As the ultimate control unit in most process control systems and automation systems. Pneumatic actuator valves are part of a complex-in-a-system system where valve locating valves can be an indispensable ingredient.
Pneumatic actuator valve body, including bonnet and piping inlet and outlet.
The trim valves, plugs, stem, cage, retainers and discs, are used to control the flow through the body valve.
Transmission, used to supply power to move the valve body or shaft.
Locators, used to control valve position and provide linearity.
To answer this question, we have to answer some of the following questions: “Is there a diagnosis required on the control valve? The seriousness and variability is a problem? Is the position of the valve in the field Long distance from I / P or pneumatic actuator control? ”
If the answer to any question is yes, the positioner is encouraged. Locators have some performance-related features. And can significantly improve the entire pneumatic actuator valve that responds to process setpoints and load changes.
One of the biggest problems of process control is the precise positioning of the valve body (sliding body) or shaft (rotation) during operation.
The function of the actuator is to move the valve body. Or drive shaft to the predetermined position that the controller (DCS or local controller) requires. The controller can control the valve position without the locator. However, the actuator is sometimes inaccurate and depends on many external influences including dynamic stabilization (negative gradient). Upstream rhythm from the pump and change of flow patterns due to the shape pipe type.
The actuators are initially linear, but over time the springs can be degraded. And the effects of the delay and the dead circuit will cause the actuator to operate non-linearly. This can affect the dynamic range of the actuator, reducing sensitivity and resolution. This positioner corrects nonlinearities by increasing the air pressure on the diaphragm to reach the desired position of the body through feedback assembly.
Without feedback, the actuator can not accurately determine the position of the valve. This is worth repeating because the valve actuator is regulating the flow through the valve. Positioning the valve correctly will control the flow more accurately.
As with most of today’s control valves, the type and positioning method is reflected in the choice of starter type. Such as the sliding body or rotary actuator. Most pneumatic actuator, pneumatic actuator and digital pneumatic actuator positioning devices are capable of producing compressed air outputs ranging from 0 to 150 psig. This needs to be considered when choosing the type and style of positioner to use for a particular application.
Providing the boost to the control signal with higher pressure (higher supply pressure) produces higher force to the valve body through the actuator. While the volume boost function provides the required volume for the valve body. The volume of the actuator leads to higher reaction rates (pressure and exhaust emissions).
Provides travel feedback of the pneumatic actuator valve body for precise positioning.
Linear actuator of actuator stroke.
Provides 0 psig loading pressure to the actuator when the zero percentage signal is input to the locator.
The last function is of special importance because the closing control valve is related to the loading pressure of the actuator. This is true with reversing actuators, such as spring diaphragm, air to open, no self-closing gearbox. Since spring is the closing force, the amount of force needed to close the valve is equal to the lower bench multiplied by the effective area of the actuator.
The spring force is wrapped on the actuator to provide this force and this is usually referred to as the lower band. As any air pressure acting on the actuator will decrease from the spring force. It will normally reduce the downward pressure of the load to increase the spring’s closing force in the reversing drive.
Digital positioners offer more precision. Besides providing the previously mentioned attributes of the pneumatic actuator locator, digital positioners can provide online diagnostics. This is extremely useful with product data management and reliability issues when solving problems related to control valves that constantly appear in industrial applications.
The accuracy of the positioning device is excellent, with a resolution of up to 15,000 times. With new magnetic patches on some models. The measurement response is non-contact-free, not affected by vibration and can be measured to an accuracy of 0.004 inches.
Digital positioning is also adjustable, integrated and adjustable. This makes them easier to deal with the various dynamics of the actuators involved. With some models, the setup wizard will set these parameters in a reasonable manner, providing the exact structural information given during the setup.
Running a valve on the valve before use is a good idea. In this way, you have a basic diagnosis for later reference if. And when, you have problems with the control capability of the valve package. In most cases, the information provided by the DVCs is graphical and numeric. With some training, users may find minor problems like wearing hats, worn or broken, leaking membranes and many others – before they become big problems.
The reason for using the positioner on the control valve in most applications includes:
The positions that generate the transmission coefficient for the pneumatic actuator diaphragm actuator by allowing higher supply pressure.
Linearizes the actuator performance by reducing the deadband and hysteresis effects of the actuator.
Provide positive pole position feedback to pinpoint the exact position of the origin.
Increase root resolution by using higher supply pressure and higher springs due to positioning of the locator.
Provides 0 psig load pressure to the 0% input signal of the actuator. This helps the actuator, on the open air, does not close, to use the lower bench put the wind to provide the force needed off.
Digital positioning with diagnostics can help support performance maintenance (PDM) maintenance efforts that are important for controlling the valve life cycle and for maintaining the entire control valve.
While all positioners, pneumatic actuator, pneumatic actuator or digital are not equal, under me any positioner is better than the positioner.
Any decision to use a valve seat location will be made with the valve specialist or your local business partner providing your control valve. They can advise you on the types of correct positioners and important installation techniques for optimizing control valves.