Fire pumps are critical for most water-based fire protection systems, particularly in high-rise buildings and structures. When the water source does not have enough pressure to supply the system, its main job is to increase the water pressure. This article will review the operation and different types of fire water pumps.
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Working Principle of Fire Water Pump
A fire water pump comprises two parts: a driver and a controller. Each pump operates on one of the two following principles:
- Centrifugal Pumps
- Positive Displacement Pumps
Centrifugal fire water pumps generate centrifugal forces by rotating the impeller and throwing water from the centre to the outer parts of the impeller. On the other hand, positive displacement fire water pumps take a predetermined amount of liquid as input and use mechanical action to displace it through the outlet. They generally use pistons, gears, vanes, lubes, and similar devices to increase liquid pressure while discharging.
Centrifugal fire water pumps are used for high flow rates to provide a constant water flow, primarily for buildings, utility stations, and other similar applications. Positive displacement fire water pumps are ideal for non-water applications like foam concentrate or water mist systems.
A fire sprinkler system’s fire pump typically draws water from an underground water supply or a water tank, lake, or reservoir. These pumps run on either electricity or diesel fuel. The fire pumps’ high-pressure aids in properly distributing water through the sprinkler system and hose standpipes.
Types of Firewater Pumps
Depending on the working philosophy mentioned above, there are two main types of fire water pumps: centrifugal and positive displacement. These fire pumps can be further classified into the types listed below.
Centrifugal Fire Water Pumps
The most common type of fire pump is a centrifugal fire pump. They have a large water capacity. The following are the most common sub-types of centrifugal fire pumps:
Split-Case Pumps, Horizontal and Vertical
Horizontal Split Case Pumps are extremely dependable fire pumps with long lifespans and a wide range of sizes. They come in various rated flow and pressure capacities, making them suitable for various firewater applications. The flow is divided into a horizontal split-case pump and enters the impeller from opposite sides of the pump housing. The pump has a split casing (hence the name), allowing easy access during pump maintenance. A horizontal shaft connects the pump to the driver.
Vertical Turbine Pumps
Vertical turbine pumps are permitted in fire water systems under the NFPA 20 fire protection pump standard. They can start with negative pressure and accept water from a below-grade source. They are available in various pressures and capacities, with either diesel or electric motors.
In-line Pumps
In-line pumps are commonly used when space is limited. They can have vertical or horizontal shafts, but vertical shafts are more common. Vertical in-line fire pumps ensure that water flows smoothly throughout the system. This type of fire pump has a low initial cost but is costly to repair. They have a limited capacity and can only be used with an electric driver.
End Suction Top Discharge Pump
The discharge of an end suction fire pump is perpendicular to the suction inlet. They are smaller and take up less space than horizontal split-case fire pumps but have limited capacity. End suction fire pumps can be driven by either an electric or a diesel engine.
Multistage Multiport Pump
Multiple impellers in series in a single casing drive a horizontal shaft in multistage Multiport fire pumps. Multiple discharge outlets in the casing deliver fluids at varying pressures. Pressure increases with each successive series impeller. They can be powered by either an electric or a diesel engine.
Fire Pumps with Positive Displacement
Positive displacement fire pumps generate very high pressures but have a limited flow volume compared to centrifugal fire pumps. They are classified into two types: reciprocating and rotary. Positive displacement fire pumps are rarely used and are only found in specialized applications such as water mist and foam-water systems.
Fire Pump Features
The following are the main characteristics that a fire pump should have:
- Internal pump components must be made of non-corrosive materials.
- The pump must be selected based on the required NPSH value, flow, and heat demand to avoid cavitation.
- Every fire pump must have a sufficient power reserve.
