Control Valve Performer

Introduction to Control Valve Performer app

What is control valve performance curve?

Every process plant consists of four main components, 1) devices which generates the flow 2) devices which carry the fluid from one location to other, 3) devices which control the quantity of fluid flow and 4) devices which combines different fluids and generates the required product. The most common control element in the process control industries is the control valve. The control valve manipulates a flowing fluid to compensate for the load disturbance and keep the regulated process variable as close as possible to the desired set point. Control valves are playing a vital role in modern manufacturing process industries around the world to generate quality products.

The flow rate through a valve is controlled by manipulating the amount of open passage available for fluid flow. The amount of available fluid passage varies from 0 % (fully closed) to 100 % (fully open). The flow passage variations are achieved by a set of fixed and moving elements (also referred as valve trim) in control valve.

The relationship between valve stem (moving parts) position and the flow rate through a control valve is described by a curve called the valve's flow characteristic curve, or simply the valve characteristic. Typically, these characteristics are plotted on a curve where the horizontal axis is labeled in percent travel and the vertical axis is labeled as percent flow.

Control valve trim design and performance curve

The synergy between what is demanded and what is supplied by the valve can be achieved by re-shaping the valve trim to get desired valve characteristics. The operating parts of a valve which are normally exposed to the process fluid are referred to as 'valve trim'. Usually parts like stem, plug, disc, seating surface etc. are called as valve trim. Valve trim is the physical shape of the plug and seat arrangement. The shape of the valve plug determines the flow characteristics of the valve.

Different valve characterizations may be achieved by re-shaping the valve trim. For instance, the plug profiles of a stem-guided globe valve may be modified to achieve the common quick-opening, linear, and equal-percentage characteristics. The inherent characteristic curve is a plot of the percent of valve opening vs. the percent of maximum flow coefficient (CV). This is determined by measuring the flow rate at various positions of valve travel with a fixed differential pressure across the valve. The CV value is calculated at each valve position using a form of the generalized Control Valve CV equation.

Quick Open : A quick opening valve plug produces a large increase in flow for a small initial change in stem travel. Near maximum flow is reached at a relatively low percentage of maximum stem lift. Quick open plugs are used for on-off applications designed to produce maximum flow quickly.

Linear : The equal percentage valve plug produces the same percentage change in flow per fixed increment of valve stroke at any location on its characteristic curve. The equal percentage is the characteristic most commonly used in process control.

Equal Percentage : An inherently linear characteristic produces equal changes in flow per unit of valve stroke regardless of plug position. Linear plugs are used on those systems where the valve pressure drop is a major portion of the total system pressure drop.

Need for different trim design and characteristic curves

A control valve is a part of the complete fluid flow system. The fluid flow system may include other components like a pump, heat exchanger, reactor, piping etc. Considering all other components in the system, it is necessary to achieve desired flow characteristic curve. This is referred as installed valve characteristics.

Imagine that the process needs a linear increase in the flow rate. As pressure drop is the function of flow rate, the system pressure drop might be linear or non-linear depending on various components in the complete flow system. In case if system pressure drop is also linear, a linear characteristic curve will satisfy the purpose. But in case if the system pressure drop is non-linear, we may need to go for quick opening or equal percentage control valve.

Hence, control valve trim is designed and manufactured in a variety of different characteristics to provide the desired installed behavior.

Computational Fluid Dynamics and performance curve

In order to select an appropriate control valve for process control, it is necessary to estimate the characteristic curve of each valve. The control valve design starts with a required maximum value of valve coefficient and its variation with the percentage of opening. Every valve design goes through design variation to satisfy required performance curve. Performance curve can be evaluated by measuring a flow rate vs. valve opening in a physical test setup. Doing such studies for each design variation is very time consuming and costly. Computational Fluid Dynamics is an effective alternative to evaluate performance curve during design stage for the control valve.

