Friction Loss

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Friction Loss

Friction loss is the loss of energy or “head” that occurs in pipe flow due to viscous effects generated by the surface of the pipeFriction Loss is considered as a “major loss”.

Pumps require a certain amount of energy ( head ) to move water. Friction loss is calculated by the size and type of the pipe including distance in metres and vertical height on the suction side of the pump. On the discharge side we also require the size and type of pipe and the pipe diameter, the distance in metres including vertical height. We then need to know the approximate flow rate required for your application.

Example:

We want to pump water out of a dam. The pump will be located 10 metres from the dam. The vertical height from the dam to the pump is 2m.

We want to transfer water from the pump to a holding tank. The distance in metres is 290m with a vertical height of 20m. We require a flowrate at the discharge end of the pipe to be 30LPM (flowrate).

Our pipe size on both the inlet and outlet is 1 inch (25mm) rural poly or greenline.

The friction loss chart is calculated in litres per second, so 30LPM = 0.5LPS.

The pipe size of 25mm at 0.5LPS =  5.02 metres of friction loss (head) per 100 metres of pipe

We have 300metres (10m + 290m) of pipe and 22metres (2m +20m) of vertical height

5.02 x 3 = 15.06.

15.06m + 22m = 35.06m

This means we require 35.06 metres of head to pump 30 litres of water per minute.

We now look at the performance chart provided by the manufacture of the pump to see if the pump will achieve the required flowrate and head. As a guide your optimum performance would be between 1/3rd to 2/3rds range on the performance chart

We have not considered pressure in this example

Author - Paul
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