Engineering Considerations for Stationary Fire Pump Installations

Proper design ensures that fire protection water supplies remain available, stable, and verifiable throughout the life of the system.

By Sahil Mahajan, PE, P.Eng, CPD, LEED Green Associate

NFPA 20 establishes the minimum engineering requirements for the selection and installation of stationary fire pumps supplying liquids for private fire protection, including their associated power supplies, controls, and acceptance testing.

Centrifugal pumps must deliver at least 100 percent of rated flow at rated pressure, not less than 150 percent of rated flow at a minimum of 65 percent of rated pressure, and a shutoff (churn) pressure typically limited to 140 percent of rated pressure unless components are rated for higher pressures. These performance criteria underpin both pump selection and acceptance test evaluation using certified factory curves.​

Centrifugal Fire Pump Capacities

Centrifugal fire pumps must be sized so the highest single system demand (the most demanding sprinkler or standpipe calculation tied to that pump) does not exceed 150 percent of the pump’s nameplate flow. Pumps are to be selected from standardized capacities and must provide at least a minimum specified net pressure (40 psi or 2.7 bar). Very large pumps above approximately 5,000 gpm (18,925 L/min) are not covered generically; they require case‑by‑case acceptance by the authority having jurisdiction (AHJ) or a listing organization.

In terms of practical application, using a pump beyond roughly 140 percent of its rated flow is discouraged because performance becomes highly sensitive to suction conditions, and using it below about 90 percent of rated flow is also not recommended due to less-favorable efficiency and stability. This does not prevent the pump from operating anywhere along its characteristic curve—from shutoff up to 150 percent of rated capacity—provided the suction conditions are adequate; rather, it means the intended design operating point should sit in the more reliable central portion of that curve.

Pressure Maintenance (Jockey or Makeup) Pumps

Pressure maintenance pumps in NFPA 20 are intended to keep the fire protection system pressurized under normal, non‑fire conditions so the main fire pump does not start for small leaks or minor pressure fluctuations.​​ This can be a jockey pump, a suitable water‑mist positive-displacement unit, or another approved arrangement such as a domestic system pump in a dual‑purpose supply, provided it can reliably maintain fire system pressure.​

Pressure maintenance pumps are not required to be listed. Pressure maintenance pumps shall be approved as per NFPA 20. They must be sized to:

1. Make up allowable leakage and normal pressure drops in the system.
2. Have a rated capacity at least equal to the expected normal leakage rate.
3. Develop enough discharge pressure to hold the desired system pressure.​​

The NFPA 20 annex stresses that sizing depends on the system type and extent: pumps serving large underground mains must be larger than those serving only aboveground piping because NFPA 24 allows some leakage from buried mains, while new aboveground systems should be effectively tight.​

For systems serving only aboveground sprinkler/standpipe piping, size the jockey pump so its flow is less than a single sprinkler’s flow. That way, an open sprinkler will drop pressure enough to start the main pump, not be fully carried by the jockey. A commonly used rule of thumb is a pump that can make up allowable leakage in about 10 minutes, with not less than approximately 1 gpm (3.8 L/min) for small systems; many designers also use about 1 percent of the fire pump’s flow at a slightly higher pressure as a practical target.

The annex also notes that a centrifugal jockey pump is generally preferable for stable pressure characteristics and that its suction can be taken from a tank fill line so system pressure can be maintained even if the fire tank is temporarily drained for maintenance.​​

Because the jockey pump controls system pressure, its pressure-sensing line must be installed like a fire pump controller sensing line (i.e., proper materials, taps between check and isolation valves, and correct small orifices for damping).​​ This ensures accurate pressure feedback and avoids nuisance cycling or failure to start the main pump when real flow occurs.

