1. What is Cv in Flow Rate?

Definition: The valve flow coefficient (Cv) measures a valve's capacity to flow fluids. It's defined as the flow rate in gallons per minute (GPM) of water at 60°F that will pass through a valve with a pressure drop of 1 psi.

Purpose: Cv helps engineers select properly sized valves for specific flow conditions and compare flow capacities of different valves.

2. How Does the Cv Calculator Work?

The calculator uses the formula:

Where:

• \( C_v \) — Valve flow coefficient (dimensionless)
• \( Q \) — Flow rate (GPM)
• \( \Delta P \) — Pressure drop across valve (psi)
• \( SG \) — Specific gravity of fluid (dimensionless)

Explanation: The formula calculates how much flow a valve can pass at a given pressure drop, adjusted for fluid density.

3. Importance of Cv Calculation

Details: Proper Cv calculation ensures valve sizing matches system requirements, preventing flow restriction or excessive pressure drop.

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

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

Q2: How does Cv relate to valve size?
A: Generally, larger valves have higher Cv values, but design (ball, gate, globe, etc.) also significantly affects Cv.

Q3: When would I need to calculate Cv?
A: When selecting valves for new systems, troubleshooting flow issues, or comparing valve performance.

Q4: What's the difference between Cv and Kv?
A: Kv is the metric equivalent (m³/h at 1 bar drop). Kv = 0.865 × Cv.

Q5: Does Cv change with fluid viscosity?
A: The standard Cv formula assumes turbulent flow. For viscous fluids, correction factors may be needed.