Fire-pumps are typically listed by an approval institute and can be driven either by an electric motor or diesel engine. In a fire installation there can be one or more fire pumps put into operation as a duty assist (50%) – and standby pumps.
The fire-pump delivers the water via the pipe-system to the fire sprinklers to suppress the fire. Fire pumps are powered either by an electric motor or a diesel engine or sometimes by a steam turbine. The number of fire-pumps installed depends on the occupancy hazard (LH, OH or HH) and specific fire installation standard. Some known can be seen in the table to the right.
Where twin electric fire pumps are installed, there is a requirement for a secondary power source. This can be from a separate feed to the nearest electricity sub-station, or from a generator located on site. A mains changeover facility should be incorporated into the design to allow for switching to this alternate power source in the event of a mains supply failure.
The fire pump starts when the pressure in the fire sprinkler system drops below a certain set-point. If one or more fire sprinklers are exposed to heat above their design temperature, and opens, the sprinkler system pressure drops and the pressure switches gives a signal and the duty pump starts. If the duty-pump, for any reason, does not start, the standby pump will start, usually from a secondary pressure switch.
Types of pumps used for fire service include: end suction, horizontal split case, vertical split case, vertical inline and vertical turbines.
Most fire-pumps are listed for fire pump application, which means they are tested and certified by accredited laboratories and listed by authorized institutions such as VdS, UL, FM, LPCB etc. The main code that governs fire pump installations in North America is the National Fire Protection Association’s NFPA 20 Standard for the Installation of Stationary Fire Pumps for Fire Protection. The main code in Europe for fire pumps and fire sprinkler systems is BS EN 12845.
This is to keep the fire pump from running the entire time as well as ensuring the system stays in check.
It can also help prevent the system from damage when there is a fire and water rushes into the pipes. Jockey pumps consist of a three-part assembly.
Fire sprinkler systems consist of pipes with pressurized water in them and heads designed to open when they reach a certain temperature. When the particular temperature is reached and the heads open, the water pressure in the pipes drops to allow water to flow out. This action triggers the fire pump which will then begin to send more water through the pipes to enable the fire to be put out.
Now the jockey pump serves to keep the water pressure in the pipes within a specific range when there’s not a fire. This prevents the sprinklers from going off unnecessarily. Moreover, since pipes are susceptible to leakage over time, the water pressure inside them tends to go down. As soon as the jockey pump senses this, it fills them back up to normal pressure.
On the other hand, should the pressure drop drastically during a fire such that the jockey pump is unable to keep up, the large fire pump will be triggered to send out water for putting out the fire.
The jockey pump also prevents sprinkler systems from being damaged once the fire pump starts sending water. Lack of a jockey pump in a system for purposes of pressure maintenance will result in relatively low pressure. As such, the sudden change in pressure applied when the fire pump starts sending water is likely to damage the system.