Control Valves Steam

Overview

Engineering reference data for Control Valves Steam in fluid mechanics.

Key Formulas

Reynolds Number

$Re = \frac{\rho v D}{\mu}$

Ratio of inertial to viscous forces — determines flow regime.

Bernoulli's Equation

$P + \frac{1}{2}\rho v^2 + \rho g h = \text{const}$

Conservation of energy for steady, inviscid, incompressible flow.

Continuity Equation

$A_1 v_1 = A_2 v_2$

Conservation of mass for incompressible flow.

Darcy-Weisbach

$\Delta P = f \frac{L}{D} \frac{\rho v^2}{2}$

Pressure drop due to friction in a pipe.

Variables

Steam Control Valve Design Procedure

The proper sizing of steam control valves follows a two-step processType:

1. Determine the Pressure Coefficient (Pcoef) from the absolute inlet pressure and allowable pressure drop
2. Select the Flow Factor (Kv) using Pcoef and the required steam flow rate

Pressure Coefficient Formula

$P_{coef} = \frac{\Delta P}{v}$

Where:

• $P_{coef}$ = pressure coefficient
• $\Delta P$ = pressure drop across the valve (bar)
• $v$ = specific volume of steam at inlet conditions (m³/kg)

Critical Pressure Drop Limitation

Important: The pressure drop across a control valve cannot exceed the critical pressure drop, which is approximately 42% of the absolute inlet pressure. Attempting to exceed this limit will result in choked flow and loss of control capability.

Pressure Coefficient Reference Table

Flow Factor Reference Table

Interactive Charts

References

• Original Source