How Pneumatic Control Valve Works | Control Valve Actuator Types | Control Valve Positioner Types

Summary

This video script delves into the world of control valves, essential in regulating industrial processes like temperature and pressure. It introduces the components of a control valve, including the body, bonnet, plug, actuator, and positioner. The video explains how a positioner translates PLC commands into actuator movements, using an example of controlling liquid temperature in a tank. It also covers different types of actuators and positioners, highlighting the benefits of digital positioners for precise control and easy calibration through digital communication protocols.

Takeaways

• 🔄 **Control Systems Overview**: The script explains the necessity of a control system, including a PLC (Programmable Logic Controller), sensors, transmitters, and a final control element like a pump or valve, to manage process parameters such as temperature and pressure.
• 🛠️ **Role of Control Valves**: Control valves are not just for starting and stopping flow but also for throttling it to achieve specific process goals like regulating temperature or liquid levels.
• 🌡️ **Temperature Control Example**: An example is given where a control valve regulates the temperature of a liquid in a tank by controlling the flow of a heat-generating additive.
• 📡 **PLC and Sensor Integration**: The PLC sends commands to the control valve based on its logic and feedback from temperature sensors, typically using a 4-20mA DC signal.
• 🔧 **Positioner and Actuator Functions**: The positioner acts as an interface between the PLC and the actuator, converting the PLC's signal into a form that the actuator can use to move the valve stem.
• 💬 **Signal Conversion Process**: The positioner contains an I to P Transducer that converts the electrical current signal from the PLC into a pneumatic signal that the actuator can understand.
• 🔌 **Electro-Pneumatic Positioners**: These positioners are used with pneumatic actuators and include an I to P Transducer to convert electrical signals to pneumatic pressure.
• 🔄 **Feedback Mechanism**: Both the PLC and the positioner require feedback to ensure the valve is adjusted correctly; the positioner receives mechanical feedback from the control valve.
• 📱 **Digital Positioners**: These use a microprocessor for more accurate control and can communicate with the PLC or DCS using digital protocols, simplifying calibration and allowing for remote feedback.
• 🔑 **Actuator Types**: Actuators are categorized into Pneumatic, Hydraulic, Electric, and Manual, with pneumatic actuators being the most common due to their simplicity and safety.
• ❓ **Engagement Invitation**: The script concludes with an invitation for viewers to ask questions or share experiences with control valves, and to subscribe for more content.

Q & A

What is the primary function of a Programmable Logic Controller (PLC) in a control system?

A PLC is used to control various parameters of a process, such as temperature and pressure, by sending commands to final control elements like pumps, heaters, or control valves.

What are the main components required to send data to a PLC?

Sensors and transmitters are needed to collect data and send it to the PLC for processing and control.

What is a 'Final Control Element' in the context of a control system?

A Final Control Element is a piece of equipment, such as a pump, heater, or control valve, that carries out the commands issued by the PLC.

How do control valves differ from regular valves in terms of their function?

Control valves are not only used to fully start and stop the flow but also to control, adjust, or throttle the flow of a liquid for precise process control, such as temperature or level control.

What is a 'Globe valve' and what are its main parts?

A Globe valve is a common type of control valve that includes the body through which fluid passes, the bonnet that covers the inner parts, the plug that controls the flow, and the actuator that moves the plug.

What is the role of an 'Actuator' in a control valve system?

An Actuator transfers mechanical power to the plug of a control valve using a stem, receiving commands from the Positioner to open or close the valve.

What is the purpose of a 'Positioner' in a control valve system?

A Positioner serves as an interface between the PLC and the Actuator, adjusting the plug's position to open or close the valve precisely according to the PLC's commands.

How does a Positioner convert the PLC's command signal into a signal that the Actuator can understand?

A Positioner contains an 'I to P Transducer' that converts the 4-20mA DC electrical current signal from the PLC into a 3-15PSI pneumatic air pressure signal for the Actuator.

What is the significance of the 'Air supply' input in a Positioner?

The Air supply input provides clean, filtered, and regulated air with sufficient pressure to the Positioner, which, along with a built-in pressure amplifier, enables the conversion of the pneumatic signal into enough force to move the Actuator.

How does a Positioner receive feedback to ensure the valve is opened to the correct percentage?

