What Is Fire Pump Priming and When Is It Required?

Fire pumps are essential components of fire protection systems, designed to provide adequate water pressure during a fire emergency. However, to operate effectively, certain types of fire pumps—particularly centrifugal fire pumps—must be primed before use. Failing to do so can result in pump failure, system downtime, or reduced water flow during critical moments.

In this article, we explain what fire pump priming is, why it matters, the types of fire pumps that require priming, and when and how priming should be done, in accordance with NFPA 20 and general industry best practices.

What Is Fire Pump Priming?

Fire pump priming is the process of removing air from the pump casing and suction line and filling it with water so the pump can function correctly. Centrifugal fire pumps, which rely on a spinning impeller to create pressure and move water, cannot pump air. If the pump casing is filled with air rather than water, the impeller will spin without creating the necessary suction—this is known as air binding.

Priming ensures that the impeller has water to work with, allowing it to create the necessary pressure differential to draw water in and discharge it through the fire protection system.

Why Is Priming Important?

Priming a fire pump is not just a matter of operational efficiency—it’s a matter of life safety. A fire pump that fails to deliver water in an emergency can result in:

• System failure

• Inadequate fire suppression

• Potential property damage

• Loss of life

• Violation of NFPA 20 compliance

Unprimed pumps are particularly dangerous in manual or standby pump systems where startup occurs only during emergencies. If priming isn’t done in advance, there might not be enough time to correct the issue during a fire event.

Types of Fire Pumps and Priming Requirements

Not all fire pumps require priming. The need for priming depends largely on the type of fire pump and the system design.

1. Centrifugal Fire Pumps (Horizontal or Vertical Split Case)

These pumps require priming unless they are installed in a flooded suction configuration (i.e., the water source is above the pump). If installed above the water source, they must be primed either manually or through an automatic priming system.

2. Vertical Turbine Fire Pumps

Vertical turbine pumps are self-priming by design because the impellers are submerged in water, typically installed in wells or tanks. The pump column is always filled with water, so air does not get trapped inside the casing.

3. End Suction Fire Pumps

Like horizontal split-case pumps, these pumps require priming if they are not installed below the water level. End suction pumps are often used in compact systems and are more susceptible to air binding if not properly primed.

4. Positive Displacement Pumps

Some positive displacement fire pumps (used for foam systems or special applications) may also need priming, especially if air is present in the suction line. However, their ability to move air allows for limited operation without priming.

When Is Fire Pump Priming Required?

Priming is generally required in the following conditions:

1. During Initial System Startup

Before a newly installed system is commissioned, centrifugal pumps must be primed to remove air that may have entered during installation.

2. After Maintenance or Repairs

If the fire pump or suction line is opened for repairs or inspection, priming is needed before the pump can operate again.

3. If the System Is Not Flooded

If the pump is located above the water source (non-flooded suction), regular priming is essential before each use.

4. Post-Testing or Draining

Priming is necessary after routine fire pump testing or after the system is drained for any reason.

Methods of Fire Pump Priming

There are several methods used to prime fire pumps:

1. Manual Priming

Technicians use a manual priming pump or vacuum device to remove air and draw water into the pump casing. This is common for testing or initial startup.

2. Automatic Priming Devices

Some systems are equipped with automatic priming devices, such as vacuum pumps, air ejectors, or automatic air release valves, that ensure the pump is always filled with water.

3. Flooded Suction Arrangement

In this setup, the water supply is always higher than the pump, so the pump stays primed without intervention. This is the preferred NFPA-compliant configuration to avoid priming altogether.

NFPA Guidelines for Fire Pump Priming

The NFPA 20: Standard for the Installation of Stationary Pumps for Fire Protection outlines best practices for fire pump installations. It recommends:

• Avoiding installations that require priming whenever possible.

• Using flooded suction configurations to ensure the pump is always filled with water.

• Installing air release valves on top of the pump casing to allow trapped air to escape.

• Ensuring priming mechanisms (if used) are reliable and tested regularly.

Common Priming Problems and How to Avoid Them

Even with proper procedures, some issues can prevent successful priming:

1. Air Leaks in Suction Line

Small leaks in suction piping can prevent full priming. Ensure joints are sealed properly.

2. Blocked Foot Valve

If using a foot valve in non-flooded systems, make sure it is clean and not blocked by debris.

3. Dry Running

If the pump runs without water, it can overheat and be damaged. Always verify priming is successful before activating the pump.

4. Improper System Design

Avoid designs where priming is needed but not supported by equipment or procedures.

Fire Pump Priming in Emergency Scenarios

During a fire emergency, there is no time for manual priming. For this reason, flooded suction systems or reliable automatic priming is essential in real-world applications. Regular testing and preventive maintenance are the only ways to guarantee the fire pump will function properly when it's needed most.

Maintenance Tips to Ensure Proper Priming

• Inspect suction piping and valves regularly.

• Test air release valves to ensure they’re working.

• Keep all priming devices clean and functional.

• Perform regular pump tests under NFPA 25 guidelines.

• Verify water levels in tanks and reservoirs.
  
  

Conclusion

Fire pump priming is a small but critical part of a fully functional fire protection system. Understanding when it is required and ensuring the correct method is in place can mean the difference between effective fire suppression and a failed response in an emergency.

At Better Technology Group, we specialize in manufacturing reliable fire pumps that meet international standards such as UL, FM, and NFPA 20. Our team can help you choose the right pump configuration—whether you need flooded suction or priming-ready systems—to ensure your fire protection infrastructure performs when it matters most.