(Information supplied by Reefe Pumps and the Australian Water Pump Warehouse)
Friction is the resistance that a pipe imparts on water as it moves through it. It is a bit like putting your hand out the window of your car. When you are stopped there is no resistance, but the faster you go, the more resistance there is. It is also often compared to voltage drop in an electrical cable.
In essence the faster water moves through the pipe, the more resistance there is. The resistance is called pressure loss or pipe friction. For example, if we are moving 100L per minute through both a 2” pipe and a 3/4” pipe, the water will be moving faster in the 3/4” pipe – and hence there will be more pressure loss (friction) in the 3/4” pipe.
Additionally, it makes sense that water flows quicker through a 1m long hose than a 100m long hose. Friction works on a per meter basis. So, the smaller the pipe and the longer the pipe, the more friction (and thus less flow) will result. The following friction loss tables will give you the friction loss based on 100 metres.
Pipework Size is Critical
Pipework selection is critical to ensure good flow and to ensure that your pump is not restricted. Compare 60L/min through 20mm Poly Pipe (128.97m Head Loss per 100m) versus 32mm Poly Pipe (12.78m Head Loss per 100m). This is 10 x Less.
Velocity for Sewage and Wastewater
While size matters when pumping all liquids, when pumping raw sewage, special attention also needs to be given to the velocity. This is how fast the liquid is traveling in the pipe. The larger the pipe the less friction and hence the slower it is moving in terms of metres per second. The issue if sewage is pumped too slowly is that the solids will drop out of suspension and block the pipework over time. A rule of thumb is 1 metre/second. This value is shown on the friction loss table at any given flow rate.
Summary:
In general, larger pipes have a lower friction loss than smaller diameter pipes.
