Fire pumps are needed when the local municipal water system cannot provide sufficient pressure to meet the hydraulic design requirements of the fire sprinkler system. This usually occurs if the building is very tall, such as in high-rise buildings, or in systems which require a relatively high terminal pressure at the fire sprinkler in order to flow a large volume of water, such as in storage warehouses. Fire pumps are also needed if fire protection water supply is provided from a ground level water storage tank. Fire pumps may be powered either by an electric motor or a diesel engine, or, very occasionally a steam turbine.
The fire pump is designed to start when pressure in the fire sprinkler system drops below a threshold. The sprinkler system pressure drops significantly when one or more fire sprinklers are exposed to heat above their design temperature, and opens, releasing water or alternatively when other firefighting connections are opened, causing a pressure drop. Types of pumps used for fire service include: horizontal split case, vertical split case, vertical inline, vertical turbine, and end suction. A jockey pump is a small pump connected to a fire sprinkler system in parallel with the fire pump.