Cv Calculator

What is Cv value?

The Cv value, or Flow Coefficient, is a measure used in fluid dynamics to describe the flow capacity of a valve or similar device. It is defined as the amount of water (in gallons per minute, GPM) that can flow through a valve with a pressure drop of 1 psi while maintaining a temperature of 60°F.

Calculating the flow rate from the Cv value involves complex computations. To simplify this, we’ve developed a Cv value and flow rate calculator for your convenience.

For detailed calculation information, please click the Formula of Calculation button below.

CvCalculate
Formula of Calculation

Liquid Flow Coefficient Cv Calculation

1. Variable Definitions

\(C_v\) Flow coefficient
\(Q\) Flow (gpm)
\(SG\) Liquid specific gravity (water=1.0)
\(P_1\) Inlet Pressure (psia)
\(P_2\) Outlet Pressure (psia)
\(\Delta P\) Pressure drop (P₁-P₂)

2. Basic Calculation Formula

\[ C_v = Q\sqrt{\frac{SG}{\Delta P}} \]
GRAT Control Valve

Note:Applicable for incompressible liquids under non-cavitation and non-blocking conditions.

Gas Flow Coefficient Cv Calculation

1. Variable Definitions

\(C_v\) Flow coefficient
\(Q_g\) Gas Flow (SCFM)
\(SG_g\) Gas specific gravity (air=1.0)
\(P_1\) Inlet pressure (psia)
\(P_2\) Outlet pressure (psia)
\(\Delta P\) Pressure drop (\(P_1-P_2\))
\(T\) Absolute Upstream Temperature (Kelvin K= °C + 273)

2. Calculation Formulas by Operating Conditions

\[ C_v = \begin{cases} \dfrac{Q_g}{125.6} \times \sqrt{\dfrac{SG_g T}{\Delta P \times P_2}} & \text{if } P_2 > \dfrac{P_1}{2} \\[2ex] \dfrac{Q_g}{62.8 \times P_1} \times \sqrt{SG_g T} & \text{if } P_2 \leq \dfrac{P_1}{2} \end{cases} \]
GRAT Control Valve

Liquid Kv Correction Calculation

1. Variable Definitions

\(K_v\) Flow coefficient
\(Q\) Liquid Flow (m³/h)
\(SG\) Liquid specific gravity
\(P_1\) Inlet pressure (psia)
\(P_2\) Outlet pressure (psia)
\(P_c\) Liquid critical pressure (bar)
\(P_v\) Vapor critical pressure (bar)
\(\Delta P\) Pressure drop (\(P_1-P_2\))
\(\Delta P_c\) Choked Pressure Drop
\(F_L\) Pressure recovery coefficient

2. Choked Pressure Drop Calculation

\[ \Delta P_c = \begin{cases} F_L^2 (P_1 - P_2) & \text{if } P_v < 0.5P_1 \\ F_L^2 \left[ P_1 - \left(0.96 - 0.28\sqrt{\dfrac{P_1}{P_c}} \right) P_v \right] & \text{if } P_v \ge 0.5P_1 \end{cases} \]
GRAT Control Valve

3. Corrected Kv Calculation

\[ K_v = \begin{cases} Q\sqrt{\dfrac{SG}{\Delta P}} & \text{if } \Delta P < \Delta P_c \text{（General flow）}\\ Q\sqrt{\dfrac{SG}{\Delta P_c}} & \text{if } \Delta P \ge \Delta P_c \text{（Choked flow）} \end{cases} \]
GRAT Control Valve

Conversion Relationship Between Cv and Kv

\[ C_v = 1.156K_v \]
GRAT Control Valve

Note: The conversion factor 1.156 is a theoretical value derived from unit conversion relationships between US gallons and cubic meters, psi and bar.

Gas Kv Correction Calculation

1. Variable Definitions

\(K_v\) Flow coefficient
\(Q_N\) Gas Flow (Nm³/h)
\(SG_N\) Gas specific weight (kg/Nm³)
\(P_1\) Inlet Pressure (bar)
\(P_2\) Outlet Pressure (bar)
\(\Delta P\) Pressure drop (\(P_1-P_2\))
\(T\) Absolute upstream temperature (Kelvin K = °C + 273)
\(F_L\) Pressure recovery coefficient

2. Calculation Formulas by Operating Conditions

\[ K_v = \begin{cases} \dfrac{Q_N}{380} \times \sqrt{\dfrac{SG_NT}{\Delta P(P_1+P_2)}} & \text{if } \dfrac{\Delta P}{P_1} < 0.5F_L^2 \text{（General flow）}\\ \dfrac{Q_N}{330} \times \dfrac{\sqrt{SG_NT}}{P_1} \times \dfrac{1}{F_L} & \text{if } \dfrac{\Delta P}{P_1} \ge 0.5F_L^2 \text{（Choked flow）} \end{cases} \]
GRAT Control Valve

Cv and Kv Conversion Relationship

\[ C_v = 1.156K_v \]
GRAT Control Valve

Note: The conversion factor 1.156 is a theoretical value derived from unit conversion relationships between US gallons and cubic meters, psi and bar.

V. Cv and Kv Conversion Relationship

\[ C_v = 1.156K_v \]
GRAT Control Valve

Note: The conversion factor 1.156 is a theoretical value derived from the unit conversion relationships between US gallons and cubic meters, and between psi and bar.

Data Sheets

Physical Constants of Various-Fluids
Critical Pressure of Common Liquids
Engineers' Help

Get Comprehensive Services for FREE!

Cv Calculator

Calculation Results

Scroll to Top