Patent Application
20080197307
The disclosure relates generally to control valves having a valve stem movable for flow rate adjustment and, more particularly, to travel limiters for such valve stems to adjust maximum available flow rate.
Typically, a control valve includes a fluid inlet passage coupled through an orifice to a fluid outlet passage and a closure member disposed in the orifice, which controls the amount of fluid flow therethrough. The closure member may include a valve plug having a surface which engages the orifice forming a valve seat. During operation of a process control system, a process controller may issue a command signal to a control valve to move the valve plug toward or away from engagement with the valve seat to provide a desired fluid flow through the orifice and, therefore, the control valve.
Control valves typically experience variable process conditions during their lifetime. A gas well, for example, may have high pressure when first drilled, but decreasing pressure over time. To maintain constant fluid flow as pressure decreases, the valve must either be disassembled to install a valve seat having a larger flow passage or must be adjusted to allow the valve plug to travel farther from the valve seat to open more port area.
Thus, as a first alternative, to ensure that the valve will achieve the desired flow parameters, separate sets of valve plugs and valve seats may be installed. However, replacement of a valve plug and/or valve seat can necessitate disassembly and reassembly of the valve, which results in additional labor, and additional time the control valve is out of service. Accordingly, it is desirable to be able to achieve a plurality of desired flow parameters by using a single valve plug and a single valve seat.
There are devices which work in conjunction with a valve stem to provide multiple stem travel limits, such as are shown in U.S. Pat. No. 6,905,108. However, the known devices tend to be fairly expensive and difficult to remove and install. This may be due to the tendency to require serrations or threads along the valve stem, as well as along the internal surface of the travel limiting device which engages the valve stem. Also, the devices tend to require removable bolts to fasten pieces together, which may create problems concerning adequate access for manipulation of tools to assemble and disassemble the device, as well as having to deal with multiple loose parts which require care in handling so as not to drop them, while at the same time the difficulty of achieving proper thread alignment when installing bolts, etc.
The more difficult and time consuming manipulation involved with the prior art devices can be particularly challenging when an operator is wearing gloves, such as may be necessary in a cold environment. Given that control valves often are directly mounted on a well head and must cycle, making a change with the prior art devices also tends to require that the system be shut down to avoid the normal movement of the valve stem when the control valve cycles. The time required to remove the prior art devices also is important when an operator needs to completely remove the device, such as to allow the valve to be flushed. Thus, it would be preferable if each maximum flow rate change and flushing operation could be accomplished with less downtime of the control valve, resulting in greater productivity.
In accordance with one example, an apparatus for limiting the travel of a valve stem is provided in a valve having a housing that has a fluid inlet passage and a fluid outlet passage, with an orifice disposed between the fluid inlet passage and the fluid outlet passage. The apparatus further includes a valve plug adapted to move with respect to the orifice to vary the flow of fluid between the fluid inlet passage and the fluid outlet passage, a valve stem connected to the valve plug, with the valve stem having a shoulder disposed along a length of the valve stem that is disposed outside of the housing. The apparatus also includes a valve flow adjustment device having concentric first and second bores having respective different diameters, the valve flow adjustment device being removably connected to the valve stem and engageable with the shoulder, such that the valve flow adjustment device provides two preselected positions that limit the valve stem travel and correspond to two different maximum flow capacities of the valve.
In accordance with another example, a valve flow adjustment device includes a valve stem having a shoulder and a portion of the valve stem extending above the shoulder. The device further includes a removable collar having a passage therethrough formed by concentric first and second bores, the first bore having a first diameter and the second bore having a relatively larger second diameter. The collar also slidably engages the portion of the valve stem extending above the shoulder, and has two preselected positions for engagement with the shoulder with the two preselected positions being adapted to limit movement of the valve stem to two different maximum travel positions.
In yet another example, a valve flow adjustment device includes a valve stem having a shoulder and a portion of the valve stem extending above the shoulder. The device further includes a collar having at least two portions that when joined form a longitudinal passage therethrough having concentric first and second bores, the first bore having a first diameter and the second bore having a relatively larger second diameter, and a radially extending transition wall where the first and second bores meet within the collar. The device also includes a connector adapted to join the at least two collar portions to slidably engage the portion of the valve stem extending above the shoulder.
