The present invention relates generally to pneumatic or hydraulic actuated relay switching systems and devices and, in a preferred embodiment thereof, more particularly provides a wholly mechanical, fluid pressure actuated sequencing relay device for regulating and controlling the order in which main and wing valve actuators are pressurized and depressurized.
The "Christmas tree" valve configuration in production fluid piping for oil and gas wells is quite common and comprises a regulated main flow supply valve and a diverting pipeline network having paths downstream from the main valve that are opened and closed by secondary valves, known as wing valves.
Some Federal regulations now require a fail-safe valve system at the wellhead in certain oil and gas fields which is operative to assure that if the main valve is opened or closed the wing valves are automatically opened or closed, and vice versa. Therefore, it is advantageous to develop a system to perform a series of operations in a prescribed order so that a fail-safe valve system is utilized and the federal regulations are complied with.
It is well known in the oil and gas recovery and extraction industry that the main valve is to be opened prior to opening the wing valves to initiate production fluid flow. Similarly, when terminating the delivery of the product, it is desirable to close the wing valves first, and then close the main valve, so that the main valve is closed at a "no flow" condition to prolong its operating life.
In the past, the opening and closing sequence of the main and wing valves was effected manually. In recent years, however, the sequential operation of the main and wing valves has been automatically accomplished by a relatively complex system of mechanical sequencing circuits that incorporate a conventional block and bleed relay, a time delay mechanism, and a pilot supply for each valve actuator. It is also well known among those skilled in the art to incorporate time delay circuits between the main valve and wing valves. The circuitry initiates or delays the "open" and "closed" signal to a particular valve so as to promote the proper sequencing.
The major drawback with the conventional systems is an increased propensity for mechanical failure of any one of the numerous components, thereby rendering the entire system inoperable or ineffective.
Therefore, it is desirable to develop a device to sequentially pressurize a first reservoir, before pressurizing a second reservoir, then depressurize the second before depressurizing the first, thereby eliminating the need for the multiplicity of elements in the conventional relay switching system. It is accordingly an object of the present invention to provide such a device for use in a relay switching system.