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November 2005: Fire Pumps

Fire pumps and fire booster pumps are critical pieces of equipment when it comes to providing an adequate fire protection water supply for many industrial and commercial properties. Fire pumps are needed at sites where public water supply pressure is insufficient to meet the automatic sprinkler system demand or where there is no public water supply at all. Where there is no public water supply at all, a fire pump and private water source (suction tank, reservoir, lake, or other) is needed. If the public water supply has sufficient flow available but not enough pressure, then a fire booster pump may be needed.

Typical centrifugal, horizontal fire pump (w/electric motor)
Typical centrifugal, horizontal fire pump (w/diesel engine)
Typical Vertical In-line Pump (w/electric motor)

 

Choosing the Right Pump Size

A fire pump should be selected in the range of operation from 90 to 140% of it's capacity. This means the total fire protection flow demand (sprinkler demand plus hose streams) should be equal to 90 to 140% of the pump flow rating.

For example, if the sprinkler system demand is 1,000 gpm and the hose stream demand is 500 gpm, then the total demand is 1,500 gpm. The fire pump should be rated for 1,000 to 1,667 gpm. Based on available pump sizes, the pump should be rated between 1,000 and 1,500 gpm.

The required fire pump pressure rating is governed by the maximum sprinkler system pressure demand. In the case of a booster pump, the available pressure from the public water supply at the demand flow is also factored in. As always, a suitable safety margin should always be included to account for possible future deterioration of the public water supply.

It is important to note that some property insurance companies and Authorities Having Jurisdiction (AHJ's) would prefer that the maximum demand point not exceed the rated capacity (100% of flow and pressure) of the fire pump.

In addition to sizing the pump according to the required fire demand, booster pumps must also be sized to the public water supply. A minimum of 20 psi pressure is recommended from the public water supply at 150% of the booster pump's rated capacity in order to help prevent pipe cavitation and possible damage to the fire pump and underground piping.

For example, if a booster pump is rated at 1,000 gpm, then the public water supply should be able to provide a minimum of 20 psi while flowing 1,500 gpm.

Generally, good design should dictate that the pump churn pressure plus static suction pressure not exceed the maximum pressure rating for system components, which is usually 175 psi. For fire pumps taking suction from tanks or reservoirs, such designs should be easily achievable. For booster pumps taking suction from public water supplies, such designs are achievable in most cases by the proper sprinkler system pipe sizing to minimize friction loss and the selection of a pump with a characteristic curve that most closely matches the system design requirements without causing excessive pressure under churn conditions.

Designs which intentionally incorporate the use of smaller diameter pipe and the use of a relief valve to truncate a portion or the water supply curve downstream from the fire pump should not be used!! As noted in NFPA 20, it is poor design practice to overdesign the fire pump and driver and then count on the pressure relief valve to open and relieve the excess pressure. A pressure relief valve is not an acceptable method of reducing system pressure under normal operating conditions and should not be used as such.

Besides those noted above, there are several factors involved in choosing and sizing fire pumps. Risk Logic can help you determine which is the right pump for your facility.

After a fire/booster pump has been installed, the pump and associated equipment requires regular testing and maintenance in accordance with manufacturer's recommendations and NFPA 25, "Inspection, Testing and Maintenance of Water-Based Fire Protection Systems."

The following is a summary of the recommended inspections, tests and maintenance as per NFPA 25:

NFPA 25, Table 8-1 Summary of Fire Pump Inspection, Testing and Maintenance
Item
Activity
Frequency
Pump House, Heating
Inspection
Weekly
Ventilating Louvers
Inspection
Weekly
Fire Pump System
Inspection
Weekly
Pump Churn Test
Test
Weekly
Pump Flow Test
Test
Annually
Mechanical Transmission
Maintenance
Annually
Electrical System
Maintenance
Varies
Controller Components
Maintenance
Varies
Motor
Maintenance
Annually
Diesel Engine System
Maintenance
Varies

Weekly Inspections

Pump House/Room Conditions

• Heat adequate, not less than 40°F (70°F for pump room with diesel pumps without engine heaters)

• Ventilating louvers free to operate

Pump System Conditions

• Pump suction and discharge, and bypass valves fully open

• Inspect for piping leaks

• Suction line pressure gauge reading normal

• System line pressure gauge reading normal

• Suction reservoir full

Electrical System Conditions

• Controller pilot light (power on) illuminated

• Transfer switch normal pilot light illuminated

• Isolating switch closed - standby (emergency) source

• Reverse phase alarm pilot light off or normal phase rotation pilot light on

• Oil level in vertical motor sight glass normal

Diesel Engine System Conditions

• Fuel tank two-thirds full (minimum)

• Controller selector switch in AUTO position

• Batteries (2) voltage readings normal

• Batteries (2) charging current readings normal

• Batteries (2) pilot lights on or battery failure (2) pilot lights off

• All alarm pilot lights off

• Engine running time meter reading

• Oil level in right angle gear drive normal

• Crankcase oil level normal

• Cooling water level normal

• Electrolyte level in batteries normal

• Battery terminals free from corrosion

• Water-jacket heater operating

Testing

NFPA 25 Section 8.3 - A weekly churn test of the fire pump shall be conducted. The test shall be conducted by starting the pump automatically (via the automatic starting mechanism) and running the pump a minimum of 10 or 30 min., for electric motor-driven and diesel engine-driven pumps respectively.

