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How do you size a hydraulic or air network with a pump or turbine?
Sizing a network means choosing the pipe diameters and the machine that will deliver the required flow at the lowest overall cost. Start from the required flow rate, set the diameters from a reasonable velocity, calculate the major and minor head losses, then plot the system curve, the head to supply against flow rate: H = Hstatic + k Q². The pump or fan is chosen so that its operating point, where the two curves cross, falls close to its best efficiency; a turbine makes use of the available head less the losses. Example: lifting 20 m³/h by 12 m with 6 m of head loss at that flow requires 18 m of pump head; at 25 m³/h the losses rise to 9.4 m and the head to 21.4 m.
Sizing formulas
- Hsystem: head to supply to the fluid, in m, at flow rate Q
- Hstatic: elevation difference between suction and delivery, in m; ΔPtanks: pressure difference between the tanks, in Pa
- k Q²: network head losses, proportional to the square of the flow rate in turbulent flow
- Poutput: power transferred to the fluid, in W; Hnet: head available to a turbine, in m
System curve: example
| Flow rate (m³/h) | Head loss (m) | Head to supply (m) |
|---|---|---|
| 0 | 0 | 12 |
| 10 | 1.5 | 13.5 |
| 15 | 3.4 | 15.4 |
| 20 | 6.0 | 18.0 |
| 25 | 9.4 | 21.4 |
Detailed explanations and calculation in Mecaflux
Sizing fluids networks is mainly in calculating the head loss, and pumps that suits the best to provide the desired flow rate.
The aeraulic and hydraulic systems are sensitive to size, power consumption, operating, maintenance and installation costs are determined by the pump turbine or fan to install, but also by the conduits. Pipe sizes, depending on the imposed flow, determine the pressure drop, and therefore the power consumption of the pump / fan or energy output of the hydraulic turbine.
When the network is complex, and that the fluid can take several paths, it will opt for the easy way (with minimum pressure drop). To make sure you can control the flow after a stream separation, you must place the valves, whose aperture setting will adjust the flow rate in each branch. A phase adjustment network, is expected after installation of valves.
Mecaflux standard is sufficient to study a simple network, But for detailed, frequent, or networks of branched fluid studies, we save time by using Mecaflux Pro3D: fluid networks design with Mecaflux Pro3D
With Mecaflux standard, the parameters of a pumping system or turbine are designed simply with pumps and turbines tab. The flow parameters, head loss, cavitation, output power, power consumption, efficiency, hydrostatic head ... are updated every time you change the data.
It is in this tab you enter the major and minor losses, calculated in your pumping system or turbine to assess the power of your pump, check if it does not cavitate or evaluate the power a turbine will produce....
Frequently asked questions
What velocities should be targeted in pipes?
As a rule of thumb: 0.5 to 1.5 m/s at the suction of a water pump, 1 to 2.5 m/s at the delivery, 3 to 8 m/s in ventilation ducts. Faster, head loss and noise increase; slower, the pipes cost more.
Why install balancing valves?
In a branched network, the fluid takes the least resistant branches first. Valves adjusted after commissioning distribute the required flow to each branch.
What changes with a turbine?
The logic is reversed: the available gross head, less the head losses of the penstock, gives the net head, and the recovered power is η × ρ g Q Hnet.
Which software should I use to size my network?
Mecaflux Standard is enough for a simple network, with its pumps and turbines tab that recalculates flow, head loss, cavitation and power. For branched or looped networks, Mecaflux Pro3D models the whole network in 3D. Mecaflux also offers a study of your project or training on the software.