isn't a job for your plumber.
- It's a dig job. The brochure says installation "involves construction work and excavation of the service pipeline," gas service may be interrupted, and paving or concrete repair can come later.
- Some lines don't qualify. A line that doesn't run at 10 psig or more year round, a system with contaminants that could foul the valve, or a service too large for an available EFV can be turned down.
New and replaced lines are different. On those, the tariff says the utility pays the EFV costs, with narrow exceptions such as a relocation done only for the customer's convenience. If you're getting gas service to a house for the first time, the valve comes with the new line.
### Should you tell Southwest Gas before adding appliances?
Yes, tell the utility before you add a big gas appliance. The tariff requires applicants to give Southwest Gas "information concerning the gas usage and demand requirements" so the valve is built so that "suitable gas capacity is available." The same tariff makes it "the customer's responsibility to notify the Utility of changes in their load requirements." Before adding a tankless water heater or a gas line for a pool heater, have your plumber check the house pipe and give Southwest Gas a call about the meter side.
What should you take away?
An EFV is good protection against one specific accident: a service line torn open by digging. It does nothing for leaks inside your house or on your side of the meter. Keep calling 811 before you dig. The brochure says to call "at least two working days before starting a project" and to use hand tools within 24 inches of marked gas lines. Also keep up with regular checks of your gas lines, because the pipe past the meter is yours.
HQ Plumbing & Air handles gas leak detection and repair on the customer side of the meter, with 24/7 emergency service across the Phoenix area.