NFPA 25 Section 8.3.3 - An annual test of each pump assembly shall be conducted under minimum, rated (100%) and peak (150% rated) flows of the pump by controlling the quantity of water discharged through approved test devices. Pump discharge may be via hose streams or nozzles or via the bypass flowmeter if provided.

NFPA 25 Table 8.3.2.2 Weekly Churn Test Procedures

Pump System Procedures

• Record system suction and discharge pressure gauge readings

• Check pump packing glands for slight discharge

• Adjust gland nuts if necessary

• Check for unusual noise or vibration

• Check packing boxes, bearings, or pump casing for overheating

• Record pump starting pressure

Electrical System Procedures

• Observe time for motor to accelerate to full speed

• Record time controller is on first step (for reduced voltage or reduced current starting)

• Record time pump runs after starting (for automatic stop controllers)

Diesel Engine System Procedures

• Observe time for engine to crank

• Observe time for engine to reach running speed

• Observe engine oil pressure gauge, speed indicator, water, and oil temperature indicators periodically while engine is running. Record any abnormalities

• Check heat exchanger for cooling water flow

NFPA 25 Table 8.3.3.2 Annual Test Procedures

At No-Flow (Churn) Condition - conduct this test first

• Check circulation relief valve for operation to discharge water

• Check pressure relief valve (if installed) for proper operation

• Continue test for 10 min. (electric pump) to ½ hour (diesel pump)

At Each Flow Condition

• Record electric motor voltage and current (all lines)

• Record pump speed in rpm

• Record simultaneous (approximately) readings of pump suction and discharge pressures and pump discharge flow

• Observe operation of any alarm indicators or any visible abnormalities

Typical Pump Header

Flowmeters

Flowmeters are used in many installations as a convenient means of measuring flow. When installed, maintained and calibrated properly, these devices provide accurate, reliable flow data. Unfortunately, flowmeters can provide erroneous data if not installed and/or calibrated correctly. Flowmeters should not be installed in closed loop (recirculating) testing arrangements since they often provide poor test data and do not measure the true characteristics of the suction supply. In the closed loop arrangement, the suction supply pressure actually increases over the course of a flow test.

Typical Flowmeter

Water should be discharged (from the pump header, yard hydrants or other opening/nozzles downstream of the fire pump) at least every 3 yr. in order to calibrate the flowmeter.

Maintenance

NFPA 25 Section 8.5 - A preventive maintenance program shall be established on all components of the pump assembly in accordance with the manufacturer's recommendations. Records shall be maintained on all work performed on the pump, driver, controller and auxiliary equipment.

In absence of manufacturer's recommendations for preventive maintenance, alternative requirements are provided in Table 8.5.3 Summary of Fire Pump Inspection, Testing and Maintenance.

Alarms

NFPA 20 recommends the following alarms be provided for fire pumps and their related equipment:

• Fire Pump Running

• Fire Pump Power Failure (Loss of Power to Electric Motor)

• Fire Pump Failure to Start (Diesel Engine)

• Pump Controller not in Automatic Mode

• Diesel Engine Trouble (incl. Battery trouble, over speed, low oil

• Pump House Temperature

• Suction Tank Low Water Level

Typical Fire Pump Controller (w/ door open)

Typical Fire Pump Controller

Miscellaneous

Electrical Feed

The power supply for electric motor-driven fire pumps should be arranged in accordance with NFPA 20. The electric supply should be independent of the plant power supply or should be tied in ahead of the plant's electrical feed.

The pump circuit between its point of supply and the pump room should preferably be buried. However, when properly protected against damage by fire, wind, or lightning, it may be acceptable to locate this circuit: in a rigid steel conduit on the outside of an exterior wall of a fire-resistive building; in a conduit over or inside a fire-resistive building having a noncombustible occupancy; in messenger-supported cables or open wire over the roof of a fire-resistive building having a noncombustible occupancy; or overhead on poles in the plant yard where not exposed to potential damage from storage or operations.

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 10 psi less than the jockey pump stop point.

• The fire pump start point should be 5 psi less than the jockey pump start point. Use 10 psi increments for each additional pump.

• Where minimum run timers are provided the pump will continue to operate after attaining these pressures. The final pressures should not exceed the pressure rating of the system. It is our recommendation to remove run period timers and arrange fire pumps for manual shutdown only.

• When 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.

Typical Mercury Pressure Switch

At many facilities, a fire pump is the most critical single piece of fire protection equipment provided. Proper testing and maintenance of a fire pump can mean the difference of a small controlled fire or a major fire catastrophe. Risk Logic can answer any questions you have on the recommended inspections, testing and maintenance for your fire pump(s) and fire protection systems.