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As one would expect there has been a significant increase in the sales growth and usage of automated valves...
By Gary S. Hobson
Featured in the March, 1998, Vol. IV, No.3 Issue of Flow Control
As one would expect there has been a significant increase in the sales growth and usage of automated valves over the last ten years. The Valve Manufacturers Association of America (VMA) numbers indicate a 49% increase in 1996 over 1987. The VMA numbers also indicate that automated valves comprise approximately 30% of all domestic industrial valves shipped in 1996. The growth of automated valves should continue as technology advances the capability of plants and end users to integrate all valving into their systems and processes leading to greater efficiencies and competitive advantages.
Automated valves are valves mated with an actuator to automatically stroke gate, globe, ball, plug, butterfly and other types of design. Specific valves are used for certain applications based either on tradition or often on subjective requirements from the user's personal experience. As discussed in previous articles in this magazine, actuator types are specified based on criteria such as type of valve used, tradition, subjective input, motive force available, and site location. Today's market offers an enormous variety of designs in both valves and actuators. In addition there are large numbers of accessory items to complement the automated package, including position indicating limit switches, positioners for throttling control, solenoid pilot valves, manual overides, local/remote push-button stations and tie-ins to distributed control systems. Many of these control accessories are available in various analog as well as digital signals.
Quarter-turn valves, such as ball, plug, and butterfly tend to be more easily automated. The same quarter-turn resilient seat and seal designs which deliver tighter shut-off and stem sealing in many services also requires less torque output from an actuator. Movement is a rotary 90 degrees or 180 degrees which is simple to automate. Low torque is encountered due to position seating into resilient seat materials. This in contrast to other types of valves which drive a wedge or other sealing device into a mating surface using multiple turns of the stem or a linear jamming effect on the stem/plug to get a tight shut-off. Actuators for quarter-turn valves are more compact, energy efficient, and inexpensive.
Problems Associated with Conventional Actuator Mounting
Current designs for quarter-turn valves incorporate a surface or pad for mounting holes to bolt to actuator brackets. Conventional mounting practice is to install a bracket and adapter between the mounting pad and the mounting surface of the actuator. The adapter or coupling is aligned with the valve stem and the drive sleeve or output stem of the actuator. The bracket is then bolted to the valve and bolted to the actuator. The size of the bracket is dependent upon whether the valve is coupled to an actuator with a male output or a female drive sleeve in the actuator. It is also relative to where the mounting holes on the valve are located; directly beneath and surrounding the valve stem or off to the side cast into the body of the valve. Sometimes mounting pads are integral to the top of the flange connections of the valve. All of which affects size and weight of the bracket. The length and size of the coupling/adapter is subject to the same parameters. Generally, all the concern and attention is focused on the valve and actuator. Little consideration is given to the method of mounting the valve and actuator together. But, in fact, the bracket and adapter can often be the source of failure for valve/actuator packages. If the bracket is warped, however slightly, or the bolt drillings are off, side-loading of the stem can occur. If the coupling is too long and bracket bolts are drawn down tightly the coupling can jam the stem of the valve into the plug, ball, or bearing surface of the valve resulting in higher torque than the actuator can provide.
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