While control valves keep critical processes flowing in every major industry—from metals and mining to aerospace and defense—they rarely do it alone. This is especially true if you’re an engineer looking to maximize efficiency with exact control of your flow or process variable.
In our “Control Valves 101” content series, we’ve already explained the role of **actuators** in changing the valve position. But you need a control valve positioner to optimize their movement accuracy and the valve position.
In this blog post, you’ll learn what a valve positioner does, the two main types of valve positioner, and critical design choices.
Every automated control valve has an actuator—a device mounted on the valve that creates the motion to change the valve’s position. But, an actuator acting alone can’t control process variables with great precision, which you need for a fully efficient process control system. It requires a valve positioner.
A valve positioner is a signal-receiving device that attaches to an actuator. The signal comes from a controller. The controller measures and controls a process variable in the process control system, such as temperature, pressure, or flow rate.
The valve positioner constantly receives a signal from the controller. This signal tells the valve positioner the metric that the process variable should meet (known as a set point) and compares it to the actual process variable.
Let’s say the valve positioner finds that the process variable has deviated from the set point. In response, it sends the necessary power to move the actuator until the valve reaches the correct position. This causes the process variable to meet the set point again.
The signal comparison-correction process is constant, keeping the process variable in check without human monitoring or intervention.
There are two main types of control valve positioners, which are determined by the kind of signal they receive—pneumatic or digital.
Pneumatic positioners receive and convert a pneumatic signal—gas or air pressure in a pipe—to move an actuator. As such, it doesn’t require an electric power supply.
Typically, you would use a pneumatic positioner if:
Digital positioners receive and convert an electronic signal to move an actuator, so they require an electric power supply.
While all positioners allow more precise control of the valve position, digital positioners have extra benefits. These include:
Due to their electronic components and electric power supply, some applications or environments might not seem suitable for digital positioners. But valve positioner housing can change that.
A valve positioner’s design, including its external housing, helps it function efficiently and protects it from damage and deterioration. But, positioner design can also mitigate the risks associated with digital positioners. There are three main types of valve positioner design, which are:
A general purpose valve positioner is all you need for a non-hazardous process control environment. Its housing protects the valve positioner components from dust or water, avoiding unplanned maintenance and prolonging their lifespan.
Manufacturers like Trimteck engineer intrinsically safe valve positioners to limit their thermal or electrical energy. This includes simpler circuitry, temperature control, and high dust resistance, meaning they cannot catch fire and trigger an explosion in an explosive atmosphere.
Explosion-proof valve positioners do not need the same design precautions as intrinsically safe valve positioners because they have an explosion-proof housing. It means that, even if the internal components catch fire, the flame and gas can’t escape to ignite the external atmosphere.
The right valve positioner can really move the needle on your process efficiency targets. But, to do that, it needs a control valve and an actuator that can match its capabilities.
At Trimteck, our expert Applications Engineers will help you specify the optimal custom solution for your unique process control system. They’ll factor your system requirements into every decision, from the control valve trim to the actuators and positioners. Share your specifications with us online to get your tailored quote.