Pump/ventilator head vs flow performance curve calculator

Calculate pump (or ventilator) head and flow for known pipeline size

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The calculator allows the analysis of fluid flow through the pipeline for the selected pump size. The analysis enables the determination of the flow through the pipeline at different pump speeds so you can calculate needed pump rpm and save energy.

Pump characteristics
Head [m H₂O]Flow [m³/hour]EditRemove
Pipe dimensions
Viscosity to input:

Pump and pipe performance curves

Based on:

@n₂=1500.0 rpm
H=84.216 m H₂O
q=89.38 m³/hour
ρ=1000.0 kg/m³

Short instructions for calculator use

What can you do with it?

Calculate the actual flow and required head of the pump (or ventilator) for known pump performance curves and known piping characteristics (diameter, length, local resistance, surface roughness)
Calculate the actual flow and head of the pump for the variable pump speed
Calculate pump flow for different pipeline lengths, different pipeline diameters, etc
Quickly and easily notice how different the thickness of the pipe wall affects the fluid flow, for the same nominal outside pipe diameter
The calculator shows visually how much of the pump's head is used to overcome the useful - static pressure and how much energy losses are due to friction in the pipeline or due to local resistance, so you can reduce the pump speed and get the same flow without energy loses.
An equation that approximates the performance curve of pump is presented
Graphic representation of the pump performance curve, pipeline and operating (intersection) points
Usable for incompressible fluid flow - liquids and gases as well, at low pressure drops
Selection of fluid from the available list
Selection of standard pipe from the available list
Applicable for round and rectangular pipelines and ducts
Selection of units of measurement in the metric and imperial system

Pump - pipeline - reservoir example

Pump characteristics


Each pump has its own unique characteristic - a curved line that shows relation of the actual head to a certain flow at constant speed. Such a curve is the characteristic of the pump. When this page loads, several values ​​of head and flow have already been entered in the pump characteristics table, and these are a characteristic of the well-known Grundfoss size 45 CP pump.

Units of measure

Before entering the pump characteristic value, you can select the units of measure for head H and flow q.

Pump performance

The calculator allows you to enter several combinations of head and flow rates in the table for the selected characteristic. At least three combinations head-flow need to be entered. The maximum number is not limited, but there is no need to enter more than five head-flow combinations.

Editing and deleting

By using the edit option, you can change existing values ​​to suit your specific pump. You can also delete unnecessary operating points, but the calculator does not allow the number of entered head - flow combinations to be less than three.

Pump speed

The calculator expects you to enter the value of the pump speed (rpm) - n₁ at which the entered head - flow combinations apply. In the next text field - n₂, the calculator allows you to enter another desired pump speed (rpm). This is a very useful feature if the pump have the ability to change the speed using a frequency converter, VFD or EC motor.

Pump performance curve approximation

After entering all the quantities, an approximate function is displayed at the bottom, which shows the dependence of the pump head and flow, at variable speed n₂. That curve is visible at the pump performance diagram.

Pipe line characteristics

Pipe shape and size

The calculator allows you to use it for round pipes and rectangular channels. Before entering data for the pipeline, it is necessary to first choose one of these two types - round pipe or rectangular channel. For round pipes, you can choose one of the standard pipes offered. There are several standards available, and it is necessary to choose the nominal diameter and schedule. The calculator calculates the inner diameter and enters the value in the field - internal diameter D. If the pipe standard is not known, you can enter free values ​​for the inside diameter D, or the width W and the height H of the channel.

Other pipeline properties

For the calculation, it is necessary to enter the length of the pipeline L, the internal roughness of the pipe surface kr, as well as the static pressure - elevation E, ie. the difference in height between the inlet tank and the tank or pipe opening where the pipeline ends. The calculator expects you to enter the size of the coefficient of local resistance K - pipe bends, t pieces, reductions, valves, etc. if there are any.

Pipeline curve - characteristics

After entering these values, the calculator will be able to determine the characteristic of the pipeline - a curved line that shows the dependence of the flow through the pipeline and the pressure drop (head). That curve is visible at the pump performance diagram.

Fluid properties

The calculator requires data entry for fluid flowing through the pipeline. Density and viscosity values (kinematic or dynamic) ​​must be entered. The calculator allows you to select fluids from a list. A large number of fluids are available - both liquids and gases. It should be noted that the calculator assumes incompressible fluid flow, so it is applicable to gaseous fluids only at lower pressure drops and lower speeds.

Pump and pipe performance curves

After entering all the previous values ​​(pump, pipeline, fluid), the calculator can display curved lines that represent the characteristics of the pump and pipeline. For the calculation, it is necessary to click on the button - calculate the operating point.

Finally - Pump operating point

At the intersection of these curved lines is the operating point of the pump. The operating point of the pump is shown by the magnitude of the head H and the flow q of the pump, at the pump speed n2, for a known density and viscosity of the fluid.

Example #1

Task:pipe network calculator
For the world-famous Grundfos CR 64-5 pump, calculate required pump speed to achieve of 250 gpm.
Pump speed from the manufacturers catalogue is 1500 rpm.
The static pressure that the pump needs to overcome is 100 ft.
Pipe is ASTM A36.10 4" SCH 40 pipe, length is 2000 ft, pipe internal roughness is kr=0.01 mm, local resistance coefficient is K=10.
Flowing fluid is water.

For a known pump, we can take from the manufacturer's catalog data on the curve that shows the characteristic of the pump - the combination of head - flow.

Selecting units of measure for head and flow you can adjust calculator to enter values that you are more comfortable for you to work with with.
For this example, we need to switch to imperial units for head, flow, pipe length and elevation.
We enter this data in the pump performance table.

Then, in the part with the characteristics of the pipeline, we select pipe from the list of standard pipes, enter other data about the pipeline - length, roughness of the inner surface of the pipe and the coefficient of local resistance.
For this example, we enter the static pressure that the pump needs to overcome - elevation is 100 ft.
In the fluid panel we can select water from the list, so density and viscosity is available in the calculator.

When you click on Calculate button in the pipe curve area, you will get pump operation point at 1500 rpm. Flow rate for that speed is 394 gpm, which is much more than we need, so we can reduce the pump speed and get needed flow with much less energy used.

With multiple trial and error calculations, entering variable pump speed in the n₂ text field, we finally get desired flow rate of 250 gpm at 1095 rpm.

Task result is at the end 1095 rpm.

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