Apparatus and methods to couple actuator stems and rod end bearings

Methods and apparatus to couple actuator stems and rod end bearings are described. An example apparatus includes a bearing having a body and a portion extending from the body in which the portion includes an internally threaded bore. An actuator stem has a first end that includes an internally threaded bore. An externally threaded stud threadably engages the bores of the rod end bearing and the actuator stem to couple the rod end bearing and the actuator stem.

FIELD OF THE DISCLOSURE

This disclosure relates generally to control valves and, more particularly, to apparatus and methods to couple actuator stems and rod end bearings.

BACKGROUND

Automated control valves such as, for example, rotary control valves, are often used in process control plants or systems to control the flow of process fluids. A rotary control valve typically includes an actuator (e.g., a pneumatic actuator, an electric actuator, a hydraulic actuator, etc.) operatively coupled to a shaft extending from a rotary valve via a lever. The lever converts a rectilinear displacement of an actuator stem into a rotational displacement of the valve shaft. Thus, rotation of the lever causes the valve shaft and a flow control member (e.g., a disk, a ball, etc.) coupled to the valve shaft to rotate to increase or restrict the flow of fluid through the valve.

To couple the lever to the actuator stem, a rod end bearing is typically employed. The rod end bearing may include an internally threaded bore (i.e., a female connection) that threadably receives an externally threaded end (i.e., a male connection) of the actuator stem. Alternatively, the rod end bearing may include an externally threaded end that threadably couples to an internally threaded bore of the actuator stem. In either case, the externally threaded portion of the rod end bearing and/or the actuator stem is typically formed by machining bar stock. However, for typical bar stock, the cold-worked, high strength material is concentrated near the outer portion of the bar stock, which is usually machined away during formation of the externally threaded end (e.g., the externally threaded end of the rod end bearing or, alternatively, the externally threaded end of the actuator stem). As a result, the externally threaded end is typically formed from the softer, weaker material near the core of the bar stock.

SUMMARY

In one example, a control valve includes an actuator disposed within a housing having a diaphragm captured between a first actuator casing and a second actuator casing. An actuator stem has a first end and a second end that each include an internally threaded bore, in which the first end of the actuator stem operatively couples to the diaphragm. The control valve further includes a rod end bearing having a bearing retainer and a shaft portion extending from the bearing retainer in which the shaft portion includes an internally threaded bore. An externally threaded stud threadably engages the bore of the shaft portion and the bore of the second end of the actuator stem to couple the rod end bearing and the actuator stem.

In another example, an assembly for use with a control valve includes a bearing having a body and a portion extending from the body, in which the portion includes an internally threaded bore, and an actuator stem having a first end that includes an internally threaded bore. An externally threaded stud threadably engages the bores of the rod end bearing and the actuator stem to couple the rod end bearing and the actuator stem.

In yet another example, a method to couple a rod end bearing and an actuator stem includes obtaining a rod end bearing having a portion with an internally threaded bore and an actuator stem having an internally threaded bore at a first end and coupling the rod end bearing to the actuator stem via an externally threaded stud.

DETAILED DESCRIPTION

In general, the example methods and apparatus described herein provide increased strength to a connection between a rod end bearing and an actuator stem of a control valve. In particular, the example method and apparatus include an externally threaded stud that couples a rod end bearing to an actuator stem. Each of the rod end bearing and the actuator stem includes an end having an internally threaded bore to receive the externally threaded stud.

The example methods and apparatus described herein advantageously replace coupling mechanisms that use an externally threaded rod end bearing end or, alternatively, an externally threaded end of an actuator stem, which, as noted above, are typically formed by machining away the higher strength material concentrated near the outer surface of a bar stock. As a result, the example rod end bearing and actuator stem connection described herein provides greater strength to resist loads (e.g., torsional loads) transmitted to the rod end bearing and actuator stem connection during assembly and/or disassembly of the control valve. For example, the rod end bearing and actuator stem connection described herein substantially reduces twist off or fracture due to inadvertent over torquing or tightening of a fastener when coupling a diaphragm plate to and/or removing a diaphragm plate from the end of the actuator stem opposite the end coupled to the rod end bearing.