Computational Fluid Dynamics or simply CFD is an art/method/science/technique of solving mathematical equations governing different physics including a flow of fluid, a flow of heat, chemical reactions, phase change and many other phenomena. When applied to control valve performance curves estimation, it's about the solution of water flow equations in a control valve at various opening conditions. It helps valve designers to quickly calculate the valve coefficient, understand flow behavior inside the valve and to optimize the design for required valve characteristics.

Traditionally, CFD is considered as three step processes, viz. pre-processing, solving and post-processing the results. In case of control valve performance curve evaluation, pre-processing involves creating 3D CAD model of a control valve, preparing CAD model for CFD meshing, creating a mesh inside a valve, creating solution setup and solution of flow equations. After the solution of flow equations, flow rate across inlet and outlet of a valve is calculated to get valve coefficient. This process is then repeated for different opening position to get a performance curve.

Few of the major obstacles for using CFD in control valve performance calculation includes the complexity of valve geometry, compute power and time required for multiple opening conditions.

What is Control Valve Performer app?

In a traditional way, calculating control valve performance curve using CFD involves the following process.

  1. For each opening position, creating 3D CAD model of control valve, extracting fluid domain and creating a CFD mesh.
  2. Doing required CFD setup and conducting analysis for number of opening conditions (typically between 5 to 10 depending on the accuracy of performance curve required).
  3. Combining a valve coefficient value and generating a performance curve

The process needs CFD expertise, its compute-intensive and typically takes days to complete.

Control Valve Performer (CVP) is a cloud-based Software-as-a-Service (SaaS) from simulationHub, that uses CFD (Computational Fluid Dynamics) as a tool to simulate and plot the flow characteristic curve of a control valve. CVP is developed specially for design engineers and manufacturers to help them simulate the performance of their design, without having any knowledge of CFD. The app only needs a control valve geometry, number of opening conditions and flow direction. All CFD setup, calculation, and result extracted is automated using specifically written algorithms for control valve performance evaluation.

All CFD computations are done using cloud computing. The app does not need any high-end local machine and even can be used from mobile / tablet devices. Once the setup is submitted from computation, ready-to-use valve performance PDF report is generated within minutes. The report includes all setup information, a valve characteristic curve, and more detailed CFD results. CVP application supports performance evaluation of rotary, lift and on/off type valves.

User interface

Following are the major components of Control Valve Performance app interface:

Simulation details and help toggle button : Access the simulation details, help and support menu. This allows opening the simulation details page. A quick link to help items like getting started guide, video library and forum is given. You can also raise the support ticket for opened simulation.
Simulation stage navigation toggle button : This button toggles the stage navigation menu of left.
Navigation menu for an individual stage : A typical simulation includes a number of main stages. Each main stage includes a number of sub-stages. For example, the location and wind condition stage has two sub-stages, location & wind rose and wind conditions for simulation. Navigation menu for an individual stage is available in the left navigation panel. Individual stage menus will change depending on the stage you have opened. For example, in result stage, you can view comfort plot, flow lines, surface pressure, contour plots etc. Clicking on each sub-stage will open the respective sub stage options. This menu follows stage dependency and color coding.
Previous & next stage access : A quick access link is given to go to previous or next simulation stage. The access to the next stage is deactivated until the current stage is completed. This menu follows stage dependency.
Stage quick access : Stage quick access is available at bottom of stage navigation panel. This quick access helps to navigate between main simulation stages. This menu follows stage dependency and color coding.
View cube : Use the View cube to orbit your design or view the design from standard view positions. If you hover on the view cube, you can see a drop-down icon at a bottom right corner with more view options.
Model view controls and settings : The model view controls contain commands used to zoom, pan, and orbit your design. The display settings control the appearance of the interface and how a model is displayed in the graphics window. You can also take the snapshot of what is displayed in the graphics window.
Model click menu : Left-click to select the object in the graphics window. Right-click to access the model menu. The model menu contains commands like to isolate, hide selected, show all objects. Left click anywhere in the graphics window to hide the model menu.
Results quick access menu : Results quick access menu is available when you open the result stage of simulation. This quick access menu helps to navigate to different results without using left navigation panel. Quick access menu contains commands to go to results like comfort plot, flow lines, contour plots etc.
Profile and help : In profile, you can control your profile and account settings, or use the help menu to continue your learning or get help in troubleshooting. This menu also contains a quick link to the dashboard. Use full-screen icon if you wish to use the app in full-screen mode.

