Control Valve Sizing Excel tool Without Iteration: Liquid Application

This user-friendly Excel tool is designed for quick and precise control valve sizing for liquid applications. It eliminates the need for iterative methods while maintaining accuracy in accordance with ISA/IEC liquid control valve sizing standards. Users can input key parameters such as upstream and downstream pressures, flow rate, liquid density, and pipe diameter to calculate the flow coefficient (Cv) and select an appropriately sized valve. The tool simplifies valve selection, optimizing it for various process conditions

Step-by-Step Procedure for Valve Sizing

Step 1:Input Data Preparation

 You will need the following data based on your specific application:

• Upstream Pressure (P1): The pressure before the valve.
• Downstream Pressure (P2): The pressure after the valve.
• Flow Rate (Q): The desired flow rate through the valve.
• Liquid Density: The density of the fluid (you can look this up if it’s not already known).
• Pipe Diameter (D): The internal diameter of the pipe leading to and from the valve.
• Pressure Drop (ΔP): The difference between upstream and downstream pressures (ΔP = P1 – P2).

Step 2:Inputting Data in to the Excel Tool

 Once you have these above values:

• Open the spreadsheet and input your values into the respective fields for P1, P2, Q, Liquid Density, and Pipe Diameter.
• Ensure the pressure units (e.g., psi, bar) and flow units (e.g., m³/h, GPM) match your data. If needed, you can use conversion factors to adjust these units.

Step 3:Understanding the Output of Control Valve Sizing Calculation

 The spreadsheet will calculate and provide you with:

• Flow Coefficient (Cv): This value tells you how much flow the valve allows under a specific pressure differential.
• Valve Sizing: Based on the Cv value, the sheet should suggest a valve size that can handle the calculated flow.

Step 4:Adjusting Variables

You can modify the flow rate, pressure drop, or any other inputs to see how it affects the valve sizing. This allows you to optimize the selection of the valve for different scenarios or operating conditions.

Troubleshooting the Errors in the Control Valve Sizing

If you are not getting the results you expect, here are some checks:

• Make sure the units are consistent (pressure, flow rate, etc.).
• Ensure that the pressure drop (ΔP) is within a reasonable range for control valve operation. Too high or too low a pressure drop could lead to cavitation or other issues.

Use of this ControlValve Sizing Excel Tool

If you want to proceed with specific tasks like:

• Sizing calculations: You can use your known inputs (flow rate, pressure, etc.) and get the corresponding valve size or Cv.
• Scenario analysis: You can adjust inputs to see how valve size or Cv changes under different process conditions.

ControlValve Sizing Excel Tool – Download link

Refer the below link to download the Excel Tool for Control Valve Sizing Excel tool Without Iteration: Liquid Application

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Note: This Excel worksheet, as featured in the July 2022 issue of Control Magazine, is designed for simplified liquid control valve sizing. It fits on a single page and generates liquid Cv calculations that match precisely with those produced by the iterative method used in the ISA/IEC control valve sizing standards. Additionally, the second tab of the worksheet includes a copy of the Control Magazine article that explains the methodology in detail. Special thanks to Control Magazine for providing the detailed insights and guidance on this important topic.

FAQ on Control Valve Sizing

How to calculate control valve sizing?

Control valve sizing involves determining the correct valve size that can handle the required flow rate at the desired pressure drop. The general process involves:

Step 1: Collect process data, including flow rate, pressure drop, fluid type, and temperature.

Step 2: Use the Cv equation (flow coefficient) for liquids: 

• Q is the flow rate (gpm or m³/h)
• ΔP is the pressure drop across the valve (psi or bar)
• SG is the specific gravity of the fluid
• Cv is the valve’s flow coefficient (which you’ll be calculating).

Step 3: Using the process conditions, calculate the required Cv, and select a valve that has a Cv close to the calculated value.

For compressible gases, more complex formulas involving pressure ratios and compressibility factors may be used.

Click here for Control Valve Flow Coefficient (Cv) in Industrial Applications

What software is used for control valve sizing?

Several specialized software tools are available for control valve sizing, including:

• Fisher Specification Manager (by Emerson)
• ValvSize (by Samson)
• FlowServe Performance!Nxt
• Crane’s Flow of Fluids Software (for detailed calculations of pressure drop and flow in piping systems)
• Siemens SIZER (for industrial applications)

These tools help automate the valve sizing process and ensure correct selection based on various process parameters.

Click here for Control Valve Leakage Testing, Types, and Calculation Standards

What is FL in control valve sizing?

FL is the liquid pressure recovery factor of a valve, which measures how much the pressure of the liquid recovers downstream after passing through the valve. It represents the valve’s tendency to experience cavitation—a destructive phenomenon where vapor bubbles form and collapse inside the valve.

A lower FL value means a higher potential for cavitation. This factor is used in valve sizing equations to predict if cavitation will occur under the process conditions.

How do you determine the size of a valve?

To determine the size of a valve:

• Step 1: Use the valve sizing equations to calculate the required flow coefficient (Cv) based on the process conditions (flow rate, pressure drop, fluid type).
• Step 2: Compare the calculated Cv with the Cv values of available valves.
• Step 3: Select the valve size that provides the required Cv at a reasonable percentage of the valve’s opening (typically 60-80% open for optimal control).
• Step 4: Ensure the valve can handle the required pressure and flow without causing cavitation, flashing, or noise issues.

What is a good Cv value for valves?

There isn’t a universally “good” Cv value for all valves—it depends entirely on the application’s specific requirements (flow rate, pressure drop, fluid type, etc.). A well-sized valve will have a Cv that matches the process needs while keeping the valve within its optimal operating range.

Here are some guidelines:

• For fine control, you generally want the valve to operate at 60-80% open at the maximum required flow rate.
• A valve that is too large for the application (with a higher Cv than needed) will cause poor control at lower flow rates since the valve will be near-closed for most of its operation.
• A valve that is too small (with a Cv lower than needed) might cause excessive pressure drop, reduce flow, or lead to cavitation or flashing problems in liquids.

The good Cv value is the one that matches your process requirements and ensures the valve operates efficiently within its designed range.

How to calculate Cg from Cv?

Cg is the gas flow coefficient and is related to Cv. 

To convert Cv to Cg for gasses, you use the formula:

Cg=Cv×1360

This conversion helps in determining valve capacity for gas flow applications.

What is the rule of thumb for valve sizing?

A general rule of thumb for valve sizing is to select a valve that operates at about 60-80% open at the maximum flow rate. This ensures good control and allows for some flexibility in the system. Choosing a valve that’s too big can lead to poor control, while a valve that’s too small may not handle the flow properly.

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