FIG. 1is a cross-sectional view of a known rotary control valve assembly100. Referring in detail toFIG. 1, the example rotary control valve assembly100includes an actuator102coupled to a housing104of the rotary control valve100. The actuator102includes a casing106that captures a diaphragm108between an upper casing portion110and a lower casing portion112. The casing portions110and112are coupled together with a plurality of threaded fasteners114spaced along an outer edge of the casing106. The diaphragm108separates the space within the casing106into a control pressure chamber116through which a controlled pressure is supplied via an inlet port118to displace the diaphragm108. A diaphragm plate120couples the diaphragm108to an actuator stem or diaphragm rod122and provides a rigid backing for the diaphragm108. The actuator stem122includes a first end124having an internally threaded bore126that receives a fastener128(e.g., a cap screw) to couple the diaphragm plate120to the actuator stem122.

Springs130,132, and134surround the actuator stem122and are disposed between the diaphragm plate120and respective spring seats136,138, and140formed as shoulders on the lower casing112. Each of the springs130,132, and134provides a biasing force against the diaphragm plate120to return the actuator stem122and any suitable operator (e.g., a flow control member of a rotary valve) coupled to the actuator stem122to a known position in the absence of a control pressure applied to the diaphragm108. The actuator stem122rotatably couples to a lever142via a rod end bearing144.

The rod end bearing144includes a bearing retainer or body146having a shaft or shank148extending therefrom. The retainer body146rotatably couples to the lever142and the shaft148couples to the actuator stem122. At least a portion of the shaft148includes external threads150that threadably couple to an internally threaded bore152at a second end154of the actuator stem122. However, in other examples, the shaft148of the rod end bearing144may include an internally threaded bore that receives an externally threaded portion of the actuator stem122.

As described above, the external threads150of the rod end bearing144are typically formed by machining bar stock with a sufficient diameter to form a connection156between the rod end bearing144and the actuator stem122. However, a typical bar stock provides high strength material concentrated near an outer portion of the bar stock, which is machined away during formation of the external threads150.

During assembly of the control valve100, the rod end bearing144is coupled to the actuator stem122and disposed within the housing104. The springs130,132, and134are then disposed in the actuator casing106to surround the actuator stem122. The diaphragm plate120is then coupled to the actuator stem122via the fastener128. As the fastener128is tightened, the diaphragm plate120compresses the springs130,132, and134, which provides a preload condition.

The torque applied to tighten the fastener128causes the actuator stem122to angularly deflect, thereby transmitting a torsional load to the rod end bearing and actuator stem connection156. However, due to the manner in which machined external threads150are formed, the amount of torque that can be applied to the fastener128to tighten and/or loosen the fastener128is limited. Specifically, if too much torque is applied to the fastener128during assembly due to operator error, the greater torsional load imparted to the connection156may cause twist off or fracture of the smaller diameter, externally threaded end148of the rod end bearing144, thereby causing the connection156to fail. Further, a failure of the rod end bearing and the actuator stem connection156may cause the springs130,132, and134to eject while under compressive load.

Additionally, in some instances during disassembly of the control valve100for maintenance, replacement of components, and/or any other purpose, a greater amount of torque may be required to loosen the fastener128than that was applied to tighten the fastener128. This may result from, for example, corrosion of the valve components (e.g., the fastener128), and/or other factors. As a result, the greater amount of torque required to loosen the fastener128may cause the externally threaded end148to twist off or fracture, thereby causing the connection156to fail. To resist the angular deflection, the actuator stem122may include flats or hex shaped protrusions (not shown) that are engaged using a tool such as, for example, a hex wrench. However, flats are not easily accessible when the actuator stem122is disposed within the housing104. Furthermore, merely increasing the diameter of the actuator stem122and/or the shaft148of the rod end bearing144to machine the external threads150may not be practical because of the space constraints within the actuator casing106and/or increase in manufacturing costs.

Although the control valve100ofFIG. 1Aillustrates a pneumatic actuator102, the example control valve100may use any other type of actuator such as, for example, an electric actuator, a hydraulic actuator, etc.

