Project: sc090025/R1

Figure 3.19: Example of typical siphonic recovery pump system layout 
3.15 Sump model tests 
The importance of the intake and sump design in the overall pumping station efficiency should 
not be underestimated. Efficiency losses in excess of 15 per cent may be experienced for a 
poorly designed sump. The difficulty in existing pumping stations is identifying the characteristic 
signs, on the surface of the water of problems, such a swirls, vortices uneven flow and so on 
due to their enclosed nature. Some indications, such as high/low current or noise from within 
the pump, may be present, but the actual causes will be difficult to pinpoint as will any remedial 
works. 
On larger stations it is recommended that model tests are carried out before major 
refurbishment or new works are undertaken. Although these are often viewed as unnecessary 
project expenditure, given the well-established sump design manuals available, they can 
identify serious problems with the sump proposals and the solutions before any works are 
undertaken. 
 
 
 
 
 
 
 
 
 
 
 
 
 
Figure 3.16: Sump mmodel for an Environment Agency refurbishment project 
 

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3.16 Pre-swirl at pump intakes 
Most pumps are designed for rotation free inflow. Rotational flow will therefore cause the 
internal flow inside the pump to depart from the design pattern and cause the performance of 
the pump to deviate from design parameters. Hence, pre-swirl rotation should be avoided or 
kept within limits prescribed by the manufacturer. 
Rotational flow usually arises from an asymmetrical velocity distribution at the entry to a sump 
which results in the development of rotational momentum which is then amplified as flow 
converges into the pump intake.