ABSTRACT
The most common fire pump in use is the electric-driven, horizontal shaft, single-stage, centrifugal pump. This pump type is readily arranged for automatic operation. The horizontal split-case pump is noted for its generous water passages, efficient operation, and easy access to all working parts. The water flow enters at one or both sides of a bronze disc (called the impeller) from the suction inlet in the pump’s casing. Power from an electric motor is directly transmitted to the pump through the shaft, which rotates the impeller at very high speeds. This rotation drives the water by centrifugal force to the discharge outlet. It is the action of the centrifugal force that provides the added pressure. “While centrifugal pumps remain the most common pump used for fire protection purposes, other types, such as positive displacement pumps, are also available and now addressed by the standard. In fact, Chapter 5 of NFPA 20 consists entirely of new information specifically addressing positive displacement pumps, which operate by discharging a set volume of water during each pump shaft revolution through a mechanical means, such as a piston plunger or rotary gear. Positive displacement pumps are most commonly used to pump foam concentrate into a foam system and for water mist systems that require very high pressures.” [1] Fire pumps must be directly coupled to the electric motor (or diesel engine) driver. Fire authorities around the globe do not allow anything other than a direct-drive unit. The only pumps that are allowed to be driven through a speed-increasing gearbox are the vertical turbine pumps.
