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Valves and fittings pressure drop coefficient K (turbulent flow)

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1. Introduction
2. Pressure drop calculation

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

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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. With
ΔP_s = pressure drop through pipe singularity (valve, fitting...) (Pa)
K = friction coefficient from tables below
ρ = fluid density (kg/m3)
u_m = 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.

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

Valves and Fittings	Opening	K coefficient
90º elbow standard	-	0.75
90º elbow long radius	-	0.45
45º elbow standard	-	0.35
45º elbow long radius	-	0.2
Coupling / Union	-	0.04
Gate Valve	Open	0.17
	¾ Open	0.9
	½ Open	4.5
	¼ Open	24
Diaphragm Valve	Open	2.3
	¾ Open	2.6
	½ Open	4.3
	¼ Open	21
Globe valve – plug disk	Open	9
	¾ Open	13
	½ Open	36
	¼ Open	112
Angle Valve	Open	2 to 4
Ball Valve	Open	0
	Close 5°	0.05
	Close 10°	0.29
	Close 20°	1.56
	Close 40°	17.3
	Close 60°	206
Butterfly Valve	Open	0
	Close 5°	0.24
	Close 10°	0.52
	Close 20°	1.54
	Close 40°	10.8
	Close 60°	118
Swing check valve	-	2

Perry's Chemical Engineers Handbook, Perry, McGraw Hill, 2008, page 6-18