A Positioner receives mechanical feedback from the control valve, which allows it to adjust the valve stem position precisely to match the command from the PLC.

What are the three main categories of Positioners mentioned in the script?

The three main categories of Positioners are Electro-Pneumatic Positioners (I/P Positioners), Pneumatic Positioners, and Digital Positioners or Digital Valve Controllers.

How do Digital Positioners differ from other types of Positioners?

Digital Positioners use a microprocessor to replace the mechanical position feedback, allowing for more accurate valve position adjustments and the ability to communicate via digital protocols like HART or Fieldbus.

What are the four categories of Actuators mentioned in the script?

The four categories of Actuators are Pneumatic, Hydraulic, Electric, and Manual, each with its own advantages and applications.

How can Digital Positioners improve the calibration process of control valves?

Digital Positioners enable easier calibration of control valves using handheld communicators and digital communication protocols, reducing the need for time-consuming and difficult mechanical adjustments.

Outlines

00:00

🤖 Understanding Control Systems with PLCs and Valves

The first paragraph introduces the concept of control systems, emphasizing the need for a controller like a Programmable Logic Controller (PLC) to manage parameters such as temperature and pressure. Sensors and transmitters are highlighted as essential components that send data to the PLC, with the final control element being responsible for executing the PLC's commands, such as pumps or heaters. The paragraph also introduces the concept of control valves, which are used not only to start or stop flow but also to adjust it, with the example of a globe valve being dissected into its main parts: body, bonnet, plug, actuator, and positioner. The role of the positioner as an interface between the PLC and the actuator is explained, along with the variety of actuator and positioner types that will be explored later in the video.

05:05

🔧 The Mechanics of Positioners and Actuators in Control Valves

The second paragraph delves into the operation of positioners and actuators within control valves, using the example of controlling the temperature of a liquid in a tank by regulating the flow of an additive. The PLC's decision-making process based on its logic and feedback from a temperature sensor is explained, along with how the positioner acts as a translator between the PLC's signal and the actuator's language. The conversion of the 4-20mA electrical current signal to a pneumatic signal is detailed, including the role of the I to P Transducer. The importance of the air supply and the positioner's feedback mechanism for precise valve positioning is also discussed. The paragraph concludes with an overview of the different types of positioners, including Electro-Pneumatic, Pneumatic, and Digital, each with their unique features and applications. Additionally, a brief introduction to the classification of actuators into Pneumatic, Hydraulic, Electric, and Manual is provided, setting the stage for further exploration in the video.

Keywords

💡Control

Control in the context of this video refers to the management of various parameters such as temperature and pressure in a process. It is the overarching theme of the video, which discusses how to achieve precise control over these parameters using different components. For example, the video mentions controlling the temperature of a furnace or the level of liquid in a tank.

💡Programmable Logic Controller (PLC)

A PLC is an industrial digital computer used to control manufacturing processes, machines, or equipment. In the video, it is identified as a necessary component for achieving control over processes, receiving data from sensors and transmitters and sending commands to final control elements.

💡Sensors and Transmitters

Sensors and transmitters are devices that detect and send data to the PLC. They are essential for monitoring the process parameters like temperature and pressure. The video script mentions these devices as a means to send data over to the PLC for further control actions.

💡Final Control Element

The final control element is the equipment that carries out the PLC's commands. Examples given in the video include a pump, a heater, or a control valve. It is the last link in the control chain, executing the actions determined by the PLC.

💡Control Valve

A control valve is a type of valve used not only to start and stop the flow but also to control or adjust the flow of a liquid. The video provides a detailed explanation of how control valves work, particularly in the context of throttling the flow to achieve specific process control objectives.

💡Globe Valve

The globe valve is one of the most common types of control valves. The video script describes its parts, such as the body, bonnet, plug, and actuator, and explains how these components work together to control the flow of fluid.

💡Actuator

An actuator is a device that transfers mechanical power to the plug of a control valve using a stem. It receives commands from a positioner and is responsible for the physical movement that opens or closes the valve. The video script uses the example of a pneumatic actuator to explain this concept.

💡Positioner

A positioner serves as an interface between the PLC and the actuator, ensuring precise adjustment of the valve plug. The video script explains the role of the positioner in converting the PLC's command signal into a form that the actuator can understand and act upon.