FIG. 2illustrates an example rod end bearing and actuator stem connection200described herein. In the illustrated example, an actuator stem202includes a first end204having an internally threaded bore206that may be any suitable length (e.g., to prevent the threads from stripping due to tightening). A rod end bearing or spherically shaped bearing208includes a bearing retainer or body210having a shaft or shank212extending therefrom. The shaft212includes an internally threaded bore214that may be any suitable length. An externally threaded stud216threadably engages the bores206and214to couple the actuator stem202and the rod end bearing208. As a result of eliminating the need to machine external threads, the rod end bearing and actuator stem connection200provides greater strength than the rod end bearing and actuator stem connection156described inFIG. 1. Furthermore, the stud216is made of high strength alloy steel and, thus, is substantially stronger than the external threads150of the rod end bearing144ofFIG. 1(or, alternatively, an externally threaded portion of an actuator stem).

Additionally or alternatively, at least a portion of the bore206may include a tapered recess218and at least a portion of the shaft212may include a tapered end or edge220. When coupled together, the tapered edge220engages the tapered recess218to provide a self-locking connection between the actuator stem202and the rod end bearing208. As a result, the rod end bearing and actuator stem connection200further resists the angular deflection of the actuator stem202and the torsional load that may be caused by tightening or loosening a fastener (e.g., the fastener126ofFIG. 1) when assembling and/or disassembling a control valve such as, for example, a control valve300such as that shown and described below in connection withFIG. 3. In the illustrated example, the tapered edge220of the shaft212may be angled substantially similar or complimentary to the angle of the tapered recess218so that the tapered edge220matably engages the tapered recess218of the actuator stem202. However, in other examples, the tapered edge220may have an angle different from that of the tapered recess218.

FIG. 3illustrates an example control valve300implemented with the example rod end bearing208and the actuator stem202ofFIG. 2. The description of those components of the control valve300similar or identical to those described in connection with the control valve100ofFIG. 1is not repeated and the interested reader may refer to the description in connection withFIG. 1for details relating to those components.

Referring toFIG. 3, the rod end bearing208is operatively coupled to the actuator stem202via the externally threaded stud216. The actuator stem202includes a second end302having an internally threaded bore304that receives the fastener128. The fastener128couples the diaphragm plate120and the diaphragm108to the actuator stem202. As the diaphragm plate120is fastened to the actuator stem202, the springs130,132, and134compress and provide a preload condition. Additionally, during assembly of the control valve300, the torque applied to the fastener128to couple the diaphragm plate120to the actuator stem202transmits a torsional load to the actuator stem202, causing the actuator stem202to angularly deflect.

The rod end bearing and actuator stem connection200provides a stronger connection between the rod end bearing208and the actuator stem202to resist the torsional load transmitted by the fastener128during assembly and/or disassembly of the control valve300. Furthermore, the tapered edge220of the shaft212engages the tapered recess218of the actuator stem202to provide a locking condition between rod end bearing208and the actuator stem202, thereby further resisting the torsional load and angular deflection applied to the actuator stem202when turning the fastener128. In this manner, the stronger connection200substantially reduces twist off or fracture of the rod end bearing and actuator stem connection200that may occur as a result of over torquing or tightening due to operator error.

The example rod end bearing208and actuator stem202may be factory installed and/or may be retrofit to existing valves. For example, to retrofit an existing valve such as, for example, the control valve100ofFIG. 1, the rod end bearing144and the actuator stem122are removed and replaced with the example actuator stem202and rod end bearing208. The externally threaded stud216may be obtained or provided to couple the actuator stem202and rod end bearing208. The externally threaded stud216is made of high strength, alloy steel and may be made via machining or any other suitable process(es). The actuator stem202and the rod end bearing208having internally threaded bores206and218, respectively, are obtained or provided via, for example, machining or any other suitable process(es). Additionally or alternatively, the tapered edge220and/or the tapered recess218may be formed via machining and/or any other suitable process(es).

Although certain methods and apparatus have been described herein, the scope of coverage of this patent is not limited thereto. To the contrary, this patent covers all apparatus fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.