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Fire pumps are the key and indispensable components of many water-based fire protection systems, such as sprinklers, risers, foamed water, water sprays and water mist, and are suitable for a wide range of commercial and industrial applications. If it is determined to be necessary through hydraulic analysis or other purposes, the fire pump installation provides the water flow and pressure required by the fire fighting system. Without a properly designed and installed fire pump, the fire protection system cannot be expected to achieve its goals.
This article reports on some of the key changes in the 2013 edition of the NFPA 20 Standard for Installation of Stationary Pumps for Fire Protection, which was released in the summer of 2012. Pump and fire pump installation requirements and the role of NFPA in establishing these requirements.
Overall, NFPA 20 received 264 amendment proposals, 135 official follow-up comments, and 2 successful on-site actions at the NFPA 2012 Las Vegas Technical Report Conference.
Fire pumps, whether they are centrifugal pumps or positive displacement fire pumps, are specifically listed, and the standards have been revised to make it clear that only fire pumps can be used for fire fighting. The previous edition was aimed at “other pumps”, whose design features were different from those specified in the standard, and allowed such other pumps to be installed in the locations listed in the testing laboratory. However, since all electric pumps are classified as electrical equipment, some people interpret this provision as allowing any electric pump to be used as a fire pump. This was not intended, and the language was revised to better clarify this point.
In order to facilitate review and approval by the competent authority (AHJ) and other stakeholders involved in the installation of fire pumps, new regulations on design details and drawings have been added. The standard will now require related plans to be drawn on a uniform size drawing in accordance with the specified scale. In addition, the plan now includes specific details about the various features of the overall installation, such as details related to pump manufacturing, model and size, water supply, suction piping, pump drives, controllers, and pressure maintenance pumps.
If a water flow test is used to determine whether the water supply to the fire pump is adequate, NFPA 20 now requires that the test be completed no more than 12 months before the work plan is submitted, unless otherwise permitted by the AHJ. Some people worry that, in some cases, old test data that does not accurately reflect the current status of the water supply is used as a design basis for the selection of fire pumps. In this case, when the water supply is actually lower than the amount indicated by the old test data, the acceptance test may indicate that the discharge pressure of the pump is lower than the calculated value and is insufficient to meet the needs of the entire system. Water supply assessment and testing are complex, require understanding of the layout and operation of the water system, and can only be completed by competent personnel.
Pump rooms and independent pump rooms that contain fire pump equipment require special protection, as listed in NFPA 20 in the form of a table. One of the entries in the relevant table refers to pump rooms and pump rooms that are not sprayed with water. Some readers of NFPA 20 misinterpreted the title, which means that NFPA 20 allows the omission of sprinklers in such spaces in buildings that require or are considering the use of sprinkler systems. Added consultation language to clarify that the purpose of the “Unsprinkled” heading in the table is to determine the fire protection type of the fire pump in the unsprinkled building-that is, the pump room needs to be separated from other buildings and the building is constructed in 2 hours, or the pump room needs a distance The building served by the pump room is at least 50 feet tall. The purpose of this heading is not to provide an exception for the omission of sprinklers in the fire pump room of a building that is completely sprinkled.
NFPA 20 provides protection for fire pump equipment and those who need access to fire pump equipment in the event of a fire. Although NFPA 20 requires the fire department to plan the access to the fire pump room in advance, it now also requires the location of the fire pump room to be planned in advance. In addition, NFPA 20 requires that pump rooms that cannot be directly accessed from the outside of the building provide a closed passage from enclosed stairs or external exit doors to the pump room. The previous version of NFPA 20 required the passage to have a fire resistance rating of at least 2 hours.
The 2013 revision requires the passage to have the same fire resistance rating as the pump room; that is, in a fully sprinkled building including the pump room, the passage only needs 1 hour of fire resistance. The fire resistance level of the passage leading to the pump room does not have to exceed the requirements of the fire pump room. If the fire pump room and passage are built as a separate direct connection area, the passage will basically become a part of the fire pump room, and only need to divide the room with the same fire resistance level as the fire pump. Please note that additional terms on this subject apply to high-rise buildings.
