Pacific Seismic (PSP) valves are earthquake-sensitive gas shut-off valves. They are intended to close in the event of an earthquake to prevent gas flow into a structure where earthquake damage may have occurred. The valve reduces the potential for fire or explosion due to the release of natural gas into a  structure where there are gaslines, gas fixtures, or gas appliances.

PSP valves do not use any source of internal or external electrical power. They are designed to remain closed until manually reset. The valves are intended to be mounted in the gasline up-stream or down-stream of the gasline pressure regulator and gas meter outside the structure. These valves do not replace the manual up-stream shut-off valves provided in the gas service line.

A PSP valve consists of a swing-check valve arrangement with an acceleration-sensitive trig-gering mechanism. The trip mechanism consists of a steel ball resting on a tapered cup-shaped support. The horizontal motion of an earthquake causes the ball to move from the center of the support. This allows the ball's mass to act upon the movable pipe of the trip mechanism, activating the valve and initiating closure. Springs assist the valve-flapper to close and gas pressure assists in holding the valve disc in the closed position. The trip mechanism is factory set and sealed. A sight glass is provided so that the Open or Closed indicator can be seen and the trip mechanism status of the valve can be easily determined.