1. What is Valve Flow Coefficient (C_v)?

Definition: The valve flow coefficient (C_v) is a number that represents the flow capacity of a valve at fully open conditions.

Purpose: It helps engineers select the proper valve size for a given flow rate and pressure drop in fluid systems.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( C_v \) — Valve flow coefficient (dimensionless)
• \( Q \) — Flow rate (gallons per minute, GPM)
• \( \Delta P \) — Pressure drop across valve (pounds per square inch, psi)
• \( SG \) — Specific gravity of fluid (dimensionless, water = 1.0)

Explanation: The formula calculates how much flow a valve can pass with a 1 psi pressure drop when fully open.

3. Importance of C_v Calculation

Details: Proper valve sizing ensures efficient system operation, prevents excessive pressure drops, and avoids cavitation or flashing.

4. Using the Calculator

Tips: Enter the flow rate in GPM, pressure drop in psi, and fluid specific gravity (default 1.0 for water). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical C_v range for valves?
A: C_v values range from <1 for small valves to >1000 for large valves, depending on valve type and size.

Q2: Does this formula work for gases?
A: No, this is for liquids only. Gas flow calculations require additional factors.

Q3: What if my fluid has high viscosity?
A: The standard C_v formula may need correction factors for viscous fluids.

Q4: How does valve type affect C_v?
A: Different valve types (ball, globe, butterfly) have different flow characteristics even at the same C_v.

Q5: What's the relationship between C_v and valve size?
A: Generally, larger valves have higher C_v values, but the exact relationship depends on valve design.