In order to minimize the turbulence at the suction flange, NFPA 20 specifies the nominal size of the suction pipe based on the capacity of the fire pump. These specified pipe sizes are based on a maximum flow rate of 15 feet per second at 150% of the pump’s rated capacity. Users of NFPA 20 will notice that this clause has been removed from the standard body and added to the table as a footnote. Some users of the standard incorrectly interpret this speed information as a verification condition during pump acceptance testing. Rather, the purpose of including this information is to provide some background knowledge about the origin and development of prescribed suction tube dimensions.
Unless certain conditions are met, NFPA 20 requires the arrangement of the suction piping to ensure that there is no negative pressure at the suction flange of the pump. The centrifugal fire pump is not suitable for lifting or pulling water towards its suction flange. The requirement that the suction pressure at the suction flange is not less than 0 psi applies to installations composed of a single pump unit and installations composed of multiple fire pump units intended to operate together. The amendment to this clause clarified that for multiple pump installations, only those pumps that are designed to operate simultaneously are considered when assessing suction pressure conditions. Some users of NFPA 20 have misunderstood this requirement and include redundant pumps or those that only run when the main pump is stopped. This is not the intention of the clause.
The existing exception to the positive pressure requirement at the suction flange specifically allows -3 psi suction pressure. This exception applies to the case where the fire pump is running at 150% of the rated flow while pumping from the ground storage tank. The attachment text for this exception has been revised to target all types of centrifugal fire pumps, not just those horizontal fire pumps. Other amendments to the attachment text indicate that at the end of the required water flow duration, if the pump suction chamber height is equal to or lower than the water level in the storage tank, a margin of -3 psi suction pressure reading is allowed. The previous version refers to the elevation of the pump room floor and tank bottom. The revised text better ensures that no lift or tension will occur between the water tank and the suction flange of the fire pump. As currently stated in the appendix, when the pump is running at 150% capacity and the water in the tank is at the lowest level, the -3 psi suction pressure margin accounts for the friction loss in the suction pipe.
Certain devices in the suction pipeline can cause undesirable levels of flow and turbulence, and hinder pump operation and performance. NFPA 20 currently stipulates that within 50 feet of the pump suction flange, no valves can be installed in the suction pipe except for the listed external stem and yoke (OS&Y) valves. This clause was revised to clarify that, with the exception of the listed OS&Y valves, no “control” valves may be installed within 50 feet. This clause was further revised to specifically target reflow equipment. These changes provide better consistency with other provisions of the standard and clarify the intent of the requirements, that is to restrict the use of butterfly valves only, and allow the installation of OS&Y gate valves, check valves and return devices in the suction pipeline. But please note that only in other The installation of check valves and backflow devices in the suction pipeline is only permitted under conditions required by standards or AHJ. If a check valve or backflow prevention device is required upstream of the suction port of the fire pump, the NFPA requires the device to be at least 10 pipe diameters upstream of the pump suction flange.
Fittings such as elbows, tees and cross joints in the suction pipe will cause the water flow into the pump to be unbalanced. The imbalance occurs where the fitting changes the flow plane relative to the flow plane through the fire pump. This unbalanced flow will reduce the performance and service life of the pump. NFPA 20 restricts the location and arrangement of such fittings in the suction piping. Such pipe fittings should not be installed within 10 pipe diameters of the suction flange. The current exception to this rule allows the centerline plane of the elbow to be perpendicular to the horizontally split pump shaft at any position of the pump suction port. This elbow arrangement does not create harmful flow conditions. For the next version, this exception has been extended to include T-shirts.
When the fire pump sucks from the bottom of the storage tank, NFPA 20 requires certain arrangements for the discharge of the storage tank. When water flows out from the outlet of the water tank, vortexes are often formed, introducing air into the suction pipe and increasing the occurrence of turbulence. A similar phenomenon occurs when water is drained from the sink or bathtub. As mentioned earlier, turbulence and unbalanced flow into the suction port of the pump should be avoided.
In order to prevent this phenomenon, NFPA 20 requires the use of devices that prevent the formation of eddy currents. This device is often incorrectly referred to as a vortex plate, but the terminology in NFPA 20 has been revised to better correlate with NFPA 22 (Standard for Private Fire Water Tanks) and to clarify that the device is actually a “vortex plate “” A plate used to prevent vortex formation. In addition, a reference to the Hydraulic Association’s “Centrifugal Pump, Rotary Pump, and Reciprocating Pump Standard” has been added to the attachment text for more information on the subject.