Fire Pump Operation

NFPA 20 describes fire pump operation as follows:

Motor-Driven Pump

To start a motor-driven pump, the following steps should be taken in the following order:

1. Ensure that the pump is completely primed.
2. Close the isolating switch and then close the circuit breaker.
3. An automatic controller will start the pump if system demand is not satisfied (e.g., pressure low, deluge tripped).
4. For manual operation, activate the switch, pushbutton, or manual start handle. A circuit breaker tripping mechanism should be set so it will not operate when the current in the circuit is excessively large.

Diesel Engine-Driven Pump

To start a diesel engine-driven pump, the operator should be familiar beforehand with the operation of this type of equipment. The instruction books issued by the engine and control manufacturer should be studied to this end. The storage batteries should always be maintained in good order to ensure prompt, satisfactory operation of this equipment (i.e., check electrolyte level and specific gravity, inspect cable conditions, corrosion, etc.).

Fire Pump Settings

The fire pump system, when started by pressure drop, should be arranged as follows:

• The jockey pump stop point should equal the pump churn pressure plus the minimum static supply pressure.
• The jockey pump start point should be at least 10 psi (0.68 bar) less than the jockey pump stop point.
• The fire pump start point should be 5 psi (0.34 bar) less than the jockey pump start point. Use 10 psi (0.68 bar) increments for each additional pump.
• Where minimum-run timers are provided, the pumps will continue to operate at churn pressure beyond the stop setting. The final pressures should not exceed the pressure rating of the system components.
• Where the operating differential of pressure switches does not permit these settings, the settings should be as close as equipment will permit. The settings should be established by pressures observed on test gauges.

Examples of fire pump settings follow. (For SI units, 1 psi = 0.0689 bar.)

• Pump: 1,000 gpm, 100 psi pump with churn pressure of 115 psi
• Suction supply: 50 psi from city-minimum static; 60 psi from city-maximum static
  • Jockey pump stop = 115 psi + 50 psi = 165 psi
  • Jockey pump start = 165 psi – 10 psi = 155 psi
  • Fire pump stop = 115 psi + 50 psi = 165 psi
  • Fire pump start = 155 psi – 5 psi = 150 psi
  • Fire pump maximum churn = 115 psi + 60 psi = 175 psi

Automatic Recorder

The performance of all fire pumps should be automatically indicated on a pressure recorder to provide a record of pump operation and assistance in fire loss investigation.

Very Tall Buildings (420 ft and above), Backup Fire Pump/Alternate Means

For zones “partially or wholly” beyond fire department pumping capability, NFPA 20 requires additional redundancy on the pumping side.​ The options are:​

• Provide fully independent and automatic backup fire pump units arranged so that all zones can remain in full service with any one pump out of service (i.e., N+1 capacity for the overall vertical system).
• Provide an auxiliary means capable of delivering the full fire protection demand, acceptable to the AHJ (for example, alternate gravity‑fed tank arrangements with enough head or other engineered solutions).
• An auxiliary means can also be in the form of pumping through the fire department connection in series with the low- or mid-zone fire pump as approved by the AHJ as noted in NFPA 14.

This requirement recognizes that for very tall buildings, firefighters cannot rely on exterior apparatus and hose lines to substitute for a failed building pump.

When trying to determine the pumping capability of the fire department, the concern is the height of the building. Some buildings are so tall that it is impossible for the fire department apparatus to pump into the fire department connection at the street and overcome the elevation loss and friction loss to achieve 100 psi at the hose outlets up in the building. In these cases, the fire protection system in the building needs to have additional protection, including sufficient water supplies within the building to fight a fire and sufficient redundancy to be safe. Since fire departments all purchase different apparatus with different pumping capabilities, NFPA 20 addresses this concern with performance-based criteria rather than a specified building height. Most urban fire departments have the capability of getting sufficient water at sufficient pressure up to the top of 200 ft (61 m) tall buildings. Some have the ability to get water as high as 350 ft (107 m). The design professional will need to check with the local fire department to determine its capability.

