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How friction affects water flow performance

How friction affects water flow performance

In most circumstances, a water pump will be required if you want to move rainwater from where it is stored to where it is needed.  Your water pump must deliver water at a flow rate and pressure that meets your needs.  
This article explores water flow and pressure losses caused by friction which significantly impacts the performance of a water flow through pipes, fittings, valves, and other obstructions. 
Friction can be caused by several factors: 
Pipe Diameter
Friction decreases as pipe diameter increases. Larger diameter pipes offer less resistance to flow, allowing water to move more freely with minimal friction. Therefore, using appropriately sized pipes can help reduce friction and maintain flow rates over longer distances. 
Pipe Material
The material and surface roughness of the pipes affect the amount of friction encountered by the flowing water. Smooth pipes, such as those made of PVC or stainless steel, experience less friction compared to rougher surfaces like galvanised steel or cast iron. Choosing pipes with smoother surfaces can help minimise friction. 
Flow Velocity
Higher flow velocities result in increased friction due to greater turbulence and shear stress against the pipe walls. While it may seem counterintuitive, reducing flow velocity can help reduce friction and improve overall pump efficiency. 
Pipe Length and Layout 
Longer pipe lengths and complex layouts with numerous bends, fittings, and valves contribute to higher friction. Each obstruction in the piping system introduces additional resistance, requiring the pump to work harder to maintain flow rates and pressure at the discharge point. 
Elevation Changes 
The elevation change between the pump and the discharge point is referred to as ‘head’. Changes in head along the pipe route also increase friction. As water moves uphill, it experiences increased resistance against gravity, while downhill sections may experience reduced friction. Properly accounting for elevation changes is essential for accurately estimating total head requirements and optimising pump performance. 
Friction affects pump performance as follows: 
Reduced Flow Rate: Friction along the piping system causes a decrease in the flow rate of water delivered by the pump. As water encounters resistance from friction while flowing through the pipes, its velocity decreases, leading to a reduction in the volume of water reaching the discharge point within a given period. 
Decreased Pressure: Friction also results in a pressure decrease along the piping system. As water loses energy due to friction against the pipe walls and obstructions, the pressure at the discharge point decreases. This reduction in pressure may affect the pump's ability to deliver water at the required pressure levels for various applications. 
Increased Energy Consumption: To overcome friction, maintain the desired flow rates, and pressure levels, the pump must work harder and consume more energy. Higher friction translates into greater energy expenditure by the pump, leading to increased operating costs over time. Minimising friction is therefore crucial for improving pump efficiency and reducing energy consumption. 
Limitations on Pump Performance: Excessive friction can impose limitations on the pump's performance. If friction exceeds the pump's capabilities to overcome them, it may fail to deliver water effectively to the desired discharge point, leading to inadequate water supply or reduced system efficiency. 


Before you purchase a water pump, obtain expert advice – particularly if your application is important and you need certainty about flow rate and water pressure. 
Rapid Plas is a family-owned business that have been making quality rainwater tanks in Tamworth for more than 30 years. Tanks are available in 24 different colours, ranging from 500L to 32,000L with a selection of shapes and styles, including round, slimline and super-slimline.    
If you need expert advice on rainwater tanks and water pumps, talk to our expert team to find out how we can help you. Call our team on 1800 816 299 or email  sales@rapidplas.com.au with your enquiry.