Since the 2003 edition, NFPA 20 allows the use of low suction throttles where AHJ requires a positive pressure in the suction line. The purpose of this type of valve is to help ensure that the pressure in the suction pipe does not drop to a predetermined critical level due to available water supply conditions. For example, when a municipal water supply main is used as the water supply for a fire protection system, the main may not provide as much water as the fire pump can pump, especially when the pump is operating under near overload conditions. The resulting pressure drop in the municipal main can lead to undesirable conditions, such as groundwater or backflow contamination, or in extreme cases can cause the main to collapse.
If the AHJ requires the use of a low suction throttle valve, NFPA 20 requires that such a throttle valve be installed in the discharge line between the pump and the discharge check valve. The sensing line connected to the suction pipe controls the position of the throttle valve. When the suction pressure drops to the preset throttling pressure (usually 20 psi), the valve starts to close, thereby restricting the flow and maintaining the suction pressure at the preset level.
When water flows through the throttle valve, friction loss will occur, which needs to be considered in the system design. The frictional losses associated with these devices can be significant. For example, flow through 8 inches. The equipment may cause a pressure drop of up to 7 psi. Although the current version contains advisory text for this situation, the 2013 version will force the design of the fire protection system to consider the friction loss through the low suction throttle valve in the fully open position.
NFPA 20 requires monitoring the test outlet control valve in the closed position. As mentioned earlier, this regulation may be incorrectly interpreted as meaning the monitoring of the valves on the outlets of the various hose connections connected to the test header manifold. This is not the intent of the standard. It is clearly stipulated that the control valve in the pipeline between the discharge pipe and the hose valve test header manifold needs to be supervised in the closed position; the external valve on each outlet of the test header does not need to be supervised.
The previous regulations that required a gap of not less than 1 inch around pipes passing through walls or floors have undergone major changes. The scope of the regulations is reduced to include only the walls, ceilings and floors of the fire pump room enclosure. It solves the use of other gaps, pipe sleeves and flexible joints, and provides better relevance to the requirements of NFPA 13, the installation standard for sprinkler systems.
The term “pressure relief valve” is usually applied to large valves that are sized to discharge large amounts of water from the discharge port of a fire pump. The use of this valve is limited to specific applications. The term “circulation pressure relief valve” refers to a small pressure relief valve used to discharge a small amount of water for cooling when no water is discharged downstream of the fire pump. Motor and radiator cooling diesel engine centrifugal fire pump requires a circulation safety valve between the fire pump discharge port and the discharge check valve. An additional circulating pressure reducing valve is required downstream of the pressure reducing valve, which returns to the suction port through a pipe. When the meter test loop returns to the suction port of the fire pump through the pipeline, an additional circulation safety valve is also required.
The regulations on the pressure relief valve have been rearranged to make it clearer that the pressure relief valve is only allowed to be used when the following “abnormal” pump operating conditions cause the system components to bear pressures exceeding their pressure ratings: (1) Diesel engine pump drive 110 % Rated speed operation, (2) the electric variable speed voltage limiting controller runs across the line (rated speed).
NFPA 20 allows the discharge of the pressure relief valve to be sent back to the suction pipe through the pipe. A new regulation in the 2013 edition concerns a pump driven by a diesel engine that integrates heat exchanger cooling for the engine. For this arrangement, the 104 F high cooling water temperature signal from the engine inlet of the heat exchanger water supply will be sent to the fire pump controller. After receiving this signal, if there is no effective emergency signal requesting the operation of the fire pump, the controller will stop the engine.
The recirculation of the water discharged from the pump back to the pump suction pipe can cause problems because the recirculated water is not only used to cool the engine, but also to cool the engine intake air temperature. The cooling of the engine intake air temperature is critical to meeting the engine emission requirements of the US Environmental Protection Agency. Temperatures in the range of 150 F have been observed. Although there may be enough water flow to adequately cool the engine at these elevated temperatures, the intake port temperature cannot be adequately cooled and may cause the engine to operate outside of the EPA-compliant range. Although the pressure relief valve opens only under overpressure conditions, and a circulating pressure relief valve should also be installed to help maintain the water temperature, this additional precaution was developed to ensure compliance with the wider concerns related to fire pumps.
