Print this page Control Valve Basics – Sizing & Selection
A. Bhatia, B.E.
Course Outline
Control valves are imperative elements in any system where fluid flow must be monitored and manipulated. Selection of the proper valve involves a thorough knowledge of the process for which it will be used. When implementing a valve into a process, one must consider not only the appropriate type of valve and its material of construction, but also the correct sizing to ensure it performs its designated task.
This 4-hour course provides an overview of control valve with emphasis on the sizing and selection.
This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.
Learning Objective
At the conclusion of this course, the reader will:
- Differentiate between various types of valves and the benefits of each;
- Understand the operation of control valve in a control loop;
- Understand how to evaluate and apply actuators and positioners for specific applications;
- Understand the basic hydraulics and the relationship between the Cv, flow rate and pressure drop;
- Understand how to size valves for any flow condition likely to be found in a process plant;
- Understand how to select the proper valve characteristic for a given process;
- Understand how the installed characteristics can match closely to the inherent characteristics;
- Understand the methods to address system performance issues such as cavitation, flashing and chocked conditions;
- Learn the parameters such as material selection, pressure-temperature rating, safe action and tight shut off on the selection of valve;
- Learn the terms such as rangeablity, valve authority and turndown ratio of valve;
- Understand if the control valves can be installed in parallel or in series: and
- Learn the various issues affecting control valve performance – deadband, stiction, valve gain etc.
Intended Audience
This course is for mechanical, instrumentation and process engineers & technicians involved in sizing, selecting and applying process control valves. No specific prerequisite training or experience is required.
Benefit to Attendees
The course will be extremely helpful to the readers who desire to build on their knowledge on the process systems and the skilled professionals who have learnt the trade informally on the job.
Course Introduction
A control valve is used to permit or restrain the flow of fluid and/or adjust the pressure in a system. A complete control valve is made of the valve itself, an actuator, and, if necessary, a valve control device. The actuator is what provides the required force to cause the closing part of the valve to move and the valve control devices keep the valves in the proper operating conditions; they can ensure appropriate position, interpret signals, and manipulate responses.
When implementing a valve into a process, one must consider the possible adverse occurrences in the system. This can include noise due to the movement of the valve, which can ultimately produce shock waves and damage the construction of the system. Cavitation and flashing, which involve the rapid expansion and collapse of vapor bubbles inside the pipe, can also damage the system and may corrode the valve material and reduce the fluid flow.
This course provides understanding of the basic principles, applications and practices for the selection of appropriate control valves.
Course Content
This course content is in the following PDF document:
Control Valve Basics – Sizing & Selection
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Course Summary
A control valve is the final control element in a process control. Thus the effectiveness of any control scheme depends heavily on the performance of the control valve. The proper design and fabrication of the valve is very important in order to achieve the desired performance level. Moreover control valves are of different size and shapes. There are distinct guidelines for selecting the valve size and shape depending on load change, pipeline diameter etc. To properly select a control valve, the following fluid and system properties must be known:
- Medium - What is passing through the valve? – If it is a special liquid give specific gravity (at flowing temperate), critical pressure, vapour pressure and viscosity.
- Pressures - What is the maximum pressure that the valve needs to be rated for?
- What are the upstream and downstream pressures for each of the maximum, normal and minimum flow rates?
- Flow rates - Maximum, normal and minimum. The maximum is used to select the valve size, the minimum to check the turndown requirement and the normal to see where the valve will control.
- Temperature - Maximum temperature for design plus temperatures at maximum, normal and minimum flow conditions.
Quiz
Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.
DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.
