Feed‑water pumps are classified into high‑pressure and low‑pressure types primarily based on their outlet operating pressure. The fundamental reason is to match boiler equipment of different pressure ratings. Meanwhile, differences in pump‑set configurations in large‑scale power plants further distinguish high‑ and low‑pressure working conditions.
Low‑pressure feed‑water pumps generally operate at an outlet pressure ≤ 1.6 MPa. Most adopt a single‑stage or few‑stage impeller structure, featuring low head, simple construction and low sealing requirements. They are mainly applied to atmospheric‑pressure and low‑pressure small‑size steam boilers as well as hot‑water heating boilers. These pumps only need to overcome routine resistance from pipelines and boiler bodies to deliver feed water, and the working medium is mostly ambient‑temperature water.
High‑pressure feed‑water pumps normally achieve pressures ranging from 10 MPa to 35 MPa, with even higher pressures under supercritical unit conditions. They employ a multi‑stage boosting structure with more than ten impellers to generate ultra‑high head through pressure buildup across successive impellers. Equipped with dedicated high‑pressure sealing and balancing assemblies, such pumps serve high‑temperature high‑pressure utility boilers and large‑scale industrial high‑pressure boilers. Given the extremely high steam pressure inside high‑pressure boilers, feed‑water pressure must exceed the internal boiler pressure to force water into boiler drums and water‑wall tubes for normal equipment operation.
Large thermal power plants adopt a combined high‑ and low‑pressure pump‑set arrangement. As low‑pressure‑side equipment, the low‑pressure booster pump draws water from the deaerator storage tank and performs preliminary pressure rise, supplying stable inlet pressure for the main high‑pressure pump and effectively preventing cavitation in the latter. The main high‑pressure pump takes discharge water from the booster pump, raises pressure further and delivers feed water to the boiler, acting as the core high‑pressure output component of the system.
Interchange between high‑pressure and low‑pressure feed‑water pumps is strictly prohibited. A low‑pressure pump cannot provide sufficient head to supply water for high‑pressure boilers, which may lead to boiler water cutoff and tube rupture failures. Conversely, the excessive pressure of a high‑pressure pump surpasses the pressure‑bearing rating of low‑pressure equipment, readily causing overpressure rupture of pipelines and boilers and posing severe safety hazards. Furthermore, high‑pressure pumps incur higher energy consumption, capital cost and maintenance expenditure; deploying them for low‑pressure service results in substantial resource waste.
In short, the high‑/low‑pressure classification of feed‑water pumps essentially matches pump head to boiler pressure‑bearing requirements. The dual‑pump configuration in power plants forms a supporting high‑and‑low‑pressure operating system, representing a professional setup that balances equipment safety, operational efficiency and energy costs.