In the 2010 edition, the concept of tandem fire pump units was introduced, and a fire pump unit arrangement aimed at unified operation was described, that is, the first pump directly sucks water from the water supply, and each sequential pump sucks water from the previous water source. Pump. This type of series unit is most common in high-rise buildings and other large buildings and structures. In the first two revision cycles, including the 2013 edition, the Fire Pump Technical Committee spent a lot of effort to review the regulations for the arrangement of tandem fire pump units.
The central issue is related to the location of the fire pump unit. In the past two cycles, it has been suggested that all the pumps that constitute the arrangement of the series fire pump unit should be placed in the same fire pump room. For the 2013 edition, an exception was made to allow fire pump installations to be located in different rooms under certain conditions. Although this language passed the review of the Fire Pump Committee, it was returned at the NFPA Association Technical Meeting in June this year. Although the proposed changes will not take effect, the topic is likely to be brought up again in the next revision cycle. Controversy over the difficulty of supervising the operation of multiple fire pump units in emergency situations, facilitating proper test functions, and ensuring the reliability of the overall system will continue. In addition, it is worth noting that although NFPA 20 will continue to allow vertical segmentation of fire pump units, certain jurisdictions do not allow this arrangement.
If a fire pump test header is installed, NFPA 20 requires it to be installed on an external wall or other location outside the pump room to allow drainage during the test. Outdoor layout is conducive to draining the water flow to a safe location, and minimize the impact of accidental drainage on fire pumps, controllers, motors, diesel engines, etc. A new attachment text has been added to address the conditions under which test heads can be considered for locations within the building. In the case that damage caused by theft or vandalism needs to be considered, the test header hose valve may be located in the building but outside the fire pump room. If according to the judgment of AHJ, the test flow can be safely directed outside the building without the need Improper risk of water spraying on fire pump equipment.
NFPA 20 has allowed flow meters to be used as water flow testing equipment for some time. At the time of installation, NFPA 25, the standard for inspection, testing and maintenance of water-based fire protection systems, requires flow meters to be tested and recalibrated every three years. However, NFPA 20 does not contain provisions to facilitate flowmeter calibration or recalibration. The 2013 version now requires that if the metering device is installed in a ring arrangement for fire pump flow testing, an alternative method of measuring flow is also required. The backup device should be located downstream of the flowmeter and connected in series with the flowmeter, and function within the flow range required for the full flow test of the fire pump. In addition, the standard will now state that an acceptable alternative to measuring flow is an appropriately sized test header. Unless the arrangement described in the above new regulations is provided, calibration of the flowmeter requires physical removal of the equipment and testing in an arrangement that may not reflect the actual pump and piping installation. In the long run, this approach can be cumbersome and expensive. In addition, changes in the piping arrangement and test arrangement may not match the actual pump installation, and the results of the recalibration may be questioned.
The previous version of NFPA 20 required the installation of the listed indicating butterfly valve or gate valve and drain valve or ball drop to the test head in the pipeline when the test header is located outside the pump or at a certain distance from the pump and there is a danger of freezing. The regulations have been revised to require butterfly valves or gate valves and drain valves or ball drops in all cases. If there is no valve, the water will reach the position of the test header under pressure, which is worrying. Water can be easily drained from the fire fighting system through the test header for non-fire fighting purposes. Another issue is the safety of the personnel conducting the pump test. The connection between the hose and the test header is safer, and there is no water pressure at the test header. After the test is completed, the spherical drip valve releases the pressure and water in the pipeline.
NFPA 20 currently stipulates that if a backflow preventer connected to the pump is required, special consideration should be given to the increase in pressure loss caused by the installation of the backflow preventer. Therefore, when the fire pump is operating at 150% of its rated capacity, NFPA 20 requires that a suction pressure of at least 0 psi be recorded for the installation. This requirement may be interpreted as meaning that the suction pressure is recorded at the return device instead of at the pump suction flange. The next version clarified the pressure reading at the suction port of the fire pump.
