Control Valve Hydraulics for Chemical Process Engineers

Name: Control Valve Hydraulics for Chemical Process Engineers
Rating: 4.5 (2 reviews)

Know more about control valve characteristics, hydraulics, calculate its pressure drop and choose its controlling cases

Created byBoostrand Training

Last updated 1/2025

English

What you'll learn

The main functions of a control valve in a process
How a control valve works?
The valve flow coefficient
Valve inherent and installed characteristics
Calculate control valve main parameters and controlling cases

Course content

8 sections • 33 lectures • 2h 7m total length

Introduction1:40
Control valves are an essential part of any process plant. You can hardly see a process plant without a control valve as they are used to control more than 95% of process parameters.
Throughout this course, we shall see the main functions of a control valve, how they work, what is a control valve Cv or flow coefficient and how it is important in sizing and rating of a control valve.
We shall go through control valve inherent and installed characteristics and how the process configuration affects the operation of a control valve, we shall see when to use a butterfly valve as a control valve, and finally we shall go through the valve sizing procedure, how to choose the controlling case, we shall go through more than one example, carry out calculations and you shall have an excel sheet that can guide you in the future. Waiting to see you in the course and let’s start.
Before you Start0:50
What is a control valve?1:46
In order to adjust any process parameter, most probably we will need a control valve. We will have a measuring device that will send a signal to the valve to open or to close. Control valves represent the vast majority of final control elements.
By changing the control valve opening, we can control the fluid flow, so we can finally reach the required set point of the controller.
Main functions of a control valve5:54
We have many examples of using the control valve as a final control element
For example, we may need to adjust vessel level by adding control valve on the outlet line, so if the valve opening is reduced, the level starts to accumulate in a vessel, or if it opens, the level decreases, or we can adjust fluid outlet temperature from a cooler by adding a control valve on water outlet line or whatever control configuration we need.
So if the valve closes, less water will pass so the temperature on the process fluid will increase. If the valve opens, this means more water flow, which means more duty and more cooling, and so on.
So there are instruments giving the measurement of the required parameter whether it is level or temperature or pressure or whatever parameter, then it is sent to the controller, and the controller sends the signal to the valve to open or to close.

How a control valve works?1:46
This is simply through adjusting its opening, this is done by lifting the valve plug here upwards or downwards changing the area the fluid shall pass through in the valve, which is called an orifice or vena contracta.
So when the fluid passes through the vena contracta of the orifice, the flow area decreases, so this will increase the fluid velocity as per the continuity law.
On the other hand, the pressure at this point will decrease as per Bernoulli’s equation which shows how velocity or dynamic pressure is inversely proportional to static pressure.
But as the area increases again to be equal to the outlet pipe area, the fluid velocity will decrease and the pressure will increase again, but to a pressure that is less than the original pressure at the control valve inlet.
Valve cavitation3:21
Flashing3:17

Control Valve authority1:48
Control valve authority represents the fraction of control valve pressure drop to the total system pressure drop as shown in the below equation:
Actual Control Valve Pressure Drop1:36
So we have a control valve on pump discharge. We have a pump curve where the pump head decreases as the flow increases.
We have a control valve upstream piping pressure drop and downstream piping pressure drop.
Now let’s plot the pump curve.
Then let’s plot the head losses in the upstream and downstream piping on the curve.
So at a low pump flow, the pump gives us higher head, and at the same time, we have low system losses. So we shall need the control valve to exert a high pressure drop. At low system resistance, the control valve authority will approach one.
But when we need a high flow, the pump shall give us less head, and the system losses will increase. This will lead to a low valve pressure drop and the authority will drop.
Valve Installed Characteristics3:53
Inherent vs Installed Characteristics3:14

Valve sizing Procedure1:48
Calculating Control valve pressure drop3:23
Determine the controlling cases3:51
How could we determine the controlling cases? Sometimes the plant is working at full capacity, sometimes it works at a reduced capacity, there is usually also a design margin, so all plant is oversized by 10 or 20% of the normal capacity. The control valve should handle all these scenarios.
Let's have some practice0:24
Example 1: Calculate pressure drop and controlling case pump discharge valve32:46
Example 2: On tower overhead15:17
Valve sizing procedure by valve supplier1:45
Oversized vs undersized Valves5:06
Let’s Recap

Requirements

Basics of chemical engineering, if you are still a student, this course will help as well

Description

Control valves are an essential part of any process plant. You can hardly see a process plant whether in oil and gas industry or in any chemical processing plant without a control valve as they are used to control more than 95% of process parameters.

Throughout this course, we shall see the main functions of a control valve and how they work,

We shall go in deep on what is a control valve Cv or flow coefficient and how it is important in sizing and rating of a control valve.

We shall go through control valve inherent and installed characteristics and how the process configuration affects the operation of a control valve and what is the difference between inherent and installed characteristics.

Then we shall see when to use a butterfly valve as a control valve and how the valve geometry affects its characteristics.

Finally, we shall go through the valve sizing procedure, how to choose the controlling case, we shall go through more than one example, carry out calculations and you shall have an excel sheet that can guide you in the future.

These examples will teach you not only how to calculate the pressure drop of the control valve or how to choose the cases that shall affect the valve sizing, they shall even show how the whole system hydraulics interact with each other and the means to debottleneck it.

Waiting to see you in the course and let’s start.

Disclaimer:

Please note that the Excel sheets were made just for educational purposes. If you shall use it to validate a process or purchase equipment or piping, then you should validate it yourself, and using it shall be upon your sole responsibility.

Who this course is for:

Engineers who want to know more about control valves
Chemical engineering students

Control Valve Hydraulics for Chemical Process Engineers

What you'll learn

Explore related topics

Course content

Introduction4 lectures • 10min

Control Valve Operation3 lectures • 8min

Control Valve Flow Coefiicient Cv4 lectures • 15min

Control valve interaction with process system4 lectures • 11min

Effect of valve type and geometry3 lectures • 6min

Control Valve sizing8 lectures • 1hr 4min

Control Valve Details and considerations on a P&ID6 lectures • 13min

Bonus Lecture1 lecture • 1min

Requirements

Description

Who this course is for: