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Valves and fittings pressure drop coefficient K (turbulent flow)


1. Introduction
2. Pressure drop calculation
3. K coefficient for additional friction loss due to pipe and fittings


1. Introduction

The pressure drop through common fittings and valves found in fluid piping can be calculated thanks to a friction coefficient K. This coefficient must be determined for every fitting. In pre-project, common values are often sufficient. Usual coefficients are given in the tables below.

2. Pressure drop calculation

The pressure drop through a fitting or a valve can be calculated thanks to K.

Calculation of pressure drop through valves and fittings with K coefficient

Equation 1 : pressure drop through a pipe singularity (valve, fitting...)

With
ΔPs = pressure drop through pipe singularity (valve, fitting...) (Pa)
K = friction coefficient from tables below
ρ = fluid density (kg/m3)
um = average fluid velocity (m/s)

K coefficient in a same pipe section can be added, the pressure drop can then be expressed the following way.

Calculation of pressure drop through all valves and fittings of a pipe section with K coefficient

Equation 1 : pressure drop through all pipe singularities of a pipe section (valve, fitting...)

For compressible fluids, it is important to use the average velocity. If the pressure drop is too important and density and velocity change too much, the pipe section considered must be broken down in smaller sections to keep a good calculation accuracy.

3. K coefficient for additional friction loss due to pipe and fittings

The values below are only valid in TURBULENT FLOW

Table 1 : K coefficient for calculation of pressure drop through valves and fittings

K coefficient table for valves and fittings in turbulent flow

Note : Re>4000 : turbulent regime

Source

Mecanique et Rheologie des Fluides en Genie Chimique, Midoux, Tec et Docs, 1993, pages 329-331
Perry's Chemical Engineers Handbook, Perry, McGraw Hill, 2008, page 6-18