💡I to P Transducer

An I to P transducer is a converter unit inside the positioner that changes an electrical current signal into an air pressure signal. The video script describes how this transducer converts the 4-20mA signal from the PLC into a 3-15PSI pneumatic signal for the actuator.

💡Pneumatic Signal

A pneumatic signal is an air pressure signal used to control pneumatic actuators. The video script explains that the positioner converts the electrical signal from the PLC into a pneumatic signal, which is then used to operate the actuator.

💡Digital Positioner

A digital positioner, also known as a digital valve controller, uses a microprocessor to replace the mechanical position feedback. The video script highlights the advantages of digital positioners, such as ease of calibration and the ability to communicate with the valve using digital protocols.

💡Actuator Types

The video script categorizes actuators into four types: pneumatic, hydraulic, electric, and manual. Each type has its specific applications and advantages, and the script explains how they are used in the context of control valves.

Highlights

Importance of control over parameters like temperature and pressure in processes.

Use of Programmable Logic Controllers (PLC) for process control.

Role of sensors and transmitters in sending data to PLC.

Definition and function of a 'Final Control Element' in a control system.

Introduction to control valves and their purpose in throttling the flow of liquids.

Explanation of how control valves can regulate temperature or liquid levels.

Description of a 'Globe valve' and its components.

Function of the 'Actuator' in transferring mechanical power to control the valve.

Role of the 'Positioner' as an interface between PLC and Actuator.

Types of Actuators and Positioners in control systems.

Example of controlling liquid temperature in a tank using a control valve.

How PLC commands are sent and interpreted by the control valve system.

Conversion of PLC signals to pneumatic signals by an electro-pneumatic positioner.

Explanation of the 'I to P Transducer' and its function in signal conversion.

Importance of air supply and pressure amplification in actuator movement.

Mechanical feedback mechanism from the control valve to the Positioner.

Categories of Positioners: Electro-Pneumatic, Pneumatic, and Digital.

Advantages of Digital Positioners and their use of microprocessors.

Communication protocols like HART or Fieldbus for valve control and feedback.

Standalone I/P transducers for less critical accuracy applications.

Classification of Actuators into Pneumatic, Hydraulic, Electric, and Manual types.

Discussion on the use and advantages of Spring-and-Diaphragm actuators.

Invitation for viewer questions and comments on control valve experiences.

Transcripts

We would almost always like to have control over different parameters of the process

like temperature, pressure, level, and so on

To achieve this, obviously, we need a controller

like Programmable Logic Controller or PLC for short

We also need some sensors and transmitters to send data over to PLC

Finally, we need a piece of equipment to carry out the PLC’s commands

which usually called as “Final Control Element”

A Final Control element can be a pump, a heater, a control valve, and so on

If you would like to figure out how control valves exactly work

via an interesting practical example, stay with us to the end of this video

If you like this style of video, subscribe

and click the bell to receive notifications of new videos by Upmation

Very often by “Control Valves” we mean the type of valves

that are used not only to fully start and fully stop the flow

but also to control or adjust or in other words throttle the flow of the liquid

By throttling the flow, we achieve our final purpose that is

for example, controlling the temperature of a furnace

or the level of a liquid inside a tank

You may say how it is possible!

Don’t worry! We are going to talk about it in detail.

Well, this is a “Globe valve”; One of the most common types of control valves

Let’s take a quick look at its different parts

This is the “Body” of the valve that the fluid will pass through it

and this is the Bonnet that is connected to the body and covers its inner parts

We call this part Plug

The plug will control, Stop or Start the flow

by exposing the liquid flowing inside the pipe.

This part here is the “Actuator” that transfers

the mechanical power to the plug using the “Stem”

The Actuator will receive the commands from the Positioner

The main role of the “Positioner” is to be an interface between the PLC

and the Actuator to precisely adjust the plug for being open or closed

There are a variety of Actuator and Positioner types

and we are going to check them all at the end of this video

So, let’s start with an example to understand the operation

of the Positioner and its relation to the PLC and Actuator

In this example, we aim to control the temperature of a liquid within a tank

by regulating the flow of an additive

This additive will generate heat by having a

chemical reaction with the liquid already inside the tank.

