A Diesel Fire Pump is the power source that drives a fire water supply system in high-rise buildings when an electrical motor cannot be supplied with sufficient power from the building emergency generator. It is a very important component in these systems and must be properly designed, evaluated and installed. NFPA 20 requires that an alternate or backup source of power be provided for this application.
Most of the time, this is accomplished by using an emergency generator that has been sized to provide the required starting in-rush current as well as all other emergency loads while still meeting the maximum voltage drop allowed during these conditions at the fire pump motor. The sizing of the generator can be a complex task to ensure that the power requirements for the fire pump are adequately met.
Another issue often overlooked is that of cooling the engine. This is particularly important for a diesel engine fire pump driver because it utilizes water to cool the engine. The water is pumped through the engine heat exchangers from the fire line piping. This water must be available to the engine at all times or it will overheat and damage the engine.
In order to avoid damage to the engine, it is essential that the exhaust system be sized correctly. This can be done with a computer program that will help to ensure that the back pressure on the engine is not too high and that it will not impact available power at the fire pump motor. The system must also be insulated and protected to prevent the transfer of heat to the fire pump room or other locations in the building.