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Mobile device modifications

View cube 6 and result quick access 9 menus are not available on mobile and tablet. A profile and help menu 10 is modified for mobile and tablet devices. You will see raise ticket and sign out buttons in the profile and help menu. Model view control and settings 7 menus are also modified and available with fewer options.

Create simulation

Start new �Control Valve Performer� from drop-down menu by creating a new simulation.

Create new simulation : Click "Create New Simulation" button on the dashboard. This will open create new simulation popup. (NOTE: The button will be deactivated in case if you do not have valid app subscription.)
Simulation details : Provide simulation name and description in given fields. If you have only one app subscription, the app will automatically be selected in template drop-down. In case of multiple app subscriptions, select the app template.
Create simulation : Click "Create Simulation" button. This will create a new simulation with provided details and open the 3D viewer for further setup.

Prepare Control Valve Model

This is the first step towards running a CFD simulation in Pedestrian Comfort Analysis app. Once a new simulation is created, you will be directed to geometry stage.

Follow below steps to get you geometry in a simulation project.

Input CAD model : Click "Input CAD Model" in valve geometry and settings stage. This will direct you to sub-stage menu for input CAD model.
Browse : If you have geometry available in your local computer, click "Browse" button. This will open "Upload Local Geometry" dialog. (NOTE: If you have geometry available on cloud storage, provide the link to geometry file and click upload. Currently, only Amazon S3 cloud storage links are supported).
Choose a file : Click on "Choose a file to upload" button to open a file browser. Select the file and click "Open" in a file browser. The selected file name will appear below the button.
Upload : Click "Upload" button to upload the file to your simulation. The time required to upload the file will depend on the size of a file. Once the file is uploaded, the 3D viewer will show the geometry and will move to the next simulation stage. You can notice that the geometry stage is marked completed (blue color) in stage quick access menu available at bottom of stage navigation panel.

Create Setup

To get the performance curve for rotating or lift control valve, you need to define valve opening conditions. Opening settings define moving parts of valve trim, an axis along which parts will move and the number of opening conditions.

Moving Part Settings : Click "Moving Part Settings" in main Valve Geometry and Settings stage. This will direct you to sub-stage menu for selecting moving parts of a control valve.
Start selection : In this stage, user have to select moving parts from whole geometry by clicking on start selection button
Add body to moving bodies : Move cursor on to the object user want to set as moving, Then right click and select "Add body to moving bodies" from options.
List of Selected bodies : This box will show list of selected objects and user can hide or delete selected objects from options given.

Selection of Axis

Select Axis : Click "Axis of Rotation" from stage Moving Parts Settings, This will open sub-stage menu in Axis selection for moving parts.
Start selection : In this stage, user have to select moving parts from whole geometry by clicking on start selection button
Select a method : There are two methods given for selecting an axis for control valve user should select one from the drop-down menu.

a. Axis using cylinder: Select method from the drop-down menu �Axis using cylinder�, then click on a button �Select cylindrical surface� after clicking this button user have to select a cylindrical surface from viewer, an axis of that cylinder should coincide which axis of moving parts.

Valve Opening Conditions:

A complete performance curve for a control valve contains valve coefficients from fully closed to a fully open condition. The accuracy of performance curve depends on the number of opening conditions considered for performance evaluation. Typically, 5 to 10 number of opening conditions are considered good for accurate representation of valve performance curve. Control Valve Performance app provides the number of conditions anywhere between 2 to 8. To avoid simulation failure, it is recommended to provide opening conditions anywhere between 20 % to 100% opening of a valve.

In case of rotation motion type, provide minimum and maximum opening angle. Minimum angle should be more than or equal to 20° and maximum angle should be less than or equal to 90°.

