|B. P. (Bob) Urbanowicz|
B. P. (Bob) Urbanowicz is the president of Samson Controls, Inc., USA. Since joining Samson Controls in Canada in 1985, he has held various positions, including President of Samson in Canada. He earned his master’s degree in Mechanical Engineering from the Gdansk University of Technology in Poland. Samson Controls, Inc. is a subsidiary of Samson AG of Frankfurt, Germany. Samson has been manufacturing control valves, actuators and instrumentation since 1907. Mr. Urbanowicz can be reached at email@example.com.
Q: How has valve actuation and control technology evolved over the past 10-20 years? How is the valve actuation technology of today better than previous generations of valve actuation technology?
A: The fundamentals of control valve and actuator technology have developed in an evolutionary way during the last 20 years. New design ideas, improved production methods, new materials and extensive use of computer systems have led to significant improvements. Present-day valves are more compact, have higher shutoff capability, and more advanced sealing technology, especially with the bellows design. Their resistance to erosion and corrosion has also improved, and the anti-cavitation and noise-reducing trims are more advanced. As a result, modern valves are more reliable, have longer service life, and provide for lower cost-of-ownership than the valves of the previous generations.
|Current-generation valve positioners are capable of pinpointing valve faults as well as emerging conditions and communicate these findings over HART, Profibus or FOUNDATION fieldbus to the process control system.|
The introduction of digital technology revolutionized the development of valve positioners. HART, Foundation Fieldbus and Profibus have enabled the market to expand the scope of functions in these instruments and their integration into modern plant asset management systems. The recent developments in wireless technology have opened new possibilities for valve users as well.
Q: How do manual, electric, pneumatic, and hydraulic valve actuation methods differ? In what sort of application environments is each actuation method typically a good fit?
A: Let’s start with the most often used actuators – the pneumatics. The automated and control valves in process plants are usually operated by pneumatic actuators. They are, by far, the most commonly used actuators due to their being light weight and rugged. Their low cost and high reliability make them very popular. Pneumatic actuators are commonly used in a potentially explosive atmosphere. The failsafe action of single-acting actuators is system-inherent.
Manual shutoff valves are used to isolate or bypass control valves. They are only occasionally operated and used for on/off applications, when the response time is not critical.
Electric actuators are mainly used in applications where compressed air is not available; for example, in small systems for building automation, or in some areas of power plants. However, the implementation of failsafe action (fail open or fail close) upon power supply failure or emergency shutdown in large electric actuators requires a technically complex construction.
Hydraulic actuators are used in applications where the required force and/or stroke cannot be accommodated by pneumatic or electric actuators.
Q: What is the difference between a rotary valve actuator and a linear valve actuator? What are some common applications/examples of each actuation method?
A: Linear actuators are used to actuate linear valves such as globe, three-way (diverting or mixing) and angle valves. Pneumatic linear actuators have the simplest construction and provide very precise control of flow.
Rotary actuators, with shafts performing up to 90-degree rotary motion, are mounted on rotary valves such as ball, butterfly, rotary plug and segmented ball valves. These actuators are derived from linear actuators, and use a gearbox or lever system to convert the linear into a rotary motion. The actuator construction, where compressed air acts on a rotary vane instead of a piston, has not established itself on the market.
In contrast to the pneumatic version of rotary actuators, the rotary motion of electric actuators is inherent. A complex linear unit is needed to transform the rotary motion into a linear stroke. It would be beyond the scope of this interview to go into details of the individual construction of these actuators.
Q: What role do valve positioners play in valve actuation and control applications?
A: We very often describe the positioner as the brain and heart of the control valve, because its functions and capabilities are so comparable. Analog positioners are used to precisely convert the input signal from a controller or control system and control the valve position correspondingly, despite various actuator bench ranges and disturbance variables, such as varying supply air, dynamic forces affecting the valve plug, and valve stem friction. In addition, positioners are responsible for adapting the inherent characteristic of butterfly and ball valves to the required characteristic form.
At the present time, digital positioners are expected to perform additional tasks, such as automatic startup and self-diagnostics, as well as many asset management functions, which enable predictive, status-oriented maintenance of control valves.
Q: What are the key specifications users must evaluate when considering valve actuation?
A: Generally, the user decides whether manual, pneumatic, electric or hydraulic actuation is to be used to operate the actuator. Manual actuators can only be used for on/off purposes where the response time is not critical and the valve is accessible. For all other applications, it is important to decide which auxiliary power is available. The valve supplier then chooses the actuator to match the valve and operating conditions such as shutoff pressure, differential pressure, flowrate, leakage class and closing time at minimum, normal and maximum load.
Q: What are some of the common pitfalls end-users need to be aware of when specifying valve actuation and control technology for a given application?
A: As already mentioned, the valve suppliers specify the actuator. They calculate the necessary nominal forces over the entire travel range or angle of rotation, and also take into account the actuator stiffness, for example, to operate the valve in the flow-to-close direction. For processes that require fast responses, the valve supplier specifies the tube size connecting the positioner with the actuator and, if necessary, installs a booster to increase the air capacity of the positioner.
For the control valve technology, flashing and cavitation are two troublesome conditions that can quickly destroy the valve. Depending on the cavitation level, several methods can be employed to reduce or eliminate its effects. Flashing can be prevented by adjusting the process conditions. Special materials can also be used to prolong the life of a flashing or cavitating valve.
Q: What are some key steps end-users can take to ensure they are employing the appropriate valve actuation solution for a given application?
A: For end-users, the question focuses on which type of actuator (pneumatic, electric or hydraulic) works most cost-efficiently and reliably for the given process. After carefully weighing all the pros and cons, end-users will surely reach the conclusion that pneumatic actuators are the best solution in large processing plants, in which a compressed-air supply network already exists for other tasks. These actuators are compact, exceptionally rugged, reliable, require little maintenance and are excellent value for the money. They can be used in hazardous areas without any complications and have an inherent failsafe action.
In places where a compressed-air supply network does not exist and just a few control valves are to be actuated, the electric actuator is probably the most cost-effective solution.
The scope of use for hydraulic actuators is relatively small. They find use in applications where extremely high positioning forces and long, fast stroking are required.
Q: How do you envision valve actuation and control technology evolving of the next 10-20 years? How will the valve actuation and control technology of tomorrow be better than the valve actuation and control technology of today?
A: The fundamentals of the control valve and actuator technology will not see dramatic changes; they will continue to develop in an evolutionary way, fine-tuning the areas of design, production and application of new materials.
Major innovations are to be anticipated in the field of valve positioners. More powerful sensors will be used in combination with positioners to precisely detect the valve faults and failures that, up to now, can only be identified indirectly.
There are two other areas where future development will have major impacts on control technology – wireless communication and Safety Instrumented Systems (SIS). More and more systems that are being built take advantage of wireless technology. Also, SIS is quickly gaining in importance with end-users. These new areas are developing very rapidly.
The valve actuation and control technology of tomorrow will be safer and more economically viable.