Fire Fighting Water Pumps
Fire fighting water pumps are an essential component in most fire protection systems. Understanding their value and characteristics is important to the facility owner, the Authority Having Jurisdiction (AHJ) and fire safety professionals.
A jockey pump maintains pressure in the header at a set level, which turns on the main pumps when necessary. The firefighting water pump is then connected to the hydrant via large-diameter hose.
Types
There are many different types of fire fighting water pumps, each with their own strengths and weaknesses. For example, single-stage volute casing pumps, double-suction radial flow pumps and ring-section pumps all extract water at high pressure from tanks or fire water ponds to supply fire suppression systems.
Horizontal split case pumps are the most popular fire pumps because they are economical for high water flow applications, easily accessible for maintenance and have long lifespans. They are available in a variety of sizes to meet any fire suppression system’s needs.
Drencher pumps, on the other hand, are designed to be mounted above a building’s windows and roof openings. These pumps require more powerful and robust water pressure to push the water into a room with a high occupancy level, and they are typically used in larger buildings. The two main considerations when choosing a fire pump are PSI and GPM. PSI refers to the pressure per square inch that the pump can exert, while GPM is the number of gallons of water it can move in one minute.
Flow Rates
The amount of water in gallons per minute (GPM) is what extinguishes the fire and keeps firefighters safe on the fireground. The fire fighting water pump’s gpm rating is important to know in order to choose the right hoselines and nozzles for the job.
Most pumps are advertised with their rated pressure at churn and their rated flow. However, this information can be misleading when it comes to selecting a fire fighting water pump for the application. It is essential to review the manufacturer’s performance curve and look at the pump’s pressure rating at a specific flow rate, such as the demand of a standpipe system.
When a fire pump is specified to supply a standpipe system flow demand, the pressure at churn should be less than 140 psi and the maximum pressure for operation must not exceed 150 percent of the pump’s rated flow. It is also important to understand the friction loss values that the Denver Fire Department assigns to their appliances to help prevent overpressure.
Hose Sizes
When it comes to sizing fire fighting water pumps, the hose size is important. In most municipal fire departments, a 1.5″ hose is utilized (though 2″ hoses are also used). A proper sized hose will be manageable for firefighters and match the discharge port size of the pump.
Suction hoses connect fire trucks to water sources like hydrants and must be able to withstand vacuum pressures that occur when a nozzle is attached. Supply hoses convey water over long distances, such as from one hydrant to another or to the fire truck pump that keeps attack hoses charged with water. These hoses must be able to handle high water pressures, but they don’t need to bend as often as attack hoses.
The threading on fire hoses is called NH or NST, and it cannot be connected to a standard PVC, metal or galvanized steel pipe. The hoses are sealed with couplings that have an internal diameter that’s slightly larger than the outside diameter of the hose.
Safety
Fire fighting water pumps are a critical component to putting out fires. This is why they need to be properly installed, tested and maintained by a fire protection engineer.
The pump casing should be designed for ease of disassembly, allowing the impeller to be inspected without disturbing the suction piping. The pump should also be rated to resist the effects of cavitation. This can be caused when liquid pressure falls below vapor pressure, creating small vapor pockets that implode and damage the pump components.
NFPA 20 outlines specific requirements for the operation of a fire pump including the type of motor, the driver and how often the fire pump should be inspected and tested. These measures ensure that fire pumps will be able to perform their essential functions when called upon.
MPOs take pride in knowing their apparatus, identifying the correct flow pressure for each pre-connected hand line on their truck at a moment’s notice, and taking full control of the panel while on scene.