Fire pumps are a critical component of a building's sprinkler system in settings where the water supply is insufficient to provide the pressure needed to keep the water flowing to all the sprinkler heads. Fire pump intakes are connected to underground public water supply piping, or a tank or reservoir located onsite, to provide water flow at a higher pressure to the sprinkler system risers and hose standpipes.
Fire pumps are activated when the water pressure in the system drops below a certain threshold. For example, this can happen when one or more of the sprinkler heads are exposed to heat exceeding the temperature they were designed for or when other firefighting connections are opened, causing pressure in the mainline to fall.
While trained fire protection professionals must perform the design and installation of fire pumps, this post will provide an overview of the different types of fire pumps in use today and summarize the factors considered when choosing a pump.
Does Your Sprinkler System Require a Fire Pump?
Not all sprinkler systems require a fire pump. However, those installed in most commercial buildings do because the pressures needed to ensure adequate flow to all parts of the system usually exceeds what a standard public water supply can provide. When the sprinkler system is connected to a static water source, a fire pump is always required.
If your building doesn't have a fire pump and annual testing of your existing sprinkler system reveals a pressure issue, you may be required to install one, depending on the nature of the problem.
Because fire pumps are an integral part of so many sprinkler systems, there are many sections of the National Fire Protection Association (NFPA) 13 Standard for the Installation of Sprinkler Systems that reference them (e.g., pump room requirements, testing, etc.).
However, the requirements pertaining specifically to the actual design and installation of fire pumps are found in the National Fire Protection Association (NFPA) 20 Standard for the Installation of Stationary Pumps for Fire Protection. In addition, if your system is supplied with an onsite tank, you will find additional requirements for their installation and maintenance in NFPA 22 Standard for Water Tanks for Private Fire Protection.
Different Types of Fire Pumps and their Applications
Positive Displacement Pumps
Positive displacement pumps create flow pressure by repeatedly capturing a fixed volume of water into the pump's internal chamber using suction to compress it before releasing it out of the discharge valve. These pumps are not as common because their flow volume is more limited than that which centrifugal pumps can provide and are typically only used with water mist or foam-water systems.
Centrifugal Pumps
Centrifugal fire pumps are the most common type of pump used in commercial buildings today. This type of pump creates pressure through centrifugal force with an internal impeller. When the pump is activated, water flows into the center of the impeller, which rotates at high speed to drive the water to the discharge valve creating pressure by pushing high volumes of water through the valve. There are several different types of centrifugal pumps, which are described below in terms of some considerations that might factor into the selection of a fire pump for your building.
|
Centrifugal Pump Type |
Driver Type(s) |
Key Considerations |
|
Horizontal Split-Case |
Electric or Diesel |
● Highly reliable ● Easy to maintain (pump is located in a separate casing in front of the motor) ● Larger than most other types of pumps (requires more space) ● Available in a wide range of rated flow and pressure capacities ● Must be mounted on a concrete housekeeping pad ● Diesel-driven pumps come with additional requirements |
|
Vertical Inline Pumps |
Electric-only |
● More difficult to maintain (motor is located above the pump must be lifted to gain access) ● Less susceptible to mechanical damage from water turbulence ● Slim profile (fits into smaller spaces) ● Can be mounted on pipe stand supports ● Limited capacity (usually 1,500 GPM*) |
|
Vertical Turbine Pumps |
Electric or Diesel |
● Typically used to pull water from sources below the pump such as a lake or pond, wells, or underground tanks ● Available in a wide range of rated flow and pressure capacities ● Diesel-driven pumps come with additional requirements |
|
End Suction Pumps |
Electric or Diesel |
● More compact than horizontal split-case pumps (requires less installation space) ● Limited capacity (usually 1,500 GPM) ● Diesel-driven pumps come with additional requirements |
|
Multistage Multiport Pumps |
Electric or Diesel |
● May require fewer pumps and less piping (potential cost and space savings) ● High capacity, ideal for high-rise buildings ● Can eliminate the need for water storage tanks on higher floors ● Diesel-driven pumps come with additional requirements |
*gpm = gallons per minute
Choosing the Right Type of Pump Driver
The most common types of fire pumps in use today are electric motor-driven and diesel engine-driven fire pumps.
Electric-driven pumps are always preferable where possible because electric motors are more compact and require fewer mechanical parts, making them very cost-effective. They also have fewer negative environmental impacts. Electric-driven pumps can run off a utility connection, a generator, or other power source approved by your AHJ.
Diesel-driven pumps are typically used where the power grid is unreliable or unable to handle the load of an electric-driven pump. They are also used where there is a lack of emergency power available, such as a generator.
You can expect more regulations for diesel-driven pumps than electric pumps due to the extra steps necessary to handle the fuel system, cooling, exhaust, vibration, etc. For example, diesel-driven pumps require additional space for fuel tank storage and must be located in a separate enclosure or room with direct access to the exterior.
How Fire Pumps are Sized
The size of the fire pump needed is usually determined during the design of a sprinkler system. When designing a sprinkler system, a hazard analysis must first be conducted to determine the occupancy classifications, which are defined based on the expected fire hazards in different spaces within the building. This analysis determines the number of sprinkler heads required. And, while the number of sprinkler heads served is an important factor to consider in sizing a fire pump, the size required is based on the most hydraulically demanding area of the entire sprinkler system, which may or may not be the area with the most sprinkler heads.
Determining the most hydraulically demanding area in the system is a highly complex calculation that requires qualified fire protection professionals to conduct. Factors that go into calculating it include:
- Distance — The building's footprint will determine how far water must travel laterally to reach the farthest sprinklers.
- Elevation — The designer must take into account how many floors the building has. Due to the effects of gravity, more pressure will be required to push water to sprinklers on higher floors.
- Occupancy Classification — It is important to know if there are hazards within the building that might require more water to suppress a fire and where they are. This is why the hazard analysis must be conducted before sizing the fire pump.
Correctly sizing the fire pump is made even more difficult because units expressed in GPM cannot be directly converted into PSI. Thus, while the capacity of the sprinkler system is defined in terms of gallons per minute (GPM) -- the amount of water flowing through the system, fire pumps are typically sized by pressure range, pounds per square inch (PSI).
Questions About Fire Pumps?
If your building currently uses a fire pump or needs one, it's also important to consider the inspection and testing requirements for them. At Koorsen, our factory-trained and certified technicians make complying with fire pump requirements easy. We can handle all the inspection and testing required for your sprinkler systems, including the fire pumps, and help you maintain and repair them when needed to keep your entire system in peak condition. With 75 years in the business, Koorsen is a leader in the fire protection industry and has engineers available to answer any questions you might have about fire pump design and installation. Contact Koorsen today to learn more!