Say the PLC decides to send a 50% open command to the control valve

This command is based on two items

First, the PLC logic

and second, the feedback it has received by the temperature sensor

installed on the tank

This command signal often is in the form of a 4-20mA DC electrical current

and is sent from the PLC

The device that receives this signal on the field

is the “Positioner” of the control valve

As we are using a specific type of pneumatic actuator in this example

which needs compressed air to become activated

therefore we chose an electro-pneumatic positioner

Don’t worry about the names at the moment!

In this case, the positioner plays the role of a “translator”

and converts the PLC language to the actuator language!

It means that the Positioner will convert the 4-20mA signal

to an air pressure signal

How it happens?

Well, inside of this Positioner we have a

converter unit which is called “I to P Transducer”

In fact, this transducer converts the 4mA DC current

to a 3PSI air pressure

and the 20mA DC current to a 15PSI air pressure

and of course, they are proportional in the middle range

We call 3-15PSI air pressure as the “Pneumatic Signal”

So with a simple calculation, we understand that

in order for the PLC to open the valve for 50% of its full range

it should send a 12mA signal to the Positioner

Then the Positioner will convert it to a 9PSI signal accordingly

and will send it directly to the actuator

But wait!

It sounds like the 9PSI pressure is not enough to move the actuator

Therefore, we need another input to the Positioner as the “Air supply”

The Air supply input will provide us with a clean, filtered, regulated air

with sufficient pressure, thanks to this filter/regulator device

After all, using the Air supply input and a built-in pressure amplifier

the positioner will be able to convert the 9PSI pressure signal

to sufficient air pressure for moving the actuator to the right amount

Now, we see that the actuator is able to overcome its spring force

and so far so good!

But same as the PLC that requires feedback by the sensor

to decide about the command it is going to send

the Positioner also needs to receive feedback

to precisely position the valve stem and open the valve to 50%.

This feedback is sent by the “control valve” to the Positioner

using a mechanical mechanism

In this way, the Positioner will decide how much pressure

the actuator needs to move the valve stem

In general, Positioners come into three different categories;

First, the “Electro-Pneumatic” Positioners or I/P Positioners

that we already discussed in the example

Second, the “Pneumatic” Positioners, in which their control signal

is a pneumatic signal and they do not need any I/P Transducer modules integrated

The last is “Digital” Positioner or “Digital Valve Controller”

In addition to an “I to P Transducer”

these positioners take advantage of a “Microprocessor”

to fill in the place of the mechanical position feedback.

The input signal or setpoint from the PLC will directly send to the Microprocessor

The valve position feedback which is measured electronically

will also enter the Microprocessor

Comparing these two electronic signals

the Microprocessor is able to adjust the valve position

quite accurately in comparison with the other types of positioners.

Using Digital Positioners, we are able to communicate with the valve

by different types of protocols such as HART or Fieldbus protocols like Profibus

By such digital communications, we can calibrate control valves

way more easily using and-held communicators

without tackling time-consuming and sometimes difficult mechanical adjustments

Besides, we can send some feedbacks from the control valve to the PLC

or DCS via these communication protocols

The last point is that the standalone I/P transducers can control the valve

independently in case that the accuracy is of less importance

Meaning that, they are not integrated into any kind of positioners

and therefore there is no feedback in this case

Now that we’ve got introduced to the positioners

let’s get into the Actuators and their different types

Generally, we can classify the Actuators into four different categories

Pneumatic, Hydraulic, Electric, and Manual

The Pneumatic actuators are the most used kinds of actuators

due to their simple design

fairly low price and of course being Intrinsically Safe

Electric Actuators have an electric motor inside

In the first place, they had been designed for on/off applications

but nowadays some of them are upgraded for continuous control applications

The primary application of them

is in the locations that we don’t access the compressed air

In this video, we learned how a Spring-and-Diaphragm actuator

along with an Electro-Pneumatic Positioner

adjusts the valve in order for the valve

to control the flow of the liquid according to the PLC commands

Well, it’s time to ask us your question

or tell us about your experiences dealing with the control valves in the comments

Again if you like these kinds of videos please subscribe

and tell us which subjects you are most interested in

Thanks for watching!