What is a Control valve Positioner?
In older style systems, a Process Controller would send a signal directly to the diaphragm 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 is a Control Valve Positioner.
A Control 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.
How does a Control Valve Positioner work?
Positioners are devices that contribute to the Control valve in positioning the actuator with the help of a control signal. They respond according to the input signal they receive pneumatically or Control valves to a specified position. A Control Valve Positioner is an interpreter between the control valve assembly and the control system that translates the output signal from the control system. It adjusts the air to the actuator which then moves the valve to the desired position requested by the control system.
Therefore, the Positioner will fight against any other forces acting on the valve stem to reach crisp and accurate stem positioning based on the command signal. A properly functioning positioner ensures the control valve will be well-behaved and obedient to the command signal.
What are the different types of Control Valve Positioners?
- Digital Positioners - The MASCOT 3S MP100 high performance digital positioner accurately controls valve stroke according to an input signal of 4-20mA, which is an input from the controller.
- Analogue Positioners - MASCOT 3S XP100 positioners are single or double-acting, force-balanced instruments that provide fast, sensitive and accurate positioning of cylinder and diaphragm actuators.
What are the top benefits of a Control valve Positioner?
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. The top benefits of positioners include:
- More accurate control. 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.
- Faster control. 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.
- Consistent valve position, even with varying pressures. Varying differential pressure across the valve can indicate instability in the control loop. A positioner is one solution to help stabilize valve position.
- More flexible configurations and functions. 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).
- Minimal effects of friction, which causes hysteresis and dead band. Friction in the valve stem packing contributes to both hysteresis and dead band, 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.
How do you choose a Control Valve Positioner?
If you need help deciding which kind of positioner you need, get in touch with our engineers today and we can help you decide.
MASCOT Industrial engineers have over 100 years of combined experience in providing high quality equipment to the Global Continuous Process Control Industry. Our core products and services include control valves, choke valves, actuated and commodity valves, and associated equipment for both standard and severe service applications.
MASCOT’s Engineering & Manufacturing expertise allows us to provide tailored solutions to our customers’ needs with timeliness and accuracy no matter the process. We aim to exceed our expectations with Better Value highly engineered products, faster delivery (-times) on any process, offering support from first contact through to after-sales and beyond.
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