Fire water pumps are a critical part of sprinkler systems, standpipes and other fire suppression and safety equipment. They also need to meet NFPA regulations for inspection, testing and maintenance.
The most common type of fire pump is an electrical motor-driven unit. These take electrical power from a utility connection, generator or approved source to spin a shaft that moves the impellers.
Flow Rate
Every fire pump is rated for a specific flow rate at a certain pressure. It is important to understand the actual flow that a fire pump will see during normal operation or when testing a system. This information is based on the manufacturer’s performance curve and is typically available in the fire pump manual or on the nameplate attached to the fire pump.
During the hydraulic calculations it is essential to consider the net pressure (churn and demand) at the location where the fire pump discharge flange will be installed. This pressure is calculated by taking the consistent highest residual pressure at the water supply and subtracting the friction loss between the water source and the fire pump.
When selecting a fire pump, it is important to select one that is capable of meeting the demand flow and not going above the maximum allowable limit set forth in NFPA 20 Section 4.8.1. Typical manufacturers’ pump curves will go far beyond the rated flow, but it is important to be sure that the fire pump can meet demand without exceeding the allowable limit for a centrifugal fire pump.
Head
Fire sprinkler systems rely on pressure from the fire pump to operate. NFPA 20 sets out requirements to ensure that the system will work properly when it’s needed in an emergency.
The head of a fire water pump is the difference between the pressure at which it can discharge and its maximum rated pressure. It depends on the suction head and the discharge head, which are defined by the pump hydraulic design and vary along a performance curve with three limiting points: the shut-off point, the rating point and the overload point.
The power curve for a fire pump can either be constantly rising or peak and then begin to fall. When a pump’s power curve is climbing, it means that the motor is being undersized, violating UL and FM standards. When the power curve begins to peak and then fall, it’s being sized correctly.
Noise
A fire water pump is an essential component that handles the pressure demands of fixed-place systems like sprinklers and standpipes in commercial buildings. They’re also integrated into fire trucks and boats to boost their water supply for hose operations on the scene of an emergency.
The official decibel ratings that are published in the owner’s manual of a fire pump require laborious testing conducted under highly controlled conditions. A pump may seem louder in a building or setting compared to the standard rating because there’s a lot of variation in sound perception.
It’s possible to reduce noise from a fire water pump by preventing cavitation, which causes small vapor pockets in the flow of the water. This can cause damage to the pump because they implode and create holes in the impeller. To avoid this, be sure to select a pump that has a power curve that peaks and then begins to fall. Also, ensure that the pump is not elevated above the water source, which can increase the risk of cavitation.
Maintenance
Fire pumps can provide higher pressure for water-based fire suppression, and they are vital in protecting a facility. They must be properly inspected, maintained and tested to ensure they will work as intended in an emergency. This is done to satisfy building codes, comply with insurance requirements and most importantly protect people’s lives.
It is best for Owners to hire an independent contractor who specializes in fire pump testing because they have the expertise, tools and spare parts to conduct the tests to the highest standard. They also know the ins and outs of each fire pump, so they can quickly spot issues.
Some of the most important tests include weekly no-flow tests and annual full flow tests. These are performed by running the fire pump at rated speed for 30 minutes and allowing water to discharge through the pressure relief valve and casing relief valve. If the results of these tests do not match the original design specifications for churn and head, the system must be corrected before it is needed in a real emergency.
