PLC

BASICS OF THE CONTROL VALVE :

Updated: Nov 15, 2020

In this article, you will learn the basic part and types of the control valve.


Control valve as the name implies used to control the flow of the fluid, control pressure, temperature and even level too by controlling the position of the valve.


There are many types of control valves are available, as per application we have to choose which valve is best suited for our application.


Control valve used to restrict the flow of the fluid based on the command of an automated signal, such as signal coming from the PLC.


There are two types of control valve available:


1. ON/OFF valve (only on/off state)

2. Throttling valve (operate in between open/close, on-state, off-state)


Main parts of the control valve :


1. Valve body

2. Valve actuator


Now in addition you can include valve positioner and valve trim (Plug) parts as a part of the control valve.


- Valve body: Valve body from which fluid flow passes through. It contains an arrangement of the valve plug and valve seat that is used to control or throttle the flow of the fluid.


- Valve Actuator: The part of the final control element which is used to provide a control valve with a required force to move the plug. Force can be pneumatic type, Hydraulic type or electrical type depends on which type of actuator you are using.


- valve Trim: Inside assembly few components used to throttle or control the flow of fluid is referred to as valve trim.


What can affect the trim of the valve :


1. Due to high temperature, pressure or higher flow rate.

2. what kind of fluid valve is controlling.

3. Based on the action of the valve.


Control valve type based on actuation :


1. Sliding stem control valve (single port, double port)



Operates in linear motion. Most such valve has a travel of fewer than 3/4 inches. Valve with this travel range come under sliding stem type valve.


This types of valve contain sliding stem types of design which pushes plug into the valve body to regulate and control the flow rate.


A stem which pushes a valve plug to regulate flow can be a disc or diaphragm.


This types of valve come up with a simple design and provide easy maintenance and troubleshooting.


Globe valve, plug valve, gate valve, pinch valve, needle valve, diaphragm valve, etc. fall under linear valve category.


2. Rotary control valve



The rotary valve operates based on the rotation of the shaft to actuate the trim. The ball valve, a butterfly valve is the example of such a valve.


Like linear valve, a rotary valve is also used to regulate the flow rate but specifically more suitable in an application where the valve is clogged by product.


Rotary valve mostly used in industries like chemical, food and beverages, pharmaceutical, sugar mill, etc. to dose and feed solid products which lead to better performance.


Rotary valve also used in gas chromatography application, too.


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