Flow-Tech: Industrial Control Valve Basics

Summary

This video explains the workings of control valve actuators, which regulate fluid flow by varying the orifice size in a valve. The control valve has two main components: the valve body, which houses the fluid connections and restrictor, and the valve actuator, which moves the restrictor to adjust flow. Three types of actuators are discussed: spring and diaphragm, solenoid, and motor-based. Each method controls the valve differently, using pneumatic signals, magnetic fields, or motorized movements, to manage fluid flow for various applications, including both on/off and proportional control modes.

Takeaways

• 🔧 Control valve actuators regulate fluid flow in a pipe by varying the orifice size.
• 🏗️ Control valves have two major components: the valve body and the valve actuator.
• 💧 The valve body contains the fluid connections and the movable restrictor that controls fluid flow.
• ⚙️ The valve actuator moves the restrictor to adjust the flow of fluid.
• 🔩 There are three types of actuators used in control valves: spring and diaphragm, solenoid, and motor.
• 🌬️ Spring and diaphragm actuators use a pneumatic signal to exert pressure on the diaphragm, which moves the restrictor.
• 📏 The 3-15 psi pneumatic signal controls the restrictor’s position and the flow rate through the valve.
• ⚡ Solenoid actuators use current to generate a magnetic field, moving the valve to fully open or fully closed positions.
• 🔄 Motor actuators provide proportional control using a gear motor and a servo amplifier to adjust the valve's position.
• 🔙 Feedback mechanisms, like wiper arms, help the motor actuator maintain precise positioning by monitoring signals.

Q & A

What are the two main components of a control valve?

The two main components of a control valve are the valve body and the valve actuator.

What role does the valve body play in a control valve?

The valve body provides the fluid connections and houses a movable restrictor, consisting of a valve stem and plug, that varies the flow of fluid.

How does the valve actuator affect fluid flow in a control valve?

The valve actuator physically moves the restrictor, adjusting the orifice size to control the flow of fluid through the valve.

What are the three types of actuators used in control valves?

The three types of actuators used in control valves are spring and diaphragm, solenoid, and motor actuators.

How does the spring and diaphragm actuator operate?

A spring and diaphragm actuator uses a 15 psi pneumatic signal to apply pressure on the diaphragm, which exerts a downward force on the spring, moving the valve stem and plug to adjust fluid flow.

What happens in a spring and diaphragm actuator when no air pressure is applied?

With no air pressure, the spring pushes the restrictor upward, causing the valve to act as a normally open control valve.

What is the purpose of a current-to-pressure transducer in a spring and diaphragm actuator?

A current-to-pressure transducer is used to provide a 3 to 15 psi signal to the diaphragm, allowing for proportional control of the valve's flow based on the applied pressure.

How does a solenoid actuator control the valve?

A solenoid actuator uses a magnetic field generated by current applied to a coil, which moves the plunger to open or close the valve for on/off control.

How is variable valve positioning achieved using a motor actuator?

Variable valve positioning is achieved using a motor actuator by utilizing a gear motor and a servo amplifier. The servo amplifier provides a DC control signal to adjust the valve position, with feedback from a wiper arm that monitors the valve's position.

What is the role of the servo amplifier in motor-operated valves?

The servo amplifier drives the motor until the control signal is equal to the feedback signal from the valve position, ensuring precise positioning.

Outlines

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🔧 Introduction to Control Valve Actuators

This section introduces control valve actuators, which manage the flow of fluid through a pipe by adjusting the orifice size. The control valve consists of two main components: the valve body and the valve actuator. The valve body includes fluid connections and a movable restrictor (valve stem and plug) that varies the flow, while the actuator physically moves the restrictor to control fluid flow. Various actuator types include spring and diaphragm, solenoid, and motor-driven actuators.

🌀 Spring and Diaphragm Actuator Functionality

Here, the spring and diaphragm actuator is described. It operates by using a 15 psi pneumatic signal applied to a diaphragm, which moves against a spring to control the valve restrictor. The diaphragm moves until it balances the spring force, which then stops motion as the valve plug meets the seat. In this design, when no air pressure is applied, the spring holds the valve in a normally open position.

🔄 Current-to-Pressure Transducer for Valve Control

This paragraph explains how a current-to-pressure transducer is used to vary the valve's restrictor position and fluid flow. The transducer converts a 3-15 psi signal to control the diaphragm and thus the valve. For example, at 3 psi, the valve remains fully open, at 15 psi, it is fully closed, and intermediate pressures adjust the flow proportionally. A pressure of 9 psi sets the valve to 50% of its operating range.

⚡ Solenoid Actuated On/Off Valve Control

This section discusses solenoid actuation for on/off valve control. Applying current to the solenoid coil generates a magnetic field that pushes the plunger downwards against the return spring, closing the valve. When no current is applied, the return spring lifts the plunger to open the valve, maintaining a normally open state.

🔧 Motor-Driven Proportional Control Mode

Motor-driven proportional control actuators use a gear motor to control the valve's position. A servo amplifier sends a DC control signal to position the valve based on feedback from a wiper arm attached to the valve stem. This feedback ensures accurate positioning by comparing the control signal with the feedback, allowing the motor to adjust the valve until the two signals match.

Keywords

💡Control Valve Actuator

A control valve actuator is a device that adjusts the flow of fluid in a pipe by varying the size of the orifice. In the video, it is described as the mechanism that physically moves the restrictor (the valve stem and plug) to regulate the fluid flow. Actuators can be of different types, such as spring and diaphragm, solenoid, or motor-driven.

