A positioner for a control valve is used to adjust a valve’s position based on a desired setpoint for a process variable, whether it be pressure, temperature, or flow. Types of valve positioners include pneumatic, electro-pneumatic, and digital.
In this post, we’ll look at the basics of valve positioners and an overview of these three types.
Producers typically install valve positioners on the yolk or top casing of a pneumatic actuator for linear control valves. On rotary control valves, the valve positioner is installed in line with the valve and actuator stems on top of the actuator or on the side of the actuator. Installation depends on what type of actuator one uses. Affixing the positioner to the actuators allows the positioner to measure the stem travel (linear valves) or degree of rotation (rotary valves). This also changes the position of the valve as required based on the input signal from the instrument controller.
When the process variable differs from the desired setpoint, the instrument controller sends an electrical or pneumatic signal to the positioner. This varies its pneumatic output to the actuator to move the valve open or closed accordingly. This occurs until the process variable reaches the desired setpoint.
Types of Positioner for a Control Valve
There are three primary types of positioners:
- Pneumatic positioners receive a pneumatic signal (typically 3-15 or 6-30 psi) from a controller. They then send a pneumatic signal to the valve actuator.
- Electro-pneumatic positioners receive an electric signal (typically 4-20mA or 0-10 VDC) from a controller. They then send a pneumatic signal to the valve actuator. Analog valve positioners may also be referred to as “analog positioners.” This is because the electrical input to the positioner is an analog signal.
- Digital positioners receive an electric signal (typically 4-20mA, HART, PROFIBUS, or Foundation Fieldbus) from a controller. They then send a pneumatic signal to the valve actuator. The electrical input to a digital positioner can be a digital signal for these positioners. This digital signal allows more advanced capabilities for the user. Some refer to digital valve positioners as “smart positioners.”
The PMV D3 from Flowserve is a digital valve positioner with an exceptional set of features and benefits. It’s extremely simple to use due to five configuration buttons and a large, clear graphic display. The zero-bleed pneumatic relay produces operational cost savings due to the unit’s very low air consumption. Optional plug-in modules offer limit switches (mechanical, proximity and P+F inductive), 4–20 mA feedback and alarm with output function. Communication options include HART®, Profibus PA and DP, Foundation Fieldbus and Wireless ISA100 (see opposite). Advanced valve diagnostics including functionality for running scheduled or manual partial strokes (PST) is available with the optional ValveSight package.
Installation is simple and quick with split spindle design, a friction coupling for the feedback sensor and a wide range of mounting kits designed to fit the majority of actuators on the market. The D3 is not orientation sensitive and mounts on both rotary and linear actuators.
The D3 is available in a standard version an intrinsically safe version and an Explosion proof version for installation in hazardous areas.
Digital valve positioners help simplify safety life cycle phases within your facility.
The PMV P5 and EP5 positioners are fast and accurate analog valve positioner. They available in pneumatic (P5) or electropneumatic (EP5) configurations. Choose from explosion-proof (EP5-EX), fail freeze (EP5-FS) and intrinsically safe (EP5-IS) options.
The EP5/P5 Positioners offer
- Enhanced performance from high-gain, high-capacity spool valve assembly, providing very quick and accurate actuator and valve response plus simple commissioning with non-interactive, zero-span adjustment
- Longer service life assured by robust, simple design, delivering maximum reliability in all environments with intrinsically safe and explosion-proof versions
- Versatility from compact, modular design, allowing for simple addition of I/P converters and/or an F5 feedback unit, low-bleed, tufram, spindle shafts, cams; suitable for single- or double-acting applications
Trust Jeff Morris Limited for All your Valves and Actuation and Positioner needs
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