Control Valve-Control valve Definition-Diagram-working Principle-Symbols-Types-Parts

A control valve is a device that controls, mixes, or closes the process temperature, pressure, flow, etc. It is called a control valve. Or process line variable restriction is called control valve. There are two main and major types of control valves.

Control Valve

A control valve is a device that controls, mixes, or closes the process temperature, pressure, flow, etc. It is called a control valve. Or process line variable restriction is called control valve. There are two main and major types of control valves.

  1. Linear Motion Control Valve
  2. Rotary Motion control valve

Control Valve Parts and Terminology

Control Valve Parts and Working principle
Control Valve parts

Diaphragm Case

It is considered the backbone of the control valve and is the most important member of the control valve. It consists of the upper and lower sections of the control valve. It is used to support the diaphragm.

Diaphragm Plates

This plate is attached to the diaphragm to transmit the force to the equator.

Actuator Spring

It moves with the movement of the spring diaphragm. And it works on the principle of resting force.

Spring Seat

It is a plate that holds the spring in position. And it provides a smooth surface for contacting the spring adjuster.

Spring Adjuster

It usually has a wide fitting above the actuator stem or inside the yoke. Which adjusts the compression of the spring.

Yoke

This is the part that connects the body of the actuator and the control valve. Spring fits inside this yoke. Attached to the valve's travel indicator and scale yoke.

Travel Indicator

It is a pointer attached to the stem connector. This indicates travel with the valve plug.

Travel Indicator Scale

This is a graduated scale that is attached to the yoke. And it shows valve travel.

Packing Box

It is part of a bonnet assembly. According to the process, glands are inserted in it which seal the stem from all sides and do not allow the process to leak out of this path.

Bonnet

This part is mounted on the body of the control valve.

Cage

It is a cylindrical trim element. It guides the movement in a straight line with the valve seal rings in the valve body.

Valve Plug

It is a moving part that provides variable restrictions in the port.

Seat Ring

It is usually a round plate with a hole in the middle.

Actuator Stem

It is a rod that is attached between the diaphragm plate and the valve plug and connects them.

Characteristics of Control Valve

Much depends on the flow characteristics of the valve, the design of the valve, and the trim material. That is, when the actuator receives the signal, how much the control valve plug travels from its seat ring and how much flow it keeps dropping? When the valve moves through the plug actuator, the path to the flow is greater.

How many types of Control Valves?

There are two types of control valves.

  1. Linear Motion Control Valves
  2. Rotary Motion Control valves 

Generally, the following features are inherent to control flow.

Characteristics

  1. Linear Flow Characteristics
  2. Equal Percentage Flow Characteristics
  3. Quick Opening Flow Characteristics

Linear Flow Characteristics

The flow rate in the control, which has linear flow characteristics, is directly proportional to the travel of the valve plug. For example, if the valve plug travels 50%, the flow rate will be 50%. This type of control valve is most commonly used where constant gain is required.

Equal Percentage Flow Characteristics

In a control valve with this feature, when the wall plug travels uniformly, the flow rate will change very little, that is when it is close to the off position. Similarly, if the plug travels more, the flow rate will also change a lot. That is, it will be close to the full ON position. For example, if the plug travels from 20% to 30%, the flow rate will change from 4% to 6%. And if the plug travels from 80% to 90%, the floor rate will change from 47% to 70%.

Quick Opening Flow Characteristics

In the control with quick open flow features, the flow rate changes as much as the valve plug travels very little. Conversely, if the valve plug travels maximum, the flow rate changes very little. For example, if the plug travels 110%, the floor rate will change by about 40%. And if the plug travels from 80% to 90%, the flow rate changes from 77% to 95%.

Working Principle of Control Valve

Pneumatic Actuator

Pneumatic actuators require air or signal to produce a controlling process. The actuator takes the pneumatic signal force from its upper part. It then divides this signal into diaphragms. And then the diaphragm puts pressure on it. This is how the control valve gets stroked.

Devices that receive an electronic signal and run on a motor.

The control valve is a device that operates automatically. It is mostly used for pressure. The control valve operates with the help of a special part called a valve plug. This part is connected to the stem. And the stem is attached to the actuator.

Symbol of Control Valve

Control Valve Parts and Working principle
Control Valve Symbol

  • What is Control Valve
  • Parts of Control Valve
  • Types of Control Valve
  • Characteristics of Control Valve
  • Diagram of Control Valve
  • Symbols of Control Valve
  • Working Principle of Control Valve

Thanks For Reading.

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