With the example constructions, a flow adjustment device is provided that limits the travel of a valve stem. The device may include one or more pieces that form a removable, reversible collar around the valve stem. The collar has a passage therethrough having two different bore sizes, with each open to a respective end of the collar. The bores can be formed by having their features cast, molded or machined into the one or more pieces that form the collar. In accordance with the valve flow adjustment device, the flow adjustment device may be assembled to the valve stem to permit two different predetermined stem travel limits.
The valve stem requires a shoulder to engage the removable collar, but no special machining or formation of threads or concentric grooves. Thus, the shoulder may be formed in a variety of ways such as, for example, by a change in valve stem diameter, by a press fit pin at least partially protruding from the valve stem, or by a stop ring inserted in a groove around the valve stem.
Having a shoulder on the valve stem permits the collar to simply be installed in two different end-to-end configurations to vary the valve stem travel between two different predetermined settings. Depending on the orientation of the collar, if the relatively smaller bore is oriented toward the shoulder, it will contact the shoulder and limit the valve stem travel based on the full height of the collar. Alternatively, if the larger bore is oriented toward the shoulder, the shoulder will contact a transition wall formed where the passage changes from the first bore diameter to the second bore diameter, thus limiting the travel by less than the full height of the collar. Thus, the collar may be flipped end-to-end, or inverted, and reinstalled to adjust between the two predetermined valve stem travel limits.
The collar may be held in place via a snap fit, or via other means, such as a spring clip, a latch mechanism, or other fasteners, such as a holding screw or the like. Advantageously, the fastening mechanism(s) may be conveniently made to remain attached to the collar at all times, thereby eliminating the need for loose bolts or screws, and some of the special machining and assembly techniques associated therewith. In turn, the device can be quite small and compact, allowing for shorter, lighter and less expensive valve assemblies having fewer parts. Such devices will require less time to change and, therefore, are more likely to permit rapid changes during normal system operation, between strokes of the valve stem.
Thus, a flow adjustment device is provided that limits the travel of a valve stem. The device provides two different travel limits, which correspond to two different predetermined positions that may be achieved with respect to a maximum valve stem travel and thereby two different maximum flow characteristics for the valve.
The device minimizes the drawbacks of the prior art while permitting a user to quickly change the maximum flow capacity of a valve or to decouple the flow adjustment device entirely via action taken outside of, or external to, the valve housing. Indeed, the operator may be able to make a flow adjustment between strokes of the valve stem, depending on the cycle time. This not only improves productivity by not having to shut down the fluid system, but also reduces operator time and effort, which can have a significant impact financially, as well as to the comfort of an operator working in inclement weather.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and provided for purposes of explanation only, and are not restrictive of the invention, as claimed. Further features and objects of the present invention will become more fully apparent from the following description of the preferred embodiments and from the appended claims.
It should be understood that the drawings are not necessarily to scale.
While other plan and section views are not included, the details such views would show are considered to be adequately shown in the present views or well within the comprehension of those skilled in the art in light of the present disclosure. It also should be understood that the present invention is not limited to the examples illustrated.
Referring now to the drawings,
Passing through the bonnet 14 is a valve stem 40. Valve stem 40 is to be coupled to and driven by the sliding stem actuator at its proximal or upper end 42. The valve stem 40 passes through the bonnet 14 and downward into the valve body 12. In this example, coupled to the lower end 44 of the valve stem 40 is a valve plug 46. The valve plug 46 includes a seating surface on its lower side. It will be appreciated that the valve stem 40 and valve plug 46 may be machined from a single piece, or may be formed in separate pieces for connection by common fastening methods.
