Patent Application
20170204987
The present disclosure relates generally to control regulators for fluid process systems and, more particularly, to control regulators including diaphragm assemblies having an integrated pressure relief mechanism.
Process plants, such as refineries, chemical plants or pulp and paper plants, consist of numerous process control loops connected together to produce various products. Each of these process control loops is designed to keep some process variable such as pressure, flow, level, or temperature, within a required operating range to ensure the quality of the end product. Control valves or control regulators within the system manipulate a flowing fluid, such as gas, steam, water, or a chemical compound, to compensate for load disturbances and to maintain regulated process variables as close as possible to a desired control or a set point.
Various control valve configurations may be applicable for certain applications. For example, when a quick-opening valve with a narrow control range is suitable, a rotary control valve, such as a butterfly valve, may be used. Alternatively, when precise control over a large control range is required, a sliding stem control valve may be used. In any configuration, such control valves are generally coupled to a control device such as an actuator, which controls the exact opening amount of the control valve in response to a control signal.
In some systems, especially in pneumatically controlled fluid process systems, the actuator for any given fluid process control device may include a diaphragm actuator. Typical diaphragm actuators comprise a housing containing a spring-biased diaphragm assembly. The diaphragm assembly is operatively coupled via a stem, or other actuator rod, to a valve plug, or other control member, to control the opening amount of the fluid process control device.
Some assemblies include a diaphragm and one or more diaphragm plates. The diaphragm includes a flexible disk-shaped member. The plate or plates are disposed adjacent to the diaphragm and are adapted to be engaged by one or more springs disposed within the housing. Additionally, the plates provide a rigid mechanical connection to the stem. The springs serve to bias the diaphragm assembly into a predetermined position such that the actuator may bias the control device into an open or closed configuration. In some devices, the diaphragm plate includes a dished portion, against which the diaphragm is sealed with a standard worm gear hose-clamp. In other devices, the diaphragm is not fixed to the plate at all. However, the one or more diaphragm plates, as mentioned, are rigidly fixed to the stem of the actuator. Such fixation is generally achieved by threaded attachment. For example, in one form, the stem includes a threaded end portion disposed through a central aperture in the one or more plates. A nut is then threaded onto the threaded end portion of the stem to attach the stem to the plate(s).
When the actuator is exposed to excessive fluid pressure, such as when a supply regulator fails, actuator components are subject to failure, leading to a loss of proper process control and/or to a dangerous situation where high pressure fluid may be sprayed into the environment. To prevent catastrophic failures, some high pressure systems include an external pressure relief valve or a rupture disc to relieve pressure when the pressure exceeds a maximum set point. However, these external pressure relief valves and/or rupture discs add additional costs to the system and are often not used due to the additional costs.
Referring not to
The actuator 10 includes a valve stem 22 connected to a valve plug 24, which slides within the throat 18 of the control regulator 12. During operation, the actuator 12 moves the valve stem 22, and therefore the valve plug 24, relative to a valve seat 19 disposed within the throat 18 of the control regulator 12. A position of the valve plug 24 relative to the valve seat 19 controls a quantity of fluid traveling through the fluid flow-path 20, as may be desired for any given process application.
With reference now to
The housing 26 of the actuator 10 may include an upper housing component 32 and a lower housing component 34. Each housing component 32, 34 may include a plate portion 32a, 34a, a wall 32b, 34b, and a flange 32c, 34c. In one embodiment, the plate portions 32a, 34a may be generally circular. Therefore, the walls 32b, 34b and the flanges 32c, 34c extend circumferentially about the plate portions 32a, 34a. The radial flanges 32c, 34c define a plurality of apertures 36 for receiving fasteners 38 to secure the upper housing component 32 to the lower housing component 34, as illustrated in
The upper housing component 32 may define a fluid port 40 and the lower housing component 34 may define a fluid port 42. The fluid ports 40, 42 are adapted to be coupled to respective fluid supply lines, such as pneumatic supply lines, for varying the pressure within the upper and lower cavities 27a, 27b of the housing 26. Further still, the lower housing component 34 defines an opening 44 for accommodating the stem 22. In other embodiments, one or both of the fluid ports 40, 42 may be removed so that one or both of the upper cavity 27a and the lower cavity 28b may be closed or sealed.
The valve stem 22 operatively couples the diaphragm assembly 28 to the valve plug 24. The valve stem 22 generally includes an elongated rod having a body portion 22a, a threaded end portion 22b, and a shoulder 22c. The body portion 22a includes a diameter that is larger than a diameter of the threaded end portion 22b. The shoulder 22c is disposed between the body portion 22a and the threaded end portion 22b.
The threaded end portion 22b of the valve stem 22 may be coupled to the diaphragm assembly 28 with a nut 48. The nut 48 may be secured to the valve stem 22 with a retaining nut 50. The retaining nut 50 may be threaded onto the threaded end portion 22b of the valve stem 22 and into engagement with the nut 48 to prevent the nut 48 from loosening and backing off of the valve stem 22. The diaphragm assembly 28 may also apply a force to the nut 48, thereby preventing the nut 48 from loosening and backing off of the stem 22.
In the embodiment illustrated in
While the actuator 10 has, thus far, been disclosed as comprising a nut 48 connecting the stem 22 to the diaphragm assembly 28, an alternative embodiment may not require a nut. For example, in one alternative embodiment, the central aperture 71 defined in the upper diaphragm plate 52 may include internal threads. The internal threads of the central aperture 71 may be sized and configured for threaded engagement with the threaded end portion 22b of the stem 22. So configured, the threaded end portion 22b of the valve stem 22 would be disposed in direct threaded engagement with the internal threads of the upper diaphragm plate 52. Tightening the threaded end portion 22b of the valve stem 22 to the upper diaphragm plate 52 would draw the inner radial portions 52b, 54b of the diaphragm plates together, as depicted in
Turning now to
The openings 82, 84 form a locally weakened area on the diaphragm assembly 56. When the openings 82, 84 are aligned with one another, the material of the upper and lower layers 56x, 56z is not supported or reinforced by material in the middle layer 56y. As a result, these areas will fail first (and at a designed pressure limit) when an over pressurization situation occurs. In one embodiment, the locally weakened area will fail at a pressure above normal operating pressure, but below a major component failure pressure. By using the geometry of the openings 82, 84 and the amount of fabric disturbance during an over pressure situation, the system can be designed to fail at a desired pressure. When the locally weakened area fails, the actuator will depressurize, allowing the valve plug to return to its spring fail (or fail safe) position, which can either be opened or closed.
In the embodiment of
In yet other embodiments, for example as illustrated in
In yet other embodiments, for example as illustrated in
While the embodiment of
Any of the embodiments of diaphragm assemblies disclosed herein may be used to advantageously provide an integrated pressure relief mechanism to relieve fluid pressure in an over pressure situation, thus preventing damage to internal components.
Although certain diaphragm assemblies have been described herein in accordance with the teachings of the present disclosure, the scope of coverage of this patent is not limited thereto. On the contrary, while the invention has been shown and described in connection with various preferred embodiments, it is apparent that certain changes and modifications, in addition to those mentioned above, may be made. This patent covers all embodiments of the teachings of the disclosure that fairly fall within the scope of permissible equivalents. Accordingly, it is the intention to protect all variations and modifications that may occur to one of ordinary skill in the art.