The requirements for earthquake protection have been clarified to indicate that they only apply to situations where local regulations specifically require the protection of fire protection systems from earthquake damage. In addition, the previous regulations regarding the installation of pump components have been deleted so that they can resist lateral movement equal to one-half of the weight of the equipment. NFPA 20 now requires horizontal seismic loads to be based on NFPA 13; SEI/ASCE7; or AHJ acceptable local, state, or international sources.
These changes are more consistent with current methods used to protect buildings and related mechanical systems from forces caused by seismic events. The concept of using half the weight of the equipment is not prudent in all situations. Users of NFPA 20 need to be aware that the horizontal loads generated will vary depending on the location of the project site. Although NFPA 13 provides a simplified method for determining load, and SEI/ASCE7 contains a more comprehensive method, NFPA 20 does not mandate the use of these reference standards, but allows AHJ to make the final decision.
NFPA 20 defines a packaged fire pump assembly as a fire pump unit assembly that is assembled in a packaging facility and delivered as a unit to the installation site. The components that need to be listed in the pre-assembled package include pumps, drives, controllers, and other accessories determined by the packager. These accessories are assembled on a base with or without a housing. The requirements for packaging components have been expanded. The pump unit components will be assembled and fixed on the steel frame structure. The welder who assembles the packaging unit shall meet the requirements of Section 9 of the ASME Boiler and Pressure Vessel Code or the American Welding Society AWS D1.1. The entire assembly must be listed for use by the fire pump, and designed and designed by the system designer in accordance with the instructions in NFPA 20. Finally, all plans and data sheets should be submitted to AHJ for review, and a stamped copy of the approved submission should be kept for record keeping.
These changes were made to better control who is responsible for ensuring that the complete pump unit is manufactured, installed, and operated as expected. Although the fire pump manufacturer is usually the entity that is required to solve any installation problems, the pump manufacturer is not necessarily the party that assembles the packaged fire pump components.
In some jurisdictions, direct connections between fire pumps and water sources, such as from a municipal water main, are not allowed. In other cases, municipal or other water sources cannot provide the maximum flow required by the fire protection system, or flow conditions fluctuate greatly. In both cases, the use of an interruption tank to interrupt or disconnect the connection to the water source provides a potential design choice. The interrupted water tank is a water tank that provides suction for the fire pump, but the capacity or size of the water tank is smaller than that required by the fire fighting system being served; that is, the water tank cannot contain the water required for the operation of the entire fire fighting system.
The cut-off tank is most commonly used (1) as a means to prevent backflow between the water supply source and the suction pipe of the fire pump, (2) eliminate the fluctuations in the pressure of the water supply source, (3) provide a stable and relatively constant suction pressure of the fire pump, and/ Or (4) Provide water storage to increase water sources that cannot provide the maximum flow required by the fire fighting system.
NFPA 20 requires that the size of the water tank be adjusted so that the water stored in the water tank with the automatic replenishment function must provide the maximum system demand flow and duration. With the fire pump running at 150% of its rated capacity, the size of the water tank must also last at least 15 minutes. In addition, NFPA 20 includes regulations regarding fuel tank refilling and requires that the refilling mechanism be listed and arranged for automatic operation. Specific filling regulations, such as those related to filling pipelines, bypass pipelines, liquid level signals, etc., are based on the overall size of the tank. If the size of the tank is such that its capacity is less than the maximum system requirement of 30 minutes, a set of regulations apply. If the tank is sized so that its capacity can meet the maximum system demand for at least 30 minutes, another set of regulations will apply. Revised and rearranged the paragraph on cut-off tanks to clarify applicable regulations based on tank size.
The NFPA provides additional guidance to facilitate pre-planned activities for the fire department to locate and provide fire pump equipment in high-rise buildings. As pointed out in the new annex text, the location of the pump room in a high-rise building requires due consideration. In the event of a fire, personnel are usually sent to the pump room to monitor or control the operation of the pump.
The most effective way to provide protection for these responders is to enter the pump room directly from the outside of the building. However, this arrangement is not always feasible or practical for high-rise buildings. In many cases, pump rooms in high-rise buildings need to be located on multiple floors above or below the ground.