In case of lift motion type, provide start position and end position of valve opening condition. As the total lift travel of valve is not known, you should take care to provide the start position such that the minimum opening is more than or equal to 20 % of the total opening. It is also necessary to provide end position such that the maximum opening is less than or equal to 100%.

Once minimum and maximum rotation/lift conditions are provided, enter the total number of opening conditions. The opening conditions will be equally divided between the minimum and maximum opening value. For example, if the minimum angle is 20°, maximum angle is 90° and the number of conditions is 8, the opening angle for simulation will be 20°, 30°, 40°, 50°, 60°, 70°, 80°, and 90°. Selection procedure for valve opening condition is given below.

Valve Opening Conditions : Click "Valve Opening Conditions" from stage Moving Parts Settings. This will open sub-stage menu in Axis selection for moving parts.
Start angle and end angle : User need to give minimum valve opening condition here (for Rotating valve it should be in degrees of angular rotation and for Lift valve should be in millimeter of displacement.)
Preview and Apply settings : You can preview the valve opening conditions to confirm the opening settings. Make sure that the valve rotates or lifts in the correct direction. If the rotation or lift is in opposite direction, you can use "Reverse" button in-front of Rotation / Lift Axis to reverse the opening direction.
Save opening settings : Click "Apply" button to save opening conditions. These conditions will then be saved with valve performance study.

Fluid Volume Extraction

Fluid volume extraction is a major step in simulation, Which decides the actual flow domain inside control valve geometry to be simulated. Click �Extract Fluid Volume� from stage Fluid Volume, This will open a sub-stage menu in Fluid Volume extraction stage.

Fluid Point selection : Click on "Select Input Points" and then select on the surface of geometry uploaded at two locations so that midpoint of the segment, which is connecting these points should fall inside flow domain from where the fluid is actually going to flow.
Extract Fluid Volume : Click on Extract fluid volume button to automatically extract volume of flow domain for all the valve opening conditions.

Define Connections

To do CFD simulation at each opening position, flow direction needs to be specified. Valve connection settings allow you to specify the inlet and outlet side of the connecting pipe which helps in defining the flow direction.

Following is procedure define inlet and outlet connections:

Connection Settings : Click �Define Valve Connections� from stage Valve Connections, This will open sub-stage menu in Valve connections.
Select Inlet and Outlet : Click on Select Inlet button and then select Inlet and outlet surfaces from an extracted fluid volume. Colour codes are given to identify connections as following. Indicates Inlet Connection Indicates Outlet Connection
Save Connection settings : Click "Apply" button to save valve connection settings. These conditions will then be saved with the direction of flow with valve performance study.

Run Simulation

Control Valve Performer app uses cloud computing for all calculations. A control valve performance study needs multiple simulations depending on valve and motion type selected. To submit the simulation run and check status, do following:

Run simulation : Click "Simulation Run and status". This will open submit simulation dialogue.
Submit Simulation : To submit a job click on "SUBMIT" to submit the simulation on a cloud simulation facility. Once the submit button is clicked, the Control Valve Performer app generates geometry configuration at different opening conditions, creates the required setup and uploads the data on cloud computing facility. It is necessary not to do any modification in the design during this process.

A popup message will be shown about not modifying design during the process and credits required to run a simulation. If everything is fine then click on �Run Simulation" 3 to start the simulation submission process.

Check Status : In Simulation Status panel, The status of a job submitted will be shown in "Simulation Status" dialogue. The time required for simulation depends on the size of geometry and number of opening conditions submitted. Summary of the number of jobs submitted, the number of jobs completed, and overall job status is shown in the top section. Simulation of each opening conditions has different stages. Live feed of each stage statues will be shown for all opening conditions 5. Once the simulation is completed, progress bar for each opening condition will be marked with blue color and overall status will be marked "COMPLETED". A job completion email will be sent with a control valve performance PDF report.

For any reason, if you wish to terminate simulation, you can use "TERMINATE" 7 button. It will show a job termination popup.

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You have periodic design requirements or you work in an organization with heavy design load, we have subscription plans to suit all requirements. Take low-budget month-on-month subscription or high-credit yearly subscription.



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