Gas distribution systems, such as systems used to distribute natural gas, typically transport gas from a producer to a consumer along a series of pipes and through a series of valves. Each gas distribution system may include one or more regulator valves that control the pressure of the gas within the distribution system. Normally, the gas is transmitted at a high pressure through the system. However, the pressure of the gas must be reduced prior to final distribution to the consumers. This pressure reduction is typically accomplished at pressure reducing stations within local networks.
Typically, these pressure reducing stations include one or more pressure regulating valves and some sort of safety device to shut off the flow of gas should the pressure regulating valve fail. Most commonly, slam-shut safety valves are used for this purpose. For example, U.S. Pat. No. 4,134,421, which is hereby incorporated by reference, discloses a slam-shut safety valve that provides overpressure protection in a pipeline. Another example of a slam-shut safety valve is disclosed in U.S. Pat. No. 8,225,812, which also is incorporated by reference herein. The slam-shut safety valve is generally disposed upstream of the pressure regulating valve so that the slam-shut valve may prevent gas from reaching the pressure regulating valve in the event of the pressure regulating valve has failed. The slam-shut safety valve monitors gas pressure downstream of the pressure regulating valve for maximum and minimum pressure tolerances. If the downstream pressure exceeds either the maximum or minimum tolerance, the slam-shut safety valve closes, cutting off the flow of gas to the pressure regulating valve and preventing an uncontrolled leak of gas due to the pressure regulating valve failure.
Known slam-shut safety valves have a valve disc that covers a valve orifice in the vicinity of a valve seat when an overpressure or underpressure condition is sensed. The valve disc is coupled to a reset pin, and the reset pin in turn is attached to an actuator that senses the overpressure or underpressure condition. The reset pin is typically in the open or untripped position, which places the valve disc away from the valve seat in an open position. Should the actuator sense the appropriate trip condition, the actuator releases the reset pin, and the valve disc shifts to the closed position against the valve seat.
In conventional slam-shut devices, the reset pin is exposed to the flow of fluid. Moreover, in certain flow conditions, such as relatively high flow conditions, forces generated by the fluid flow can impact the proper operation of the reset pin, as well as even deform (e.g., bend) the reset pin or otherwise cause alignment problems between the valve disc and the valve seat.