When the pump room is not rated, NFPA 20 requires a protected passage between the stairs and the fire pump room. The fire resistance level of the passage must be the same as the fire resistance level required for the exit stairwell leading to the pump room. Many building and life safety regulations do not allow the pump room to lead directly to the enclosed exit staircase, because the pump room is not a space normally occupied. However, the passage between the stairwell leading to the pump room and the upper or lower pump room needs to be as short as possible and lead to other building areas as little as possible. This provides better protection for responders entering and leaving the pump room in the event of a fire.
The location and layout of the pump room should also ensure that the water discharged from the pump equipment (such as the packing gland) and the discharge valve and pressure relief valve are safely treated.
As part of Chapter 5, the concept of super high-rise buildings was introduced in the 2013 edition. A high-rise building is defined as a building on the habitable floor that is 75 feet above the lowest level of the fire department vehicle access. Previous NFPA 20 regulations have largely classified such buildings as the same category, regardless of whether the building is 200 feet or 2000 feet tall. However, some buildings are so tall that it is impossible for the pump equipment of the response fire department to overcome the associated height and friction losses to meet the flow and pressure requirements of the fire protection system on the highest floors. Although the previous version of NFPA 20 referred to structures or areas beyond the pumping capacity of fire department equipment in some cases, the 2013 version has more specific requirements for such “very tall buildings”. However, readers should be aware that some regulations for such situations are also located in Chapter 9, which deals with the power supply of electric fire pump installations.
For “very high buildings”, the fire pump installation needs to provide additional protection and redundancy, as described below. Instead of linking new regulations for very tall buildings to specific building heights, performance-based requirements related to responding to the pumping capacity of the fire department are proposed. The fire department purchases different equipment with different pumping capacity, so the standard based only on the maximum building height is quite limited. The design team now needs to specifically confirm the pumping capabilities of the fire department in response to each project. Additional regulations regarding redundant water tanks and fire pumps have also been added for very tall buildings.
If the main water supply source is a water tank, two or more water tanks are required. If each compartment can be used as a separate water tank, a single water tank that can be divided into two compartments is allowed. The total volume of all storage tanks or compartments must be sufficient to meet all the fire protection requirements of the relevant system. The size of each individual storage tank or compartment must ensure that at least 50% of the fire protection requirements can be stored when any one compartment or storage tank is out of service. Please note that this regulation does not require that each individual fuel tank or compartment can provide the requirements of the entire system. However, each fuel tank and/or fuel tank compartment must have an automatic filling device that can provide the complete system requirements. Although the provision of redundant storage tanks or compartments was introduced in the 2010 edition, it was officially used in super high-rise buildings in the 2013 edition.
Fire pumps in areas that partially or completely exceed the pumping capacity of fire department equipment must be equipped with a completely independent automatic standby fire pump unit or multiple units so that all areas can maintain full service when any pump is pumped out. Another option is to provide an auxiliary means to provide all fire protection requirements acceptable to AHJ. This second option allows negotiation with AHJ to provide redundant fire pump functions. A reasonably designed gravity feedwater riser system may be a choice to meet this requirement. Remember, there may be multiple AHJs for a particular design project.
The suction pipe supplying the fire pump needs to be flushed sufficiently to ensure that rocks, silt and other debris will not enter the pump or fire fighting system and cause damage. The previous version of the standard included two tables specifying the flushing speed of fixed pumps and positive displacement pumps. For the 2013 edition, these tables are merged, apply to all suction pipes, and are based on the nominal size of the suction pipe. The flushing rate of the smaller size pipes has also been revised to reflect a water flow rate of approximately 15 feet per second.
If the specified maximum flushing flow cannot be reached, the standard will allow the flushing flow to exceed 100% of the rated flow of the connected fire pump, or the maximum flow demand of the fire fighting system, whichever is greater. The new language indicates that this reduced flushing flow constitutes an acceptable test, provided that the flow exceeds the design flow of the fire protection system.
In addition, an attachment language was added to indicate that if the available water supply fails to meet the flow rate specified in the standard, a supplementary source, such as a pump from the fire department, may be needed. The standard will now also include language indicating that flushing procedures are to be performed, witnessed and signed before connecting to the fire pump.
Post time: Sep-16-2021
