Fire-pumps are typically made with non corrosive internal parts to avoid clogging due to corrosion. To avoid cavitation and to have a stable system pressure, the fire-pumps are most often designed specifically for fire-pump purposes, with strict demands to the NPSH value and flow [Q] and head [H] curve.
The fire-pump performance is very demanding regarding the ability to avoid cavitation and have a stable and continuous decreasing Head [H] with decreasing flow [Q]. The reason for these required characteristics are reliability and performance of water-distribution via the pipe-system and sprinklers into the building.
Since the fire-pumps are rarely in operation, except for testing, internal components should be made of non corrosive materials (stainless steel, bronze) to avoid the pump clogging or seizing.
NPSH-value (Net Positive Suction Head)
Fire-pumps have low NPSH-curves to avoid cavitation, causing decreasing flow and pressure. The NPSH curves are often measured up to 16 mtr. in order to decide the required power – but varies according to the different fire pump standards.
Q & H Curve (Flow Q and Head H curve)
Stable and continuous decreasing Q & H curves are desirable to achieve a stable system pressure, but also to have only one single point on the curve for each pressure point.
In cases where fire-pumps work in parallel, unstable fire-pumps would cause vibrations and could cause system breakdown. Fire pump standards define their own characteristics of the Q H –curves
Power Consumption Curve (P2)
Power consumption is measured as a function of head and flow. Power curves can be constantly increasing or with a local maximum point at the curve depending on the pump hydraulic design. Most curves have a constant rising power-curve. The power sizing for the fire-pumps vary from standard to standard but they all require adequate power reserves, either by selecting the driver size by end of the power curve or at NPSH-value = 16 m. for pumps with maximum flow at app. 5 m.
Maximum permissible flow (Qmax)
Maximum flow is mainly determined to avoid cavitations of the fire-pump and to ensure having enough power reserve, but in some cases also to dictate the capacity of the stored water.
For LPCB systems Qmax is determined in systems to dictate the capacity of the stored water (60 minutes on OH and 90 minutes on HH).