Expansible chamber devices – Displacement control of plural cylinders arranged in... – Independent adjustment of opposite stroke limits of single...
Reexamination Certificate
2000-12-14
2002-09-10
Look, Edward K. (Department: 3745)
Expansible chamber devices
Displacement control of plural cylinders arranged in...
Independent adjustment of opposite stroke limits of single...
C251S285000, C092S120000
Reexamination Certificate
active
06446539
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to rotary valve actuators and, more particularly, to apparatus and methods for a dual end stop actuator adjustment.
2. Description of the Background
Actuators, such as a piston activated pneumatic actuators, are well known in the prior art for controlling valves between an open position and a closed position. An exemplary and highly compact configuration for a pneumatic actuator is shown in U.S. Pat. No. 4,354,424, issued Oct.19, 1982, to Sven Nordlund, which is hereby incorporated herein by reference. In that actuator, each actuator piston is provided with a rack having teeth thereon to engage corresponding teeth of an operating element. The rack includes a recess for receiving a first spring that produces a return force on the piston. The recess extends substantially into the rack of the piston. A second shorter spring is provided within a central portion of each actuator piston. Thus, one spring in each piston is offset from the center and is longer than the other spring. The offset, longer spring provides a solution to a basic problem of compact spring return actuators. Prior to this invention, such actuators did not consistently have sufficient spring force to completely close the valve.
Many valves have requirements for drift adjustments that adjust the valve position to an exactly open position and/or an exactly closed position. For these cases, if the valve is not adjusted correctly, the flow path through the valve may not be completely open or accurately closed due to an offset in the valve control element. If the flow path is not accurately controlled, then the system efficiency may be reduced, failures may occur, and maintenance costs may increase. Thus, it is often desirable to have a drift adjustment, or end stop adjustment, for adjusting the valve element for a more precise desired open and closed position. A dual end stop adjustment in the actuator, which is known in the prior art, permits adjustment of the open and closed position for the valve by adjusting the extent of movement of the valve actuator control element. For a rotational valve actuator element, it is known that a dual end stop adjustment has been used to provide two rotational stop positions for the rotational valve element.
The dual end stop adjustment may be used for many thousands of valve openings and valve closings over the lifetime of operation. Prior art end stop adjustments have a tendency change in drift or stop adjustment over time due to many openings and closings to thereby possibly cause deleterious operation of the valve system, significantly increase maintenance costs, and decrease overall system efficiency.
Prior art pneumatic actuators provide that the dual stop adjustment is sealed within the pressure zone of the actuator housing. Thus, the pressurized air, fluid, gas, and the like, used to activate the valve is present at the stop adjustment mechanism. The inventor of the present invention considers this construction to be faulty and may lead to failures and inaccuracies in the stop adjustment. One of the problems is that the pressurized housing is typically limited in size available for actuator mounting so that for a desired piston size, the thickness of the housing is also accordingly limited. The adjustment bolts must therefore extend through the relatively thin wall of the housing so as to be substantially unsupported along their length. Due to this lack of support of the bolts and the relatively thin actuator wall, there is a tendency for bending and warping in prior art actuators either in the bolts or the actuator wall. Thus, the thousands of openings and closings of the valve may well lead to an unstable or effectively non-operational drift adjustment thereby potentially causing valve and/or valve system malfunctions.
The inventor has discovered other problems with existing dual stop adjustments for pneumatic actuators. One such problem concerns end stop bolts for engaging a stop surface wherein the flat head of the end stop bolt is subject to deformation, high spots, and the like which may result in an unstable drift adjustment. Another problem discovered by the inventor relates to the mounting or adapter plate used to secure the actuator to various types of valves which plates thereby adapt the actuator to the particular type of valve. Prior art mounting plates are supported and positioned by bolts that are subject to offsets, bending, and warping which leads to inaccuracies in the dual end stop adjustments as well as the connection to the valve which may require high accuracy to standards, such as for instance, ISO standards. Another discovered problem relates to the machining cost of drilling numerous holes in the mounting plates for support bolts. Depending on the location of the bolts, this can result in additional machining operations so that, according to the inventor, it would be desirable to achieve additional reliability and accuracy with a reduced number of mounting bolt holes. Yet another discovered problem relates to bending and offsets of the rotary drive shaft element due to torque applied to the rotary drive shaft element by the stop adjustment. Yet other discovered problems relate to stress in the mechanical supports for the dual end stop adjustment.
Consequently, there remains a need for a more reliable, consistent, and stable dual end stop adjustment that solves the above-listed unaddressed problems and other problems of prior art pneumatic actuator dual end stop adjustment mechanisms. Those skilled in the art have long sought and will appreciate the present invention which provides solutions to these and other problems.
SUMMARY OF THE INVENTION
The present invention was designed to provide more accurate and reliable operation of a pneumatic actuator to thereby more accurately control valve openings and closings over a lifetime of operation and to avoid deleterious changes that may greatly increase maintenance costs and reduce efficiency of a system of valves.
Therefore, it is an object of the present invention to provide an improved pneumatic actuator.
Another object of the present invention is to provide an improved dual end stop adjustment for a pneumatic actuator.
Yet another object of the present invention is to provide a dual end stop adjustment that does not vary in adjustment even after many, many, thousands of openings and closings of the valve.
These and other objects, features, and advantages of the present invention will become apparent from the drawings, the descriptions given herein, and the appended claims.
Therefore, the present invention may provide for a dual end stop for a pneumatic actuator wherein the pneumatic actuator comprises an actuator housing which has a zone for pressure containment. A rotary drive element is mounted for rotation within the actuator housing. The apparatus comprises elements such as a stop element mounted to the rotary drive element for rotation therewith. The stop element has a first stop surface and a second stop surface. The stop element may preferably be positioned outside of the zone for pressure containment. A first stop member is utilized for engaging the first stop surface. The first stop member, in a preferred embodiment, may be mounted outside of the zone for pressure containment. A second stop member is also utilized for engaging the second stop surface and the second stop member may also preferably be mounted outside of the zone for pressure containment.
In a preferred embodiment, a first bearing is mounted on the rotary drive element on a first side of the stop element. A second bearing is mounted on a second side of the stop member opposite to the first side. In a presently preferred embodiment, the first bearing is mounted in the actuator housing adjacent a stop assembly housing and the second bearing is mounted in the stop assembly housing.
The stop assembly housing may preferably be provided defining an aperture therein. The stop assembly housing may preferably be mounted to the actuator housing
Lazo Thomas E.
Look Edward K.
Nash Kenneth L.
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