Valve set point positioners that automatically monitor and adjust as needed can be highly effective. These devices provide precise diagnostic capabilities and monitor and record valve actuators’ data.
Maintenance planning and proactive asset management are necessities in the factory’s quest for optimal efficiency and production, leading to a heightened focus on preventative maintenance.
Since pneumatic globe-type control valves are so frequently used in the industrial process loop, they would also benefit from such attention. After all, they are essential to the success of many endeavors. The costs associated with downtime, productivity losses, inefficiency, and dangerous occurrences caused by malfunctioning control valves can be quite high.
Valve set point positioners that automatically monitor and adjust as needed can be highly effective. These devices provide precise diagnostic capabilities and monitoring and recording data from valve actuators. Plant performance and efficiency can be increased with integrated digital connectivity equipment for increased visibility and control over productive assets.
What Is The Valve Positioner?
A valve positioner, a proportional controller, is used to fine-tune actuator output in response to control system input and valve stem position feedback. When used with pneumatic actuators, pneumatic and electropneumetic positioners allow unlimited valve positioning and/or increased force.
Types of Positioners
Electropneumetic, pneumatic, and double-acting rotary valve positioners are the three most popular types.
Pneumatic Valve Positioner:
The relay supply valve and the fixed limitation are supplied with supply pressure. When the flapper is not in place to restrict the nozzle’s diameter, air might flow out quicker than it is being supplied since the restriction orifice’s diameter is less.
The bellows open, and the beam is moved in response to an increased input signal. The beam controls the flapper’s rotation and nozzle diameter. As the pressure in the nozzle rises, the relay diaphragm assembly shifts, allowing supply to flow through the opening. The diaphragm actuator’s output pressure rises, causing the actuator stem to descend.
The rotation of the stem is transmitted to the beam by a cam that makes the flapper angle away from the nozzle. The pressure at the nozzle drops, and the supply valve on the relay switches off to prevent further pressure increases in the output. At a stronger input signal and a slightly altered flapper position, the positioner has again reached equilibrium.
The beam is shifted, and the flapper has pivoted away from the nozzle as the bellows contract in response to a weaker input signal. A reduction in nozzle pressure and exhaust pressure, as well as the opening of the exhaust port in the relay, relieves pressure on the diaphragm casing, allowing the actuator stem to rise.
Like the pneumatic positioner before it, the electropneumetic positioners takes an electrical input signal instead of a pneumatic one. The bellows receive their pneumatic pressure from this current. In all other respects, this positioner operates similarly to its pneumatic counterpart.
The positioners can be switched between direct and reverse actions independently. Adjusting the cam can adjust the valve’s performance from linear to equal percentage or fast opening.
Electro-Pneumatic Positioner Characteristics
- The position of a pneumatic actuator can be adjusted using an electrical signal using the Electropneumetic Positioner.
- To operate valves, dampers, and other pneumatic devices, it takes an electrical input from a control system and transforms it into a pneumatic signal for the actuator.
- Because of this, the position of the actuator may be precisely controlled, which helps boost the system’s efficiency and effectiveness.
- The ElectroPneumetic Positioner can be used in industrial facilities’ various HVAC, power, and process control systems.
- It’s a dependable option for managing pneumatic actuators because it’s long-lasting and straightforward to set up.
- Low-priced and simple to incorporate into preexisting infrastructure.
How Electropneumetic Positioner Works
- Integrated circuit and microcontroller motherboard
- Display and button-equipped control panel
- Constantly-present piezoelectric valve assembly
- The double-acting positioner includes a valve assembly as a spare part.
- Add-on IC for the SIPART PS2 Joystick
- A three-alarm, one-binary-input alarm module
- A mechanical or electrical SIA (slot initiator alarm) module
- Modular restricting switch
- Piston-powered, one-way pneumatic actuator
- Double-acting pneumatic actuator (without a spring)
Double-Acting Rotary Valve Positioner:
An input signal from the controller is processed by the positioner and sent to cavity A of the input module as signal pressure. The addition beam experiences a downward pull as the input signal pressure rises and rotates anticlockwise. As a result, the fin is shifted toward the nozzle, where its pressure is increased. Relay B boosts the pressure in the top cylinder as the beam rotates clockwise in response to increased nozzle pressure. Relay A releases pressure in the lower cylinder of the actuator.
The rotary actuator shaft then rotates clockwise, causing the actuator rod to lengthen. As a result, the feedback lever will rotate clockwise, increasing the range spring’s tension on the summing beam.
This force keeps growing until the summing beam’s twisting moments are at equilibrium, counteracting the input signal’s increasing pressure and pulling the beam down. The valve shaft is now in the ideal position for the input signal.
Positioners are used on control valves for a variety of purposes.
- Pneumatic-spring diaphragm actuators benefit from positioners since they may operate with greater supply pressures.
- Improves linearity of actuator performance by reducing deadband and hysteresis.
- Allows for precise stem alignment by encouraging feedback on where the stem is placed.
- The positioner improves the resolution of the stem’s position by using higher supply pressure and higher spring rates.
- When the actuator’s input signal is 0%, this setting provides no loading pressure. Having the lower bench set wind-in available enables the actuator, which relies on air to open and fail close, to generate the required stopping power.
- Control valve life cycle and overall maintenance depend on performance diagnostic maintenance (PDM), which digital positioners with diagnostics can help.
While I acknowledge that not all digital, electropneumetic positioner, or pneumatic positioners are created equal, some form of the positioner is preferable to none.
Before installing a positioner on a valve, it’s important to consult with your control valve expert or your local business partner who supplies your valves. They can advise you on the best positioners to use and how to install them for maximum control valve efficiency.