Patent Application
20110284791
The present disclosure relates generally to actuators and, more particularly, to a spring seat for use with actuators.
Process control systems typically employ actuators to control or position fluid valves or regulators. Many of these actuators include a return spring, pre-load spring, bias spring, or the like to achieve a desired operational characteristic. For example, some pneumatic actuators used with pressure reducing fluid regulators include a spring that is preloaded via an adjusting screw to set an output pressure of the regulator.
Generally, the springs used in process control actuators are captured between spring seats. In the case of a coil spring, each end of the spring engages a respective spring seat. Spring seats for coil springs typically function to prevent the springs from sliding laterally relative to their longitudinal axes. Further, in some known actuators, one or both of the spring seats capturing a coil spring may be guided seats that tilt relative to a longitudinal axis of the spring to allow the spring seat(s) to remain fully engaged with the end coils on the spring regardless of the orientation and/or deformation (e.g., lateral deflection) of the spring coils.
In one example, a spring seat for use with a pneumatic actuator includes a cylindrically-shaped body. The cylindrically-shaped body includes a shoulder to receive an end of a coil spring; a boss projecting away from the shoulder toward a first surface of the body, wherein the boss is centrally disposed on the body and sized to fit within an inner diameter of the coil spring; and an aperture in a second surface of the body opposite the first surface, wherein the aperture is configured to receive an end of an adjusting screw of the pneumatic actuator such that a wall of the aperture engages the adjusting screw to substantially fix a longitudinal axis of the body relative to a longitudinal axis of the adjusting screw and a longitudinal axis of the spring.
In another example, a spring seat for use with an actuator includes a body having a shoulder to receive an end of an actuator spring; a guide projecting away from the shoulder toward a first surface of the body, wherein the guide is configured to fit within an inner diameter of the coil spring to retain the end coil spring in engagement with the shoulder; and an aperture in a surface of the body opposite the guide, wherein the aperture is configured to receive an end of an adjuster of the pneumatic actuator such the aperture engages the adjuster to substantially reduce tilting of the body and buckling of the spring.
The example spring seat described herein may be used with actuators (e.g., process control actuators) having coil springs for spring return functionality, diaphragm biasing, etc. Known process control actuators typically include an upper and a lower spring seat to capture a coil spring. One of the spring seats (e.g., a lower spring seat) may be fixed to a diaphragm or other operator while the other spring seat (e.g., an upper spring seat) may be coupled to an adjusting device that enables the spring seat to be moved along the longitudinal axis of the spring to adjust a compression height and, thus, load on the spring. During operation, the end of the spring coupled to the spring seat that is fixed to the diaphragm may move with the diaphragm toward and/or away from the spring seat coupled to the adjuster, thereby further compressing the spring or allowing the spring to expand.
In the case where the spring seat coupled to the adjusting device is a guided-type spring seat, this spring seat can tilt relative to the longitudinal axis of the spring. Thus, the longitudinal axis of this spring seat may not be coaxial or even parallel to the longitudinal axis of the spring or the direction of travel of the spring during compression/expansion of the spring. Such tilting of the spring seat can cause the spring to buckle (i.e., the central axis of its coils to curve), which can result in excessive wear or damage to the actuator. For example, in implementations where the coil spring is surrounded by a spring casing, such buckling may cause the spring to contact the inner wall of the casing. Contact between the coil spring and the spring casing inner wall may result in wearing and, thus, thinning of the casing wall, misalignment of other components of the actuator and/or a valve coupled to the actuator, set pressure shift, and/or generally degraded control performance.
In contrast to the above-described known spring seat configurations, the example spring seat configuration described herein fixes the ends of an actuator coil spring such that a longitudinal axis of the example spring seat is held substantially fixed (e.g., parallel or coaxial) relative to a longitudinal axis of the spring casing and the spring. Thus, with the example spring seat described herein, the orientation of the ends of a coil spring may be substantially fixed relative to a longitudinal axis of a spring casing, the direction of travel (e.g., compression/expansion) of the spring, and an adjusting screw or the like. In other words, the example spring seat described herein substantially prevents or reduces tilting of the spring seat relative to the direction of travel of the spring, the adjusting screw, etc. Such a substantial reduction or prevention of tilting of the spring seat substantially prevents or reduces buckling of the coil spring, thereby eliminating the aforementioned problems associated with excessive coil spring buckling.
More specifically, as described in further detail below, the example spring seat described herein provides an aperture that is sized to receive an end of an adjuster such as an adjusting screw. The aperture is sufficiently deep and closely toleranced to substantially prevent tilting movement of the spring seat relative to a longitudinal axis of the adjusting screw. For example, a slight interference fit or minimal clearance may be used between the aperture of the spring seat and the end of the adjuster.
In operation, the actuator rod 116 is operatively coupled to a fluid valve (e.g., a fluid regulator valve) (not shown) and the adjusting screw 124 is turned to set a desired output pressure. During operation, the actuator rod 116 may move upward and downward (in the orientation shown in
The body 200 of the example spring seat 102 also includes an aperture 208 in a surface 210 of the body 200 opposite the surface 206. The aperture 208 is dimensioned to receive an end of the adjusting screw 124 (
Regardless of whether the example adjusting screw 124 or the alternative example adjusting screw 400 is used, the aperture 208 is sized so that movement of the longitudinal axis 214 (
While the example spring seat 102 is described in connection with a pneumatic actuator for use with pressure reducing regulator assemblies, the teachings of the provided example may be more generally applied for use with other types of actuators and/or fluid valves. Also, while the example spring seat 102 is depicted in the orientation of
Additionally, while the example spring seat 102 includes a single aperture that engages an adjusting screw to prevent tilting movement of the spring seat and buckling of the spring, other manners of guiding the movement of a spring seat to prevent tilting of the spring seat could be employed instead of or in addition to the example aperture and adjusting screw configuration. For example, the spring casing may include one or more protrusions extending inwardly to engage respective slots or other features of the spring seat to force the spring seat to move substantially only along the longitudinal axis of the spring casing (i.e., prevent tilting of the spring seat). Alternatively or additionally, the protrusion(s) may be part of the spring seat and the inner wall of the spring casing may include one or more guide channels, rails, etc. to receive or engage the protrusions to guide the movement of the spring seat to be substantially only along the longitudinal axis of the spring casing.
Although certain example apparatus have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all apparatus and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.
