How to Size a Fire Water Pump

The fire water pump delivers water at the proper pressure and flow to fight fires. This requires high quality design and manufacturing technology.

It is important to understand the sizing process for fire pumps based on the sprinkler system demand and pressure. This will ensure the pump is sized correctly for the system.

Hydraulic Pressure

The most demanding area of the fire protection system is usually the standpipe. Unlike sprinklers, a standpipe requires pressure from the fire department pumper truck in order to supply its demand for water, so it is important to determine the expected demand of this most demanding area before attempting to size a fire pump.

It is also necessary to evaluate the available water supply for the site. Whether the water is from a municipal supply, on-site storage or a natural body of water the type and amount of raw water is a major driver for what type of fire pump is needed to meet the expected demand of the hazard.

A good starting point is to look at the manufacturer’s performance curve for each model fire pump. This will show how much net pressure the pump produces at various flow conditions between churn and its rated flow. If the power curve peaks and then begins to fall, it is likely that the pump has been undersized.

Energy Efficiency

The hydraulic pressure generated by city supply lines is not typically high enough to support the fire water demand of sprinklers and standpipe systems. Installing a fire water pump provides a boost in pressure which helps to meet the building’s hydraulic demand.

A fire pump must be tested annually under no-flow (churn) and rated capacity load conditions. These annual tests are conducted by a certified tester who must also verify the churn and rated capacities of the controller.

The driver of the fire pump, whether electric motor or diesel engine, must be sized to match the horsepower demand as shown on the factory-certified test curve. If not, the fire pump may not be operating to its full potential, and it could also be in violation of UL and FM requirements.

Another important factor to consider is the internal marine growth on the pump intakes and components, such as Asian clams and zebra mussels. These organisms clog intake points and reduce performance. One way to combat this is by using a flame-plated impeller, which contains tungsten carbide on the wear surfaces. This unique coating outwears hard chrome plating, tool steel and even stainless steel.

Life Expectancy

The working life expectancy of fire pumps is heavily dependent on a number of factors. For example, the quality of the water used will have a major impact. For instance, using chlorinated water will corrode the steel components in the pump. The temperature and humidity in the pump room will also have a significant effect. The more moisture there is, the faster a pump will wear down.

Another factor that impacts fire pump life is the frequency of maintenance and testing. This is especially important because the hydraulic performance of the pump may degrade over time.

For example, if a fire pump fails to meet the required minimum test flow rate during a routine performance test, it will require replacement. New rules have been introduced to help address this issue by adding provisions based on the fire department’s pumping capabilities and providing additional redundancies. In addition, the flushing requirements for suction piping have been revised.

Maintenance

Like any mechanical system, a fire water pump needs to be regularly tested and maintained by a trained professional. This will ensure that it operates as needed to help protect people and property when a fire occurs.

This will include a visual inspection of the fire pump and components to verify that it looks in working condition with no visible physical damage. The battery, internal engine, and controller should also be tested. This includes a no-flow test to make sure the fire pump starts and runs without water, and a flow test to ensure it meets its intended design capacity.

Routine maintenance runs are required to lubricate the packing glands as well as to check and adjust them. If this is not done, the glands will corrode and can cause severe damage to the pump shaft. These maintenance runs can also be a good time to clean the drain lines so that they don’t become clogged.