The valve body 12 includes an inlet passage 20 and an outlet passage 21. A valve flow path 22 is formed between the inlet passage 20 and the outlet passage 21. Disposed between the inlet passage 20 and outlet passage 21 is an orifice 24. In this example, the orifice 24 receives a removable valve seat 26, although it will be appreciated that a valve seat may be integrally formed in the valve body 12 at the orifice 24. In this example, the valve plug 46 is shaped and sized to permit sealing engagement with the valve seat 26. The valve plug 46 cooperates with the valve seat 26 in the orifice 24 to control the port area through which fluid may flow from the inlet passage 20 to the outlet passage 21. Thus, the flow rate permitted through the control valve assembly 10 is controlled by the position of the valve stem 40 and, therefore, the position of the valve plug 46 relative to the valve seat 26. In
In this example, the diaphragm casing 16 houses a common diaphragm control unit 30 having a diaphragm 32 that responds to control pressures to raise or lower a central mounting hub 34, forming a sliding stem actuator in a manner well known in the art. It will be appreciated that alternative actuator units may be used. Also, the example flow adjustment device would be applicable to many types of valves having a valve stem, whether they are control valves, throttling valves or on/off valves.
By virtue of the vertical movement of the central mounting hub 34 and its coupling to upper end 42 of the valve stem 40, the valve stem 40 and valve plug 46 may move through a range of longitudinal travel in the control valve assembly 10. This range of travel includes, at one extreme, being in a closed position when the valve plug 46 is in sealing engagement with the valve seat 26, and at another extreme, being in a fully open, preselected maximum flow rate position when the valve stem 40 is moved to the full extent of its permitted travel.
In this example, the bonnet 14 has an opening 50 by which an intermediate portion 52 of the valve stem 40 is accessible from outside of the control valve assembly 10. In turn, the exposed intermediate portion 52 of the valve stem 40 has a shoulder 54 formed by an angled transition between a lower larger diameter portion 56 and an upper relatively smaller diameter portion 58. Alternative shoulder formations will be discussed below with respect to examples shown in
The flow adjustment device 60 shown in the example in
In the example shown, each of the collar portions 66 and 68 has an outer wall 70 having a groove or channel 72 formed therein, and has stepped inner walls 74 and 76 formed as semi-circular arcuate reliefs, with a wall 78 at the transition therebetween. The clip 64 is preferably formed of spring metal and in this example has a band shape that is complimentary to the channel 72 of the collar portions 66 and 68. With this example configuration, the collar 62 may be formed by joining collar portions 66 and 68 when the clip 64 is installed in the channel 72 around both portions, as shown in
When the collar portions 66 and 68 are held together to form the collar 62, the semi-circular arcuate inner walls 74 and 76 of each of the collar portions 66 and 68 collectively form a passage 80 through collar 62 having a first bore 74a and a second bore 76a. The inner diameter of first bore 74a is slightly larger than the outer diameter of the smaller diameter portion 58 of the valve stem 40, but is smaller than the outer diameter of the larger diameter portion 56 of the valve stem 40. The inner diameter of the second bore 76a is larger than the lager diameter portion 56 of the valve stem 40.
As can be best seen in
As shown in
In
As with the example shown in
Turning to
A third alternative flow adjustment device 360 is shown in cross-section in
It will be appreciated that this arrangement provides an integral fastener that may be engaged without use of any tools and may be removed by merely prying latch arm 369 to permit the collar 362 to be opened along the fastener side and hinged along the opposite side at integral hinge 363. Thus, the example in
As with the earlier examples shown in
A fourth alternative flow adjustment device 460 is shown in cross-section in
The collar portions 466 and 468 have arcuate inner walls 474 and 476, similar to the examples shown in
A third alternative example of a formation of a shoulder on a valve stem is shown in
Thus, each of the above examples provides a simplified adjustment device that is external to the valve body, yet can create variable effective port sizes by adjusting the fully opened position of a valve plug relative to an orifice, via a valve stem travel limiter. This is a significant improvement over the conventional, more time consuming and, therefore, more expensive practice of having to open the control valve to replace the valve seat or valve plug to change the potential maximum port area, while also providing an improvement over other afore-mentioned more complicated and expensive valve stem and flow adjustment device combinations.
Although certain example devices and articles of manufacture have been described herein, the scope of coverage is not limited thereto. It will be apparent to those skilled in the art that various modifications can be made in the design and construction of such flow adjustment devices and cooperating valve stems without departing from the scope or spirit of the present invention as claimed, and that the claims are not limited to the illustrated examples. Thus, while a flow adjustment device may be provided using any variety of suitable materials of construction, configurations, shapes and sizes for the components and methods of connecting the components, this application covers all devices and articles of manufacture fairly falling within the scope of the appended claims.
