What is Pressure Differential Ratio Factor?
Pressure differential ratio factor xT is the ratio of pressure drop to inlet pressure at which gas flow through a valve chokes, for air.
Pressure Differential Ratio Factor Explained
Gas sizing uses x = ΔP ÷ P₁. Flow chokes when x reaches Fγ × xT; beyond that, more drop gives no more flow.
The expansion factor Y corrects for density change through the valve, falling from 1 to 2/3 at choked flow.
Pressure Differential Ratio Factor Formula
| x | ΔP ÷ P₁, limited to Fγ xT |
| γ | specific heat ratio of the gas |
Calculators for Pressure Differential Ratio Factor
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Frequently Asked Questions
What is Pressure Differential Ratio Factor?
Pressure differential ratio factor xT is the ratio of pressure drop to inlet pressure at which gas flow through a valve chokes, for air.
Where do I get xT?
From the valve maker, for the valve type, size and opening.
Why does xT matter for noise?
High pressure ratios near choking create high outlet velocity and aerodynamic noise.
Learn more on the blog
Control valve flow coefficient (Cv and Kv)
A practical guide on instrumentationblog.in with more detail on pressure differential ratio factor and how it is applied on real plants.
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