Feed water pumps are almost exclusively centrifugal pumps which convey the necessary feed water to a steam generator (the boiler in conventional power stations and boiling water reactors or the pressure generator in pressurized water reactors). The feed-water pumps (full-load, half-load pumps etc.) used in conventional power stations are multistage pumps with sectional or pot-type housings; in nuclear power stations (as main feed and backing or booster pumps) they are almost exclusively single-stage, dual flow designs with a double scroll housing.
Feed-water pumps are powered by either turbines or electric motors. Typical operating data:

• Powers up to 30 MW (in rare cases up to 50 MW), depending on the block size of the power station
• Delivery rates (mass flows) up to 4,000 t/h
• Discharge pressures up to approximately 400 bar at temperatures up to around 200 ° C
  

• Pressures of up to approximately 40 bar at the mechanical seals
• Speeds from 4,500 to 6,000 rpm
• Sliding velocities between 40 and 65 m/s at the mechanical seals.

In multistage feed-water pumps, axial movements of the shaft (shaft displacement) of between ± 3 mm arise and have to be compensated by the mechanical seal. Mechanical seals are employed almost without exception for main, full-load or half-load pumps. Stuffing box packings (now found only occasionally in backing pumps) and floating ring seals are hardly ever used any longer.