A boiler feedwater pump is a specific type of

pump A pump is a device that moves fluids (liquids or gases), or sometimes Slurry, slurries, by mechanical action, typically converted from electrical energy into hydraulic or pneumatic energy. Mechanical pumps serve in a wide range of application ...

used to pump

feedwater Boiler feedwater is the water which is supplied to a boiler. The feed water is put into the steam drum from a feed pump. In the steam drum the feed water is then turned into steam from the heat. After the steam is used, it is then dumped to the ...

into a

steam boiler file:Dampfkessel für eine Stationärdampfmaschine im Textilmuseum Bocholt.jpg, An industrial boiler, originally used for supplying steam to a stationary steam engine A boiler or steam generator is a device used to create steam by applying heat ...

. The water may be freshly supplied or returning condensate produced as a result of the condensation of the steam produced by the boiler. These pumps are normally high pressure units that take suction from a condensate return system and can be of the

centrifugal pump Centrifugal pumps are used to transport fluids by the Energy transformation, conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow. The rotational energy typically comes from an engine or electric motor. They are ...

type or positive displacement type.

Construction and operation

Feedwater pumps range in size up to many kilowatts and the

electric motor An electric motor is a machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a electromagnetic coil, wire winding to gene ...

is usually separated from the pump body by some form of mechanical coupling. Large industrial

condensate pump A condensate pump is a specific type of pump used to pump the condensate (water) produced in an HVAC (heating or cooling), refrigeration, condensing boiler furnace, or steam system. Applications Condensate pumps may be used to pump the conde ...

s may also serve as the feedwater pump. In either case, to force the water into the boiler, the pump must generate sufficient pressure to overcome the steam pressure developed by the boiler. This is usually accomplished through the use of a centrifugal pump. Another common form of feedwater pump runs constantly and is provided with a minimum flow device to stop overpressuring the pump on low flows. The minimum flow usually returns to the tank or deaerator.

Failure of mechanical seal

Mechanical seals of boiler feedwater pumps often show signs of electrical corrosion. The relative movement between the sliding ring and the stationary ring provokes static charging which is not diverted due to the very low conductivity of the boiler water (below one micro-Siemens per cm �S/cm. Within short periods of operation – in some cases, only a few hundred operational hours – pieces having the size of fingertips break off from the sliding and/or the stationary ring and cause rapid increases in leakage current. Diamond-coated ( DLC) mechanical seals avoid this problem and extend durability remarkably.

Steam-powered pumps

Steam locomotive A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, Fuel oil, oil or, rarely, Wood fuel, wood) to heat ...

s and the

steam engine A steam engine is a heat engine that performs Work (physics), mechanical work using steam as its working fluid. The steam engine uses the force produced by steam pressure to push a piston back and forth inside a Cylinder (locomotive), cyl ...

s used on ships and stationary applications such as

power plant A power station, also referred to as a power plant and sometimes generating station or generating plant, is an industrial facility for the electricity generation, generation of electric power. Power stations are generally connected to an electr ...

s also require feedwater pumps. In this situation, though, the pump was often powered using a small steam engine that ran using the steam produced by the boiler. A means had to be provided, of course, to put the initial charge of water into the boiler (before steam power was available to operate the steam-powered feedwater pump). The pump was often a positive displacement pump that had steam valves and cylinders at one end and feedwater cylinders at the other end; no crankshaft was required.

Duplex steam pump

A duplex steam pump has two sets of steam and water cylinders. They are not physically connected but the steam valves on the first pump are operated by the movement of the second pump's piston rod, and vice versa. The result is that there are no "dead spots" and the pump is always self-starting.

Jet injector

An injector pump uses the

Venturi effect The Venturi effect is the reduction in fluid pressure that results when a moving fluid speeds up as it flows from one section of a pipe to a smaller section. The Venturi effect is named after its discoverer, the Italian physicist Giovanni Ba ...

and steam condensation to deliver water to a boiler.

References