💡Valve Body

The valve body is a key component of a control valve, providing the fluid connections and housing the restrictor. In the video, the valve body contains a movable valve stem and plug that interact with the fluid to change its flow. It's critical for directing the fluid flow through the system.

💡Restrictor

The restrictor in a control valve consists of a valve stem and plug, and its position determines the amount of fluid flowing through the valve. By moving the restrictor, the actuator can adjust the fluid flow, as explained in the video. When the restrictor is fully closed, the fluid stops, and when it is open, fluid passes through.

💡Spring and Diaphragm Actuator

This type of actuator uses a spring and diaphragm to move the valve stem and plug. In the video, it is detailed that pneumatic pressure is applied to the diaphragm, causing it to move against the spring and adjust the valve. This actuator type enables precise control of the fluid flow based on the pressure signal.

💡Pneumatic Signal

A pneumatic signal is the air pressure input, typically between 3 to 15 psi, that controls the movement of the diaphragm in a spring and diaphragm actuator. In the video, a 15 psi signal causes the restrictor to close, while a 3 psi signal keeps the valve open. Intermediate pressures adjust the valve's position proportionally.

💡Current-to-Pressure Transducer

This device converts an electrical current into a pneumatic signal (3 to 15 psi) that controls the actuator. In the video, the transducer helps in modulating the valve's position by providing the appropriate pneumatic pressure to the diaphragm for precise flow control.

💡Solenoid

A solenoid is an electromagnetic device used for on/off control of a valve. In the video, it is explained that applying current to the coil creates a magnetic field that moves the plunger to close or open the valve. This actuator allows for binary (fully open or closed) valve positions, useful for simple flow control applications.

💡Proportional Control

Proportional control refers to adjusting the valve's position incrementally rather than fully open or closed, based on the control signal. In the video, a motor-driven actuator uses proportional control to vary the fluid flow by positioning the valve according to a DC control signal, providing a more precise fluid regulation method.

💡Servo Amplifier

A servo amplifier is a device that processes control signals and drives a motor to adjust the valve's position. In the video, it is used in motor-driven actuators to ensure the valve moves to the desired position by comparing the control signal to feedback from the valve stem's position.

💡Feedback Signal

A feedback signal provides information about the current position of the valve stem, helping to adjust the control signal to match the desired valve position. The video explains that a wiper arm attached to the valve stem sends this signal to the servo amplifier, ensuring accurate positioning and flow control.

Highlights

Control valve actuators manage fluid flow in pipes by adjusting the orifice size.

Control valves are made of two key components: the valve body and the valve actuator.

The valve body provides fluid connections and contains a movable restrictor that varies flow.

The valve actuator moves the restrictor, controlling the fluid flow through the valve.

Three main actuator types are used: spring and diaphragm, solenoid, and motor.

The spring and diaphragm actuator uses a pneumatic signal to move the valve stem and plug.

A 15 psi pneumatic signal pushes the diaphragm, exerting force to move the restrictor.

The spring returns the restrictor to its normal position, ensuring the valve remains normally open without air pressure.

A current-to-pressure transducer provides a 3 to 15 psi signal to control flow positions.

At 9 psi, the spring moves the valve stem to 50% of its operational range.

For on/off control, solenoids fully open or close the valve by applying current to generate a magnetic field.

The motor actuator allows for proportional control of the valve’s position.

A servo amplifier controls the motor, driving the valve to the desired position.

Feedback control ensures the valve’s position is accurate using a wiper arm attached to the valve stem.

The servo amplifier continues to adjust the motor until the control signal matches the feedback signal.

Transcripts

control valve actuators control fluid in

a pipe by varying the orifice size

through which the fluid flows

control valves contain two major

components the valve body and the valve

actuator

the valve body provides the fluid

connections and a movable restrictor

comprised of a valve stem and plug that

is in contact with the fluid that varies

the flow

the valve actuator is the component that

physically moves the restrictor to vary

the fluid flow

three actuator types are used in control

valves and they include spring and

diaphragm solenoid and motor as the name

suggests the spring and diaphragm

actuator uses a spring and a diaphragm

to move the valve stem and plug

a 15 psi pneumatic signal enters the

housing at the top of the actuator as

pressure is exerted on the diaphragm a

downward force is applied against the

spring which moves the restrictor the

diaphragm moves until it creates an

equal but opposing force against the

spring at which time the motion stops as

the plug meets the valve seat

with no air pressure the restrictor is

pushed upward by the spring to act as a

normally open control valve

to vary the position of the restrictor

and flow through the valve a current to

pressure transducer can be used to

provide a three to 15 psi signal to the

diaphragm

at 3 psi the valve is maintained open

and at 15 psi the valve is maintained

closed pressures between the 3 to 15 psi

range proportionally change the flow of

the valve for example a pressure of 9

psi applied to the diaphragm moves the

spring and valve stem to 50% of

operating range

for on/off control of the valve a

solenoid is used to actuate the valve to

a fully closed or fully open position

applying current to the coil generates a

magnetic field that moves the plunger

downward against the return spring

with zero current applied to the coil

the spring pulls the plunger upwards to

the fully open position for a normally

open state control valve another method

for variable valve positioning uses a

motor and is referred to as proportional

control mode using a gear motor attached

to the valve stem a servo amplifier

provides a DC control signal that moves

the valve to the desired position

feedback is achieved with a wiper arm

attached to the valve stem that sends a

signal back to the servo amplifier where

the position is monitored the servo

amplifier drives the motor until the

control signal is equal to the feedback

signal