Process control is a lot like baking, says Jerry Butz, Director of Engineering and Technical Support here at Automation Service.
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Baking requires specific quantities of ingredients and a steady supply of heat. To keep the oven at the desired temperature, your oven thermostat takes measurements and sends the data to a controller, which then turns the heating element on or off as required.
Recipes in the process industry specify variables like the level in a tank and the flow rate in a piping system. To keep those variables steady, a sensor takes measurements and sends the data to a controller, which then throttles a control valve as required.
As you can see from these examples, control systems work in three basic phases:
a variable (temperature, pressure, flow, etc.)
that measurement to the desired level (i.e., the setpoint)
the system (e.g., open or close a valve) whenever there&#;s a discrepancy between the measured value and the setpoint
Read more about how controllers work here: Proportional Only vs Proportional + Reset Control
To achieve precise control, the speed and accuracy of all of these stages are important. Here, we&#;ll dig into how you can boost the speed and accuracy of the last phase &#; opening or closing a control valve to bring the measured value back to the setpoint.
What is a valve positioner?
In a standard system, the process controller sends a signal directly to the actuator, which moves the valve. This system works, but it can be slow, and actuators always have a certain offset, so they are only accurate within a range.
In applications where changes are made frequently or precision is required, something extra is needed to ensure fast, accurate responses. That something extra is a valve positioner.
A valve positioner is a device that interfaces with the process controller and the actuator, and is connected to the valve stem so it can sense the exact position of the valve. The positioner receives an input signal from the process controller and outputs a signal to the actuator to move the valve.
Read more about how valve positioners work here: Control Valve Actuator Bench Set Requirements
5 top benefits of valve positioners for control valves
Not all applications require valve positioners. But in many applications, valve positioners offer advantages, especially in systems where fluctuations can be disastrous for productivity or quality.
Since valve positioners know the valve&#;s exact position, they provide more precise control than can be achieved by an actuator on its own. In addition, positioners improve accuracy in the lower part of the valve stroke, where errors are more common.
Positioners help control valves respond faster to changes in the process variable, minimizing the amount of time the system is operating above or below the setpoint.
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Varying differential pressure across the valve can indicate instability in the control loop. A positioner is one solution to help stabilize valve position.
A positioner allows you to put distance between the controller and the control valve, as well as to use diaphragm or piston-controlled actuators. You can also switch between direct and reverse control action or change the flow characteristics when necessary. You can even use one controller for two valves (i.e., split ranging).
Friction in the valve stem packing contributes to both hysteresis and deadband, which reduce productivity.
These aren&#;t the only benefits of positioners &#; the value you can gain from them depends on your application and the configuration of your system. To learn how installing positioners helped one oil company keep their system running at peak performance, check out our recent case study: How Trinity EOR Reduced Unplanned Downtime and Improved Plant Performance.
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Automation helps with activities and processes without the need for personnel to physically engage in carrying them out. Automating valves is particularly valuable for controlling flow in piping systems requiring precision control or fail-safe emergency shutoff. A closer examination of the various benefits of using automated valves provides insight into their overall industrial impact, improved output control, and increased safety in manufacturing and production.
The use of automated valve actuators affects several aspects of manufacturing and different forms of processing, which might include hazardous materials, oil and gas, chemicals, food and beverage, and others. Operating valves manually poses a series of risks:
Automated valve actuators provide operators with a more efficient, streamlined control of piping system flows facilitating more accurate costs per unit.
Improved output control using automated valves helps to cut costs related to product waste. Automated valves do not depend on an operator, which allows them to continue to monitor and adjust flow through a system without interruption.
Paired with battery backup systems providing an emergency power supply, they can continue to produce even during power outage events or at least safely end the current process until utility power is restored. Valve automation allows operators to set optimal operating positions, allowing for flow adjustments and monitoring with limited operator involvement. Automated valves also help maintain the safest possible operating levels when dealing with potentially dangerous materials and environmental factors.
Adding to operator safety, actuator valves help to control consistent operating levels and maintain safety in environments where extreme temperatures, pressure levels, noxious fumes, flammable elements, or other circumstances have the potential to create catastrophic failures. In emergencies, automated valve actuators return to fail-safe positions, preventing accidents, environmental hazards, damaged to equipment or structures, and other devastating consequences.
This type of valve also allows for remote access of valves that might be difficult or impossible to reach safely in order to manually return them to a safe position.
A number of automated valve options, including fail-safe actuators, are available from Indelac Controls, Inc. Our custom mounting kits give us the capability to automate any type of valve or damper.
The products we engineer meet CSA NEMA-7 standards and are manufactured in the United States to ensure optimal quality control during design and production. Our team of experts can help clients identify of worn or damaged automated valves or valve components and assist with replacement operations. As a U.S.-based company, we can also provide expedited shipping anywhere in the country.
Automation has an impact on a wide range of manufacturing operations. It is especially beneficial when applied to valve actuation in processing facilities. Among the benefits of valve automation are greater cost-effective production through the reduction of waste, optimized output control requiring limited operator interaction, and increased safety of systems with the potential to produce catastrophic events in emergency situations.
Contact us or request a quote for more information about our automated valves and related products and services.
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