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Local pressure loss
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Local pressure loss calculation

The local pressure losses corresponding by the valves and fittings in the hydraulic networks are expressed by the following relation:

Local pressure loss, losses, fittings, calculation

  • Dps = local pressure loss in Pa
  • p = density of the fluid in kg/m3
  • V = rate of flow in m/s
  • K = coefficient depend on the nature of local resistance

Dynamic pressure, density, flow = Dynamic pressure of the fluid.

The local pressure losses are classified in 2 categories:

  • Those which are with constant value whatever the diameter of the network used, such as the changes of section (reductions, inlets and outlets of the pipes)

  • Those which vary according to the diameter of networks, whose pressure loss is due primarily by friction and turbulence occurring such as for example in a valve.
K-factor with constant value

It should be noted that the following values all are established according to the smallest diameter.

This value can be converted on the largest diameter by (dlarge/dlitle)4.

Changement de section
K
- Réduction concentrique - élargissement d1/d2 = 0.90
0.026
- Réduction concentrique - élargissement d1/d2 = 0.80
0.13
- Réduction concentrique - élargissement d1/d2 = 0.75
0.16
- Réduction concentrique - élargissement d1/d2 = 0.67
0.28
- Réduction concentrique - élargissement d1/d2 = 0.50
0.5
- Réduction concentrique rétrécissement d1/d2 = 0.90
0.008
- Réduction concentrique - rétrécissement d1/d2 = 0.80
0.041
- Réduction concentrique - rétrécissement d1/d2 = 0.75
0.049
- Réduction concentrique - rétrécissement d1/d2 = 0.67
0.085
- Réduction concentrique - rétrécissement d1/d2 = 0.50
0.16
Entrée et sortie conduite  
- Entrée conduite de niveau - r/d = 0.00 (angle vif)
0.5
- Entrée conduite de niveau - r/d = 0.02
0.28
- Entrée conduite de niveau - r/d = 0.04
0.24
- Entrée conduite de niveau - r/d = 0.06
0.15
- Entrée conduite de niveau - r/d = 0.10
0.09
- Entrée conduite de niveau - r/d > 0.15 (bien arrondie)
0.04
- Entrée conduite saillante
0.78
- Sortie canalisation
1
Divers  
Comptage (Consulter normalement le fabricant)  
- Compteur à disque (K : 3,4 à 10)
10
- Compteur rotatif
10
- Compteur à piston
15
- Compteur à turbine (K : 5 à 7.5)
7.5
Branchement radiateurs y/c robinetterie  
- Piquage sur réseaux aller et retour, radiateur, robinetterie
15
Ensemble chaudière y/c robinetterie  
- entrée et sortie chaudière y/c changements brusques de sections, entrée et sortie, vanne, tuyauterie de dérivation, piquage, du vase d'expansion (8 à 12)
12
Tronçon entre 2 piquages  
- sans variation de section
1.5
- avec variation de section
3.5

 

K-factor depend on the diameter used

This calculation must be carried out separately for each pipe size, using the appropriate velocity within that pipe section.


Evaluation of local pressure loss

The singular pressure losses are expressed by:

K-factor, local pressure loss

Conversely, it is possible to know the value of K according to the pressure loss (read on an abacus)

Pressure loss, flow rate, fluid

  • V = Rate of flow in m/s
  • DPs = Pressure loss in Pa
  • p = Density of the fluid in kg/m3 (depends on the temperature)
  • K = coefficient depend on the nature of local resistance

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