1. Field of the Disclosure
The disclosure generally relates to slam-shut safety devices for gas distribution systems, and specifically relates to fail safe retaining plug assemblies for slam-shut type safety valves.
2. Related Technology
Gas distribution systems, in particular natural gas distribution systems, 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. patent application Ser. No. 12/105,351, which is hereby 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 a pressure regulating valve failure. 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 retaining plug attached to a reset pin. A safety disk is attached to the retaining plug. The safety disk covers a valve orifice in the vicinity of a valve seat when an overpressure or underpressure condition is sensed. The reset pin is attached to an actuator that senses the overpressure or underpressure condition and the reset pin, and thus the safety disk, is spring loaded to an open position.
The safety disk is typically retained on the retaining plug with an e-ring or other similar locking connection. The retaining plug is likewise attached to the reset pin with an e-ring or other locking connection. The e-ring or other locking connection must be removable for valve maintenance or repair so that individual components may be repaired or replaced as needed. However, these removable locking connections, and e-rings in particular, are susceptible to failure when exposed to the fluid pressure moving through the control valve. If the e-ring or other locking connection fails, the safety disk and/or the retaining plug may become disengaged from the reset pin, causing a failure of the slam-shut safety valve. It is essential that the slam-shut safety device remain operational because the slam-shut safety device is attached to the control valve to prevent fluid flow through the control valve in the event of control valve failure.