Pressure loss System Curve  


System curve and pump curve
System Curve 1 Supplement




This section allows to enter a second pipe section for the suction side and the pressure side. Different roughness, diameters, more fittings, valves etc.




note

Pressure loss of the viscous flow

A. Piping


The equation of Darcy-Weisbach allows to determine the pressure loss of straight piping and bends. Darcy Friction Factor is calculated by the law of Hagen-Poiseulle for laminar flow. For transition zone and turbulent flow Darcy Friction Factor is calculated by the equation of Colebrook (Moody). Laminar flow through bends is calculated according to Ghia, non-laminar flow according to Krüger. Data for suction side and pressure side is collected separately to determine the pressure rise accross the pump. Absolute pressure on the pumps suction side must stay below its NPSH value to avoid cavitation caused by evaporation inside the pump. We start with choosing the roughness of the inner pipe wall. Click the link roughness for help.



Roughness    mm

Suction side

Pressure side

Straight Piping

Means of Calculation Steel Pipe Plastic pipe
dSuct,2   mm      Length    m   dPressure,2   mm      Length    m

Bends 90º


Means of Calculation Steel Pipe Plastic pipe
Number        d =dSuct,2      r/dSuct,2  Number       d =dPressure,2      r/dPressure,2 



B. Miscellaneous: fittings, filter, valves, flow meter, heat exchanger, etc.


Suction side

Pressure side

Flow coefficient cv of a component equals its water flow in [gal/min] at a pressure loss of 1 [psi]. Flow coefficient kv equals its water flow in [m³/h] at a pressure loss of 1 [bar]. The tab above the entry area leads to kv values of various valves. Flow coefficients cv can be converted to kv - see link kv or choose the calculator from the main menue. More theory as always on the left corner of the entry area.



Flow coefficient    kv   cv kv for diverse fittings
  Name    Number    Name    Number 
  kv  m³/h H20 @ Δp = 1 [bar]   kv  m³/h H20 @ Δp = 1 [bar]
  Name    Number    Name    Number 
  kv  m³/h H20 @ Δp = 1 [bar]   kv  m³/h H20 @ Δp = 1 [bar]
  Name    Number    Name    Number 
  kv  m³/h H20 @ Δp = 1 [bar]   kv  m³/h H20 @ Δp = 1 [bar]

Suction side

Pressure side

Friction Factor K is the proportional factor of the Darcy-Weisbach equation. Click the tab above the entry area for K values of various valves. More theory as always on the left corner of the entry area.



Resistance coefficient   K K for diverse fittings
  Name    Number    Name    Number 
  Resistance coefficient K  [-]   Resistance coefficient K  [-]
  Diameter   mm   Diameter   mm
  Name    Number    Name    Number 
  Resistance coefficient K  [-]   Resistance coefficient K  [-]
  Diameter   mm   Diameter   mm
  Name    Number    Name    Number 
  Resistance coefficient K  [-]   Resistance coefficient K  [-]
  Diameter   mm   Diameter   mm

Suction side

Pressure side

Sometimes neither a cv value nor a friction factor is known for the component in question. But pressure loss and flow for one point of operation. This data can be used as reference the same way we use cv values. Darcy-Weisbach equation allows the conversion to different flows, pressure losss and densities.



one operating point given
  Name    Number    Name    Number 
  Pressure loss   bar   Pressure loss   bar
  Volume flow   m³/h   Volume flow   m³/h
  Density   kg/m³   Density   kg/m³
  Name    Number    Name    Number 
  Pressure loss   bar   Pressure loss   bar
  Volume flow   m³/h   Volume flow   m³/h
  Density   kg/m³   Density   kg/m³





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