How Do Control Valve Actuators Work?

Summary

This video explains the function and components of control valve actuators, which regulate fluid flow through pipes by adjusting the orifice size. It covers three actuator types: spring and diaphragm, solenoid, and motor. The spring and diaphragm actuator uses pneumatic pressure to adjust a valve stem and plug, while the solenoid actuator uses magnetic fields for on/off control. The motor actuator is used for proportional control, adjusting the valve's position based on feedback signals. The video provides a comprehensive overview of how these actuators work to manage fluid flow in various control systems.

Takeaways

• 😀 Control valve actuators regulate fluid flow by adjusting the size of the orifice in a pipe.
• 😀 A control valve consists of two major components: the valve body and the valve actuator.
• 😀 The valve body contains a movable restrictor (valve stem and plug) that interacts with the fluid to vary flow.
• 😀 The actuator moves the restrictor to control the flow of fluid through the valve.
• 😀 There are three main actuator types: spring and diaphragm, solenoid, and motor actuators.
• 😀 Spring and diaphragm actuators use a pneumatic signal to apply pressure on a diaphragm, moving the valve stem and plug.
• 😀 In a spring and diaphragm actuator, pressures between 3 to 15 PSI proportionally change the valve’s position and fluid flow.
• 😀 Solenoid actuators use a magnetic field generated by a coil to move a plunger, fully opening or closing the valve.
• 😀 With solenoid actuators, when no current is applied, the valve remains in the fully open position due to the return spring.
• 😀 Motor actuators allow for proportional control, using a gear motor and servo amplifier for precise positioning of the valve.
• 😀 Feedback from a wiper arm attached to the valve stem helps monitor the position and adjust the motor until the desired position is reached.

Q & A

What are the two major components of a control valve?

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

How does a control valve regulate fluid flow?

A control valve regulates fluid flow by varying the orifice size through which the fluid flows, using a movable restrictor comprised of a valve stem and plug.

What role does the actuator play in a control valve?

The actuator physically moves the restrictor (valve stem and plug) to vary the fluid flow through the valve.

How does the spring and diaphragm actuator work?

In a spring and diaphragm actuator, a pneumatic signal enters the housing and exerts pressure on the diaphragm, which moves a spring and restrictor to vary the fluid flow.

What happens when the diaphragm actuator receives no air pressure?

When no air pressure is applied, the restrictor is pushed upward by the spring, maintaining a normally open control valve state.

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

The current-to-pressure transducer provides a 3 to 15 psi signal to the diaphragm, controlling the valve position. A 3 psi signal keeps the valve open, and a 15 psi signal keeps it closed.

How does the solenoid actuator operate in a control valve?

A solenoid actuator uses an electrical current to generate a magnetic field, which moves a plunger against a return spring. When no current is applied, the spring pulls the plunger upward, keeping the valve fully open.

What is the function of the motor actuator in a control valve?

The motor actuator uses a gear motor attached to the valve stem and is controlled by a DC signal from a servo amplifier. The motor adjusts the valve position based on feedback to achieve proportional control.

What is feedback in a motor actuator, and how is it achieved?

Feedback in a motor actuator is achieved using a wiper arm attached to the valve stem, which sends position data back to the servo amplifier to ensure the valve is at the correct position.

What is the significance of the feedback signal in a motor-controlled valve?

The feedback signal in a motor-controlled valve ensures that the valve is positioned correctly by comparing the control signal with the actual valve position, and adjusting the motor until they match.