1. Definition
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 preproject, 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...)
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.
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
Source
Mecanique et Rheologie des
Fluides en Genie Chimique, Midoux, Tec et Docs, 1993,
pages 329331
Perry's Chemical Engineers
Handbook, Perry, McGraw Hill, 2008, page 618
