Earthquake Gas Shut Off Valve: How Seismic Valves Work

What does an earthquake gas shut off valve actually do?

It closes the gas, and that is the whole job. A weight sits balanced inside the valve body, and when the ground moves hard enough that weight falls off its seat and drops a plate across the gas path. No wiring, no battery, no signal from anyone. The Department of Energy's Building America guide puts the trigger at shaking equivalent to roughly a magnitude 5.4 and notes the device stops flow at the first sign of earth movement, whether or not a pipe broke (Building America Solution Center).

What it will not do is find a leak. It assumes a big enough quake broke something and cuts supply before a damaged line can feed a fire. That assumption is the feature and also the cost, because it will shut your gas off on days when nothing is wrong.

Seismic valve or excess flow valve, what is the difference?

The two get sold in the same conversation and they are not the same device.

• A seismic valve reacts to motion. It lives on your house line past the meter, above ground, and it trips on shaking.
• An excess flow valve reacts to volume. It sits underground on the utility service line between the gas main and your meter, and it closes when gas suddenly starts moving much faster than normal, which is what a backhoe through a service line looks like.

So an excess flow valve does nothing in a quake unless the buried pipe is actually severed, and even when it trips it is not a hard stop. SoCalGas makes the point plainly: the valve restricts the gas rather than ending it, and some leakage can still occur (SoCalGas on earthquake and excess flow valves). Only the seismic one is yours to buy.

Where does the valve go, and who is allowed to install it?

On your side of the meter, on the house line, usually outside on the riser between the meter and the wall. It never goes on utility hardware, and one found bolted to utility equipment gets removed. PG&E does not install these, though it will shut the gas off for the work and turn it back on afterward.

Two requirements are not negotiable in California. The valve has to be a model certified by the Division of the State Architect, which certifies against ANSI/ASCE/SEI 25-16, the standard for earthquake actuated automatic gas shutoff devices. And a licensed plumbing contractor has to set it per the manufacturer's instructions. State law defines customer-owned piping as everything downstream of the utility point of delivery, including downstream of the meter and service tee (California Health and Safety Code 19201).

Some cities and counties also require these devices on new construction, significant alterations, and additions, so ask your building department before you buy anything. We pull the permit, and the line gets pressure tested with that test witnessed at inspection, same as any gas work we run under CSLB #1036920. Our gas line repair page covers the rest.

Will an earthquake gas shut off valve lower your insurance?

By itself, probably not, and the sales pitch tends to blur this. The California Earthquake Authority's Hazard Reduction Discount goes up to 25 percent, and it applies to one to four unit wood framed houses built before 1980 on a raised or other non-slab foundation. What earns it is bracing the cripple walls, anchoring the house to its foundation, and a properly secured water heater (CEA premium discounts). A gas valve is not on that list. Water heater straps are already required on every existing residential tank in the state, and we cover that in the rental turnover checklist.

Ask your own carrier before you spend money expecting a credit. A homeowners policy and an earthquake policy are separate products with separate rules.

What is a nuisance trip, and how do you reset the valve?

A nuisance trip is the valve closing when nothing broke. A loaded truck going by, a ladder leaned against the riser, or a small quake far too weak to hurt anything. Installers hang a stabilizing bracket on the piping near the valve for exactly this reason, to keep a bump from dropping it. You will know it happened because every gas appliance quits at the same moment: no hot water, no furnace, no burners, and the indicator on the valve reads shut.

Resetting is mechanical, usually a small tool turning a reset stem, and the manufacturer's instructions are the ones that matter. The part people underestimate is what comes after. Every pilot in the house went out when the gas stopped, so the appliances need checking and relighting before anyone walks away. Utilities recommend a qualified professional handle the reset along with a safety check, and SoCalGas charges a fee for resets caused by something other than an earthquake, which tells you how often these get tripped by accident.

If the valve tripped in a real quake, do not reset it and start lighting pilots. Have the piping checked first. And if you smell gas, get out and call PG&E from outside. What the utility fixes and what we fix is laid out in our gas leak guide.

Is one worth installing on a North Bay house?

USGS puts the chance of a magnitude 6.7 or larger earthquake in the San Francisco Bay area at 72 percent over the next 30 years (USGS earthquake probability). The Rodgers Creek fault runs straight through Santa Rosa, so nobody in Sonoma County is far from it.

The case is strongest where nobody can get the gas off fast: older homes with long runs of steel house line, a buried feed out to a detached garage, rentals where the tenant has never seen the meter, and anyone who does not keep a wrench at the meter. It is weakest if you heat with gas and the valve sits somewhere it will trip on passing trucks, because every trip means a cold house until someone resets it.

Either way, learn where your manual shutoffs are. The gas cock at the meter takes a quarter turn with a wrench, and the water side is worth the same ten minutes: our guide on shutting off the water main walks through where to look. If you want a seismic valve priced, or you have one that tripped and you are not sure the line is sound, call (707) 308-5599. We answer 7 days a week and the quote costs nothing.