Put simply, the positioner is an integral part of the fluid flow control system.
A liquid flow control system consists of three basic devices: positioner, control valve and actuator. Vavle is responsible for closing or opening completely, changing the flow of fluid. The actuator is responsible for generating the appropriate force on the valve to control the position of the valve. The positioner is responsible for closing or opening, adjusting the amount of compressed air corresponding to the control signal into the actuator. With the three components above, the flow of fluid is completely controllable.
Positioner is one of the most widely used equipment in basic industrial plants. In factories that use raw materials, fuels such as water, oil, gas. These materials are precisely controlled by the operator, which is an important link in the chain of making many products from simple to complex for human life.
As one of the precision control devices, the control system receives and responds to the signal so that Valve’s location is most accurate.
The valve positioner compares a control signal to the position of the valve actuator and moves the actuator accordingly. They are used with both linear and rotary valves. Valve positioning valve is used when the pressure from 0.2 to 1 bar in the membrane chamber can not cope with friction and high differential pressure.
The positioner is mounted on the yoke of the actuator and is connected to the spindle of the actuator with a feedback arm to monitor the valve position. When a control signal differs from the position of the valve actuator, the positioner will send the power needed to move the actuator until it reaches the correct position. This uses high air supply.
Placements need to be installed if the valve is used in a control application.
There are four basic types of valve positions: pneumatic, electronic, electric, pneumatic and digital. Positioning valves
Compressed air equipment sends and receives compressed air signals. They are safe and can provide a large force to close the valve.
The one- or three-way pneumatic positioner transports air and exhaust from only one side of the one-way valve actuator against one spring.
Two-way or four-way air compressor sends and pulls air from both sides of the actuator.
Electric valve position transmitter and receiver. There are three types of electrical activity: single phase and three phase (AC) and one (DC).
An electronic valve positioning valve converts the current control signal into an equivalent pneumatic signal.
Digital or “smart” devices use microprocessors to locate valve actuators and track and record data. They are very accurate, use less air than similar positioning devices and allow online digital diagnosis.
The performance parameters for the valve locator vary according to the compressed air input range, the maximum supply pressure, the milliampere input range, the dividing band, the operating temperature and the output operation.
The input air pressure range and maximum supply pressure are in units per inch (psi).
The dividing bands usually consist of 4 – 10 mA and 12 – 20 mA. There are two ways of dividing two dimensions, three dimensions and four dimensions.
There are three types of action outputs: direct, reverse, and reverse fields.
Direct acting devices increase the output signal when the input signal is increased.
Reverse devices reduce the output signal when the input signal is increased.
The reversible field products can be switched between direct and reverse operation.
The internal safety valve (IS) locating valve does not generate sparks or other thermal effects that can burn specific gas mixtures. Equipment made of stainless steel is used in corrosive environments or at high temperatures. The valve position should also be accompanied by a valve position indicator suitable for the intended application.
Valve positioning varies on application, features and approval. Some products are designed for automotive, aerospace, marine, medical or military applications. Other products suitable for food or pharmaceutical processing. General purpose devices are usually available.
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, pneumatic and digital pneumatic 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 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 required 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 load pressure to 0 to increase the spring’s closing force in the reversing drive.
General reviews of the valve locator include trademarks from the Canadian Standards Association (CSA) and Underwriters Laboratories (UL), an independent inspection body. Additional standards can be found at the IHS Standards Store.
BS EN 60534-6-1 – Industrial process control valves Part 6: Mounting details for mounting positions to control valves. Part 1: Positioning the linear actuator
IEC 60534-6-2 – This part of IEC 60534 is designed to allow multiple positioning devices, which meet rotary motion, mounted on the actuator of the control valve, either directly or by using a Intermediate installation frame.
Also, at naman-tech we provide E-P Positioner. Typical is the Electro Pneumatic Positioner TS600.
TS600 electro-pneumatic positioner controlvalve stroke in response to input signal of 4-20mA from control panel, DCS, or calibrator.
– Applied to various control valve system.
– Fast response time, durability, and excellent stability.
– Simple zero and span adjustment.
– IP 66 enclosure.
– Easy maintenance due to built-in module type.
– Strong to vibrations and No resonance between 5 – 200 Hz.
– By-pass valve (A/M switch) installed.
– Air connection part is designed for detachability and it can be changed PT/NPT tapping threads in the field easily.
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