The Diesel Driven Fire Pump and NFPA 20

The diesel driven fire pump is mainly used for automatic sprinkler fire extinguishing systems and fixed fire water supply occasions in industrial and mining enterprises, engineering constructions, high-rise buildings and other civil occasions. It is characterized by advanced technology, high degree of automation, reasonable structure, simple installation and excellent cost performance.

NFPA 20 requires that backup fire pumps be fueled by an alternate source of power when the height of a building exceeds the capability of fire department pumps or the normal power supply is not reliable (e.g., blackouts, fires). This source of power is often a diesel or steam-driven fire pump.

In order to prevent over-pressurization in a stand-by fire protection system, these engines are designed with a constant speed drive and engine controls configured to maintain set pressures. This is accomplished by limiting the rate of fuel flow to the engine to achieve a constant speed and by applying an engine throttle governor in the event of an emergency.

Unfortunately, this approach is not without problems. Consider, for example, a design of a 12-sprinkler system for which the initial system-demand flows are calculated to be 2,160 gpm at 98 psi. When this system is initially activated, however, only one or two sprinklers may open, resulting in lower initial system-demand flows. Consequently, the fire pump driver and engine will typically produce pressures well in excess of the 98-psi design pressure rating.

Fortunately, the NFPA 20 Technical Committee is open to change and has recently approved the use of devices capable of reducing the engine speed automatically to prevent over-pressurization in occupied spaces. This is an enormous step forward and a testament to the willingness of this group to put aside commercial interests and embrace change.