Gas shut-off valves for seismic areas

comments (1) September 1st, 2010 in Blogs

Justin Fink, Senior Editor

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The Northridge Valve has only one moving internal part. A stainless steel ball rests on a pedestal inside the valve when it is in the ON position allowing gas to flow freely. If theres a seismic disturbance of 5.2 or greater on the Richter scale, the stainless steel ball falls from the pedestal and plugs the gas outlet. The gas can only be turned back ON by manually resetting the valve (the faceplate has a magnet concealed behind it that lifts the stainless steel ball back onto the pedestal when it is slowly rotated one full turn counterclockwise) so theres no waiting for the gas company.

The Twingate Valve relies on a pair of Teflon coated brass gates that resemble plumb bobs. Each valve has two chambers; each chamber houses a brass gate mounted on a stainless steel pin. These pins are offset ninety degrees so that at least one gate will always be in position to react by rocking off its pin into its seated position. Closure of only one gate is necessary to stop the flow of gas, and the valves can be reset by pulling up on the reset sphere.

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When the ground and the house shake, so do the pipes within. So it's no surprise that the most common cause of earthquake related fires is gas leaks. All it takes is a ruptured pipe and a spark for ignition.

If you live anywhere in the UBC's "Extreme" (red) or "High" (orange) risk zones - shown in the map above- and have natural gas appliances, you are at risk.

Many houses in the affected portions of the country are required by building code to have an automatic gas shutoff valve. Installed as an in-line component on the house side of the meter, these valves are anchored to the structure of the building (or to the ground, in some cases) and, when disturbed by an earthquake of a predetermined magnitude, close off to stop incoming gas.

THE BAD NEWS: These valves are only being enforced in new construction and major renovations, so many existing houses are unprotected.

THE GOOD NEWS: These valves aren't that expensive (usually around $100-$150), and are relatively simple to install.

A more extensive list of devices approved by the State of California,

Code Check Building for California
by Douglas Hansen, Redwood Kardon, Paddy Morrissey An illustrated guide to the newly adopted 2008 California building code $18.95 more info...

posted in: Blogs, safety, plumbing

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Comments (1)

InspectorDude writes: A couple of corrections, if I may. These seismic gas shut-off valves have to be installed at the point-of-sale in most real estate transactions in the Los Angeles area. The minimum cost (including installation) is $400.00 and must be inspected by the city.
Posted: 12:21 pm on September 6th

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