Fire Pumps Arranged in Series

A series fire pump installation must operate as a single coordinated system, including pumps, drivers, controllers, and accessories. Within 20 seconds after a demand to start, pumps in series shall supply and maintain a stable discharge pressure (±10 percent) throughout the entire range of operation. The discharge pressure shall be permitted to restabilize whenever the flow condition changes. The entire system must be field-tested to confirm proper performance.

Pumps are generally required to be located in the same fire pump room. Separate rooms are permitted only if operators can control all pumps from any room, see all suction and discharge pressures, receive alarms from the other rooms, and communicate between rooms. A series arrangement is limited to three pumps maximum, with no more than two variable-speed pumps. Pumps cannot automatically shut down due to suction pressure. Pressure-reducing or regulating valves cannot be installed between pumps. Maximum pressures at shutoff must remain within each pump’s pressure rating.

Interconnecting control wiring between rooms must be protected from fire and physical damage similarly to fire pump power wiring. The supply (lower zone) pump must start if the remote start control circuit opens. Controllers must comply with applicable controller performance requirements.

Each pump room must display the operating status of pumps located in other rooms using audible and visual indicators. Required signals include pump running condition, electrical or controller trouble, power supply conditions, and low suction pressure for both electric and diesel pumps. Controllers must also provide remote monitoring contacts unless equivalent communication is provided.

When pumps are in separate rooms, a survivable two-way emergency communication system must connect the rooms to coordinate operation during emergencies.

Drivers, Controllers, and Power Supply Arrangements

NFPA 20 sets strict, reliability‑focused requirements for how electric‑motor and diesel‑engine fire pumps are driven, controlled, and powered.​​

Electric Fire Pump Drivers and Power Supply

• The motor must be suitable for across‑the‑line starting at its rated voltage and frequency and sized so it can deliver the full pump load at rated speed without exceeding its nameplate current when the power system is within allowable voltage tolerance.​​
• The normal electrical supply must be highly reliable and typically comes as a dedicated feeder or service that is not shared with non‑fire loads, routed to minimize exposure to fire, and limited in the number and type of disconnecting means permitted ahead of the fire pump controller.​​
• Voltage drop between the source and the controller is restricted so the motor can start and run at locked‑rotor current without excessive undervoltage; feeder and conductor sizing must consider starting current as well as running load.​​
• Where required for high‑rises or by the AHJ, a separate alternate source (usually an onsite generator) must be arranged so transfer to the alternate source does not interrupt or trip the pump and so the alternate source and transfer equipment are protected and sized specifically for fire pump duty.​​

Electric Fire Pump Controllers

• Controllers must be listed for fire pump service, factory assembled and tested, and marked with manufacturer, ratings, and enclosure type.​​
• They must start the pump automatically on a drop in system pressure, on operation of associated fire‑protection equipment (such as deluge or dry‑pipe valves, where arranged), and on certain remote manual signals, and they must also allow local manual starting that bypasses any automatic control failures.​​
• Overcurrent protection integral to the controller is specially timed: it must allow the motor to ride through locked‑rotor current long enough to start, and it must not trip on inrush while still providing protection against prolonged faults; upstream overcurrent devices are limited so they cannot inadvertently stop the pump.​​
• Controllers must provide visible and audible indication of key conditions locally (pump running, power loss, phase reversal or failure, controller trouble, engine or motor faults, as applicable) and also be capable of providing contacts for remote monitoring by the fire alarm or supervisory system.​
• Automatic weekly test functions are required: the controller must periodically start the pump (typically via a solenoid‑driven pressure drop), run it for the programmed duration, and then shut it down, with this activity recorded on the pressure recorder.​

