System curve and pump curve
System Curve 2

Define your system curve in 5 steps

1. Configure the flow diagram. Click valves open or close.
2. Enter title and medium.
3. Parameters for frictionless flow (Bernoulli).
4. Parameters for viscous flow (pipe friction / Colebrook, valves, etc.).
5. Save your data.

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p 1

p 4

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h 1

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klick valves to open

Characteristic´s name
note
Design flow*	m³/h

Fluid				Temperature		ºC
Density*		kg/m³		Dyn. Viscosity (Newton)*		mPas

Frictionless fluid flow

Bernoulli´s equation stands for all parameters that influence pressure loss in frictionless regime: absolute pressures, suction height, height of discharge and speed (diameter). Pressure loss caused by friction and turbulence we deal with further down. 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.

Suction side

Pressure side

Bernoulli

Steel Pipe

Plastic pipe

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p1	bar,abs	Absolute pressures!	p4=p1
h1*	m		h4=h1
pipe behind expansion tank		Pumps ports	pipe in front of expansion tank
d1*	mm	d2* mm d3* mm	d4=d1

Copy the following data from characteristic 1 yes no

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,1 mm Length m

dPressure,1 mm Length m

Bends 90º

Means of Calculation

Steel Pipe

Plastic pipe

Number d =dSuct,1 r/dSuct,1

Number d =dPressure,1 r/dPressure,1

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

First we look at components with a known maximum pressure loss. Filters have to be changed or cleaned at maximum pressure drop. Components that tend to plug or become incrusted have to be cleaned at maximum pressure drop. 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.

Δ p = constant

Name Pressure loss bar	Name Pressure loss bar
Name Pressure loss bar	Name Pressure loss bar
Name Pressure loss bar	Name Pressure loss bar

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 k_v c_v

k_v 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

System curve and pump curveSystem Curve 2

Frictionless fluid flow

Suction side

Pressure side

Pressure loss of the viscous flowA. Piping

Suction side

Pressure side

Straight Piping

Bends 90º

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

Suction side

Pressure side

Suction side

Pressure side

Suction side

Pressure side

System curve and pump curve
System Curve 2

Pressure loss of the viscous flow

A. Piping