Earthquake Valve

An earthquake valve or seismic valve is an automatic way to shut off the low pressure regulated gas supply to a structure during a major earthquake and/or if a pipe is broken. These are applicable both to utility supplied natural gas and to gaseous liquified petroleum gas (LPG). These small devices are installed on the property gas meter (usually between the utility company's metered installation and the structure piping) and are designed to instantly stop the natural gas supply in order to protect the structure if a gas leak or line break occurs during an earthquake.

Fires or explosions due to gas line breaks can be more damaging than the actual earthquake itself.

The utility companies recommend you shut off your gas immediately after an earthquake if you smell gas. If you are at work or away when an earthquake hits, then you may not be able to get home in time. An earthquake valve will take care of this instantly for you.

These devices should be installed by licensed contractors and it can cost anywhere from $300 to $500/per meter for installation which should include parts and labor.

Types of valve
Two types of valve are commonly employed, one is sensitive to motion and the other to excessive gas flow. The most secure installations would use one of each type connected in series.

Motion sensing caged ball
A metal ball is retained away from an orifice by sitting upon a ring. Any shaking of the mechanism will cause the ball to roll of its ledge and fall down to block the orifice. it is reset using either an external magnetic device or an internal lift mechanism. If too sensitive it may be triggered by passing vehicles on a rough road. In the case of a severe seismic event, the gas piping should be completely inspected for breaks before resetting. Since all pilot lights will go out, some appliances must be properly restarted once the device is reset.

Excessive flow sensor
A valve is closed when the flow exceeds a certain limit appropriate to the application. This will only operate when a pipe is broken, and so may not operate if a small (yet potentially dangerous) leak is present. If activated, any faults in the piping must be first repaired.

References and illustration

 * Website of a commercial provider and installer