Every boat through a canal lock spills water that someone must pump back
Each time a narrowboat works through a lock, a chamberful of water drains from the upper canal to the lower one, and most lock gates leak besides. Left alone, the top of a canal would slowly run dry. At Claverton in southern England, a river-powered waterwheel still drives pumps that lift water back up.
Pumping stations exist wherever water or sewage must go somewhere gravity will not take it. Canals are usually topped up by diverting streams into their highest stretches, but where no such source exists a station does the job. Claverton, on the Kennet and Avon Canal, draws from the River Avon using pumps turned by a waterwheel that the river itself drives. Other canals use back pumping, lifting water from below the bottom lock of a flight to the top, ready for the next boat. Claverton and Crofton are now preserved as museums.
Low land needs them too. Ditches can drain ordinary fields, but ground lying below sea level has to have its water lifted into channels that reach the sea, as in the Netherlands. Cities such as New Orleans rely on stations to clear water that leaks or floods into low-lying districts.
Sewage stations are the unglamorous workhorses. Waste flows downhill through sloping pipes into a pit called a wet well; when sensors detect a set level, pumps lift it through a pressurised main toward a treatment plant, or just to the next downhill sewer. Designers build in spare pumps so one failure does not cause an overflow, and use wide-passage pumps, or ones that shred solids, so rags and debris do not jam the impeller.
Those wells are dangerous places. Methane and hydrogen sulphide can collect inside and quickly overcome anyone who climbs in unprepared, so entry demands strict confined-space procedures. Older stations placed pumps in a separate dry chamber beside the well. Modern ones sink sealed submersible pumps straight into the sewage on guide rails, so they can be hoisted out for repair without anyone going down, and they have almost entirely replaced the old design.
Source: Pumping station