Diesel Fire Pump Drivers

• Diesel engines used as fire pump drivers must be listed for this service and capable of driving the pump at rated speed and load over the expected ambient temperature range and fuel conditions.​​
• Each engine must have two independent starting energy sources (typically two separate battery sets with their own chargers), wired so the controller alternates on successive automatic starts and can crank for a defined total time if the engine fails to start immediately.​​
• The fuel system must provide a minimum duration of operation at rated load (often eight hours by local practice), with protected fuel tanks, piping, strainers, and valves located to minimize fire exposure; automatic fuel maintenance systems are addressed so fuel quality is maintained over time.​​
• Engine cooling, exhaust routing, combustion air, and room ventilation must be designed for full‑load heat rejection while keeping room temperatures and exhaust backpressure within engine limits, and exhaust outlets must discharge to safe outdoor locations.​

Diesel Engine Controllers

• Diesel fire pump controllers, like electric controllers, must be listed, factory assembled, and tested and installed close to and in sight of the engine they control, in enclosures suitable for a damp mechanical room environment.​
• They must automatically start the engine on low system pressure, on operation of connected fire‑protection equipment, and on remote start signals, and they must include a fixed “attempt‑to‑start” sequence with multiple crank intervals separated by rest periods.​​
• The controller must supervise and annunciate a wide range of engine conditions such as low oil pressure, high coolant temperature, failure to start, overspeed shutdown, battery failure, charger failure, low fuel, and low cooling or starting air pressure where applicable, with audible and visible alarms locally and contacts for remote indication.​​
• Automatic shutdown is tightly limited (for example, permitted after an overspeed trip or during weekly test when no other start cause is present); otherwise, once started by a demand condition, the engine must continue to run until intentionally shut down by an operator in accordance with the procedures.​

Common Pump Room and Wiring Arrangements

• For both electric and diesel installations, drivers and controllers must be located in a protected pump room with adequate clearances, environmental control, and drainage and wired so external control circuits cannot prevent a required start; faults in external circuits are allowed to force the pump to run but not to stop or block starting.​​
• Pressure‑sensing lines for pressure‑actuated controllers must be installed in corrosion‑resistant metallic piping from the discharge line (between check and isolation valves), with specific check/union arrangements and test valves to ensure accurate, testable sensing and to avoid accidental shutoff.​

Together, these requirements ensure that whether the driver is an electric motor or a diesel engine, the fire pump has a robust, fault‑tolerant power supply, a controller designed to prioritize starting and continued operation, and a monitored, testable control system that aligns with the broader fire alarm and emergency power infrastructure.

Acceptance Testing, Documentation, and Troubleshooting

NFPA 20 outlines hydrostatic testing, flushing, field acceptance performance testing, and documentation requirements that complete the engineering cycle from design to commissioning. Key elements include:​

• Flushing and hydrostatic testing of suction and discharge piping prior to performance tests, documented using NFPA contractor’s material and test certificates
• Flow testing at churn, rated, and 150 percent of rated capacity, with simultaneous measurement of suction and discharge pressures and, for electric drives, voltage and current
• Comparison of test points to the certified factory pump curve, including speed corrections, and evaluation of any deviation from rated performance

NFPA 20 requires record drawings, test reports, manuals, special tools, and spare parts to be turned over to the owner, with ongoing inspection, testing, and maintenance governed by NFPA 25.

Conclusion

Properly sized main and jockey pumps, associated piping and appurtenances, coordinated pressure settings, and carefully designed pump rooms, controls, and acceptance tests work together to ensure that fire protection water supplies remain available, stable, and verifiable throughout the life of the system.

References

• NFPA 20: Standard for the Installation of Stationary Pumps for Fire Protection
• NFPA 14: Standard for the Installation of Standpipe and Hose Systems

About the Author

Sahil Mahajan, PE, P.Eng., CPD, LEED Green Associate, has a Master of Science in Mechanical Engineering and is currently working at KEA Engineers in Iselin, New Jersey, as the Plumbing and Fire Protection Department Head. He has nearly 20 years of experience in HVAC, plumbing, and fire protection design and is a licensed Professional Engineer in the United States and Canada.

The opinions expressed in this article are those of the authors and not the American Society of Plumbing Engineers.