Valves and fittings pressure drop coefficient K
Equivalent length key pipe components
Singularity coefficient key pipe components
Partially filled pipe
Control valve sizing for gases
Pressure safety valves
Velocity in pipes
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.
Equation 1 : pressure drop through a pipe singularity (valve, fitting...)
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.
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.
2. 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
Note : Re>4000 : turbulent regime
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