Project: sc090025/R1

Figure 3.15: Example of typical generic pump system layout 
The plotting of the pump curve and system curves on the same graph will provide indication of 
the theoretical pump discharge rate where the two cross. Where the static head can var,y it will 
be necessary to plot system curves for high and low levels to check the pump meets all 
operating criteria. 
Incorporating the pump efficiency curve will indicate the efficiency at the operating points 
identified and how this relates to the best efficiency point (BEP) of the pump. 

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The pump and system curves cross at the best efficiency point. The pump has been matched to 
the system curve. 
The pump and system curves cross to the right of the best efficiency point. 
The pump and system curves cross to the left of the best efficiency point. 
Figure 3.14: Examples of pump and system curve variations 

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3.9 System calculations 
The calculated head at any given flow rate will be made up of static head and friction head, as 
explained below. 
The static head of a system is simply the difference in height between the input and the highest 
point. For long complex pumping schemes this may be more difficult to establish, but for simple 
designs of flood defence pumping stations this is usually very simple as the input and output are 
close together and readily accessible. In some cases, it is possible to gain some advantage by 
using the naturally occurring siphon effect of water passing over an enclosed pipe to reduce the 
overall effort required, in which case the static head is reduced. 
Friction head, sometimes referred to as ‘pipe losses’ is the equivalent head required to transfer 
the fluid through the pipes and fittings at the given velocity. 
Longer pipes with changes of direction, fittings and rough pipe surfaces tend to have higher 
friction losses than straight pipe runs (Wallingford, 1978).
Friction loss is also directly 
proportional to flow velocity, and hence it is important to increase pipe diameter as far as 
practicable to reduce the velocity. Generally, flow velocity of less than 1.0 m/sec is an ideal 
figure for pumping station design, although if the pipe run is very short this can be increased to 
over 2.0 m/sec. 
The pressure head of a system is only used where additional pressure is required at the 
delivery point, such as in water distribution systems. This is not applicable to flood defence 
applications. 
These factors are all added to determine the overall head for the system.