How to Calculate Total Head

To know How To Calculate the Total Head Requirement, you will need to know 3 things:

1. Static Head
2. Pipe Friction Loss
3. Discharge Pressure

The total of the above 3 things will give you your ‘Total System Head Requirement’ in meters.

1. The Static Head, also known as Vertical Lift, is the height (below ground and above ground) that water has to travel as it moves through your discharge pipe.
2. Frictional Loss – As water flows through your discharge pipe, friction is created, from water rubbing against the inside of the pipe which slows down the water flow. The length of the pipe, the internal diameter of the pipe and the amount of elbows and bends in a pipe all affect the pipe friction. Dirty water such as grey water and sewage has a different pipe friction to clean water.
3. Discharge Pressure Required at the discharge outlet pipework.

Example: (This example is for a submersible bore pump)

1 – Static Head = from the ‘Pump Set Depth’ to the discharge pipework outlet at its highest point. Let’s say as an example it is 45 metres (35m below ground and 10m above ground).

2 – Frictional Loss = The easiest way is to use an online Pipe Friction Loss Calculator where you will input the flow rate, pipe diameter and length.
You can get a lot more technical by working out the internal pipe ID, variations in pipe type and every bend and elbow. However, as this is just a general guide, we will keep it simple.

3 – Discharge Pressure Required = In this example we are operating reticulation sprinklers that require 250kpa pressure or 25 metres. (You will need to confirm required system operating pressure).
PSI ÷ 1.42 = Meter Head eg: 36PSI ÷ 1.42 = 25.35m
Kpa ÷ 9.81 = Meter Head eg: 250kpa ÷ 9.81 = 25.48m

Therefore the Total Head will be:

1. Static Head =  45 metres
2. Friction Loss = 15 metres
3. Discharge Pressure = 25.0 metres

Total System Head Requirements = 85m

Note * There are other factors that need to be considered when calculating Total Head, such as Water Temperature, SG of Water, number of 45° & 90° Elbows installed, Isolation Valves, Check Valves, System Pipework such as long reticulation pipe runs. These losses also need to be factored into the calculation.

Now that you know the total head, you will also need to know the flow required to operate your system.  With the ‘total head’ and ‘flow’, you can now read the flow chart for the pump and select the correct bore pump.