What is a Fire Pump? Working, Sizing, and Types of Fire Pumps

To understand how a Fire Pump functions, one must first distinguish it from a standard domestic or industrial water transfer pump. While a standard pump is designed for efficiency and longevity under continuous load, a Fire Pump is an emergency standby unit engineered for “reliability at all costs.” Its primary objective is to deliver a specific volume of water at a high enough pressure to overcome the friction loss of the piping and the elevation of the building, ensuring that fire suppression heads (sprinklers) function effectively.

The system operates on a pressure-sensing logic. The fire protection piping is kept pressurized by a smaller “Jockey Pump.” When a fire occurs and a sprinkler head opens, the system pressure drops. The Fire Pump controller detects this drop via a sensing line. If the pressure falls below the “start” setpoint, the main Fire Pump driver (electric motor or diesel engine) activates. Once running, the pump draws water from a reliable source—such as a suction tank, reservoir, or municipal water main—and accelerates it using centrifugal force to increase its kinetic energy, which is then converted into static pressure at the discharge volute.

A critical aspect of the Fire Pump working principle is its performance curve. Unlike other pumps that might have a steep decline in pressure as flow increases, a fire-service-listed pump must have a “relatively flat” curve. This ensures that even if more sprinklers open than originally calculated, the system can still provide at least 65% of its rated pressure while flowing at 150% of its rated capacity. This “over-capacity” buffer is the fundamental safety margin required by global engineering standards.

• Pressure Sensing Lines: Always use brass or stainless steel for sensing lines. Plastic or galvanized lines are prone to corrosion and clogging, which can prevent the Fire Pump from starting automatically when a fire occurs.
• Room Ventilation: For diesel-driven units, the air intake and exhaust ventilation are just as critical as the fuel supply. Many Fire Pump engines stall during prolonged operation because they “suffocate” in poorly ventilated mechanical rooms.
• The Jockey Pump Myth: Never size your jockey pump too large. If the jockey pump can meet the demand of a single sprinkler head, the main Fire Pump may never start, leading to a dangerous delay in high-pressure suppression.
• Weekly Run Tests: In 2026, automated testing is common, but nothing replaces a manual check for leaks at the packing glands and verifying the cooling water discharge for diesel engines.