Fluid control devices include various categories of equipment including control valves and regulators. Such control devices are adapted to be coupled within a fluid process control system such as chemical treatment systems, natural gas delivery systems, etc., for controlling the flow of a fluid therethrough. Each control device defines a fluid flow-path and includes a control member for adjusting a dimension of the flow-path. For example, FIG. 1 depicts a known regulator assembly 10 including a valve body 12 and an actuator 14. The valve body 12 defines a flow-path 16 and includes a throat 18. In FIG. 1, the regulator assembly 10 is configured in a flow-up configuration. The actuator 14 includes an upper actuator casing 20, a lower actuator casing 22, a diaphragm subassembly 30 including a diaphragm 32, and a control member 24.
The control member 24 is disposed within the upper and lower actuator casings 20, 22 and is adapted for bi-directional displacement in response to changes in pressure across the diaphragm subassembly 30. So configured, the control member 24 controls the flow of fluid through the throat 18. Additionally, as is depicted, the regulator assembly 10 includes a seat ring 26 disposed in the throat 18 of the valve body 12. When the outlet pressure of the valve body 12 is high, a sealing surface 28 of the control member 24 may sealingly engage the seat ring 26 and close the throat 18. Similarly, absent any pressure in the actuator 14 or upon the failure of the diaphragm 32, a coil spring 34 disposed within an annular cavity portion 36 of the upper actuator casing 20 biases the control member 24 into the closed position. Such a regulator is commonly known as a “fail close” regulator.
“Fail close” regulators are configured such that upon the occurrence of a leak in the system, which removes pressure from the actuator 14, or a failure of the diaphragm 32 such as a tear, the control member 24 automatically closes the flow of fluid through the regulator 10. Under such a circumstance, fluid delivery to the desired end-location ceases until the regulator is repaired.
To avoid the necessity of terminating fluid delivery under failure conditions, some fluid process or delivery systems incorporate a “fail open” regulator. “Fail open” regulators operate similar to “fail closed” regulators; however, upon failure of the diaphragm, a spring biases the control member open, rather than closed. Thus, even when the diaphragm or other control component fails, fluid continues to flow through the regulator uninterrupted and uncontrolled. Such configurations therefore often include a monitor regulator, which controls the fluid flow when the “fail open” regulator fails.
Conventional regulators are generally configured as either “fail open” or “fail close.” To reconfigure a “fail open” regulator to operate as a “fail close” regulator, or vice versa, the control assembly and the regulator casing often must be reconfigured or replaced with a different control assembly and regulator casing. Such reconfiguration and/or replacement of the regulator casing can be costly and time-consuming.