WA ST E WAT E R
Pump failure contingencies in action at Sydney Water By Paul White, Team Leader - Program Management and Technical Support, Sydney Water
Sydney Water operates and maintains 680 Sewerage Pumping Stations (SPS) and 164 Water Pumping Stations (WPS) in the Sydney, Blue Mountains and Illawarra areas. It is one of the world’s largest operator of pumping stations, reflecting the hilly terrain of the Sydney Basin, particularly on the coastline and rivers.
T
he early types of pumping stations were mainly of ‘conventional’ type (horizontal or vertical centrifugal pumps with coupled motors, or dry submersible-type pumps) housed in a dry well with an outer wet well for a SPS or on a platform next to a reservoir for a WPS. Apart from the conventional type pumping stations there are also different types of SPS’s. There was SPS
‘ejector’ types using compressed air to push sewage up the SPS pressure main, but these became obsolete and all have been replaced. Sydney Water was the first in Australia to use ’vacuum’ SPS’s in low, flat, high-water table areas that uses a vacuum to suck sewage from small pits located near houses and taken to the SPS. However, the majority of current SPS’s are of a ‘submersible’ type, using pumps located within a circular wet well to pump the sewage up the pressure main. The size of these pumping stations varies enormously from small of only a few litres per second pumped to large stations pumping many hundreds of litres per second. Typically, an SPS has two pumps (one duty and one standby) whilst a WPS will have two to four pumps (one to three duty and the remainder standby). The stations are unmanned and can be in remote locations. The pumps are the most important equipment of the pumping station, with its function to pump the water or sewage from a low collection point to a higher discharge point like a water reservoir or a sewerage trunk main. The stations have in normal circumstances redundancy in that if the duty pump fails then the standby pump will automatically takeover the pumping duty. Failure is detected using IICATS (a 24/7 telemetry alarm and control system). If the standby pump does not start (due to a fault, is already offline for repairs, there is supply power failure) then there is a period of detention time. Detention time is the capacity of the wet well and incoming
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sewerage main matched against the sewage inflow (inflow varies considerably at different times of the day) for a SPS. For a WPS it is the water reservoir capacity matched against customer water consumption. Detention time is the period before sewage overflow or loss of water supply will occur to allow a breakdown response crew to attend the pump failure and effect repair. Sydney Water has installed at a large number of pumping stations additional safeguards such as emergency storage tanks to greatly increase detention time, on-site gas powered emergency bypass pumps, on-site electrical generators or dual power supplies. If the pump fault repairs are likely to exceed available detention time, and there are no additional safeguards, then Sydney Water declares an Incident and implements the most appropriate contingency action to avoid sewage overflow or a loss of water supply. There are different types of contingency action for pump failures and each pumping station needs to be assessed for the most suitable action to be implemented. All the pumping stations in Sydney Water have site specific contingency plans that contain relevant technical details (pump head, inflow and required pumped flow rate, pump motor KW rating, pump type/model number and relevant drawings), if bypass pump fittings are installed, the nominated tanker collection/discharge points, suitability for mobile generator connection