1 Scope
NOTE This standard covers the design documentation requirements, materials, installation, testing, and acceptance criteria for automatic dry-pipe fire sprinkler systems. (1.1)
NOTE In a dry-pipe system the piping downstream of the dry-pipe valve is held under pressurized air or nitrogen rather than water. (1.2)
NOTE When one or more sprinklers open in response to heat, the supervisory gas escapes, the differential clapper in the dry-pipe valve trips, and water is admitted to the system and discharged through the open sprinklers. (1.3)
NOTE The scope extends from the supply-side connection at the dry-pipe valve assembly — including the trim, priming water connection (where used), air or nitrogen supply, accelerator or quick-opening device, intermediate chamber drain, and main drain — through all above-ground supply mains, cross mains, branch lines, and branch line end connections to the individual sprinklers. (1.4)
NOTE Auxiliary drains (drum drips) at low points, valve supervisory devices, the waterflow alarm pressure switch, the fire department connection, system pitch and drainage requirements, hanger and seismic bracing arrangements specific to dry-system pipe loading, and the system pressure-control air supply are included. (1.5)
1.6 Dry-pipe systems shall be the predominant choice wherever sprinkler piping cannot be maintained above 40°F (4°C), including unheated parking structures, exterior canopies, freezer warehouses, refrigerated rooms, mechanical penthouses, and other unconditioned spaces where a wet-pipe system would be vulnerable to freezing damage.
NOTE Water delivery time, not just hydraulic flow, is a defining constraint on a dry-pipe system, and the hydraulic design and the system volume govern all components together. (1.7)
1.8 Dry-pipe systems installed under this standard shall comply with NFPA 13, Standard for the Installation of Sprinkler Systems (current edition adopted by the Authority Having Jurisdiction), the International Fire Code (IFC), and the International Building Code (IBC) as adopted locally.
1.9 Where local amendments modify NFPA 13 requirements, the local amendment shall govern unless it is less stringent than the base standard, in which case the base standard governs.
1.10 The Contractor and the designer shall confirm the edition of NFPA 13 adopted in the jurisdiction prior to beginning design work.
NOTE Each successive edition of NFPA 13 has introduced meaningful changes to system volume limits, water delivery time, listed nitrogen-inerting allowances, pipe joining, and corrosion protection that affect both design and material procurement. (1.11)
1.12 This standard does not govern occupancy-specific or commodity-specific dry-pipe sprinkler systems designed under the storage chapters of NFPA 13 (rack storage in cold storage, frozen food warehouses, high-piled storage in unheated structures), which require specialized density, area, in-rack sprinkler, and water-delivery analysis beyond the scope of this document.
1.13 The Engineer of Record shall confirm whether storage-specific rules apply to any portion of the building before releasing this standard for use on a project.
NOTE Pre-action and deluge systems, although mechanically related to dry-pipe systems, are covered by separate SynC standards. (1.14)
2 Differentiation from Wet-Pipe Systems
NOTE Wet-pipe systems are mechanically simpler, deliver water immediately upon sprinkler opening, and have fewer maintenance points than dry-pipe systems. (2.1)
NOTE NFPA 13 Section 8.2 requires that wet-pipe systems be used wherever piping can be reliably maintained above 40°F (4°C). (2.2)
Unheated attic, concealed, or joist space
Parking garage or other unconditioned occupied space
Exterior canopy or walkway
Loading dock with overhead doors
Mechanical penthouse vented to exterior
Refrigerated cold storage room (35°F to 50°F)
Freezer warehouse (below 32°F)
Other — see basis of design
Per drawings
2.3 A dry-pipe system shall not be substituted for a wet-pipe system where a wet-pipe system is feasible.
2.4 Dry-pipe systems shall be selected only when freeze protection is required and when neither electric heat trace with insulation, antifreeze loops within the size limits permitted by NFPA 13, nor relocation of piping into conditioned space is practical.
2.5 The Engineer of Record shall document the rationale for selecting a dry-pipe system in lieu of a wet-pipe system in the basis-of-design narrative.
NOTE Common decision drivers that justify a dry-pipe selection are piping in attics, joist spaces, or concealed ceiling spaces in cold climates where intermittent heating is uncertain; freezer warehouse and refrigerated storage room protection; unheated parking decks above grade; exterior canopies and walkways; unconditioned loading dock areas with overhead doors that defeat space heating; and mechanical rooms vented to outside air. (2.6)
2.7 The decision to use a dry-pipe system shall not be made on construction cost alone.
2.8 The Owner shall be informed of the operational cost difference before the design is finalized, because a dry-pipe system has a meaningfully higher long-term inspection, testing, and maintenance burden than a wet-pipe system.
3 Referenced Standards
3.1 Materials, design, installation, and testing shall comply with the current adopted editions of the following standards.
| Standard |
Title |
| NFPA 13 |
Standard for the Installation of Sprinkler Systems |
| NFPA 20 |
Standard for the Installation of Stationary Pumps for Fire Protection |
| NFPA 24 |
Standard for the Installation of Private Fire Service Mains and Their Appurtenances |
| NFPA 25 |
Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems |
| NFPA 70 |
National Electrical Code |
| NFPA 72 |
National Fire Alarm and Signaling Code |
| NFPA 291 |
Recommended Practice for Fire Flow Testing and Marking of Hydrants |
| IBC |
International Building Code |
| IFC |
International Fire Code |
| ASTM A53 |
Standard Specification for Pipe, Steel, Black and Hot-Dipped, Zinc-Coated, Welded and Seamless |
| ASTM A135 |
Standard Specification for Electric-Resistance-Welded Steel Pipe |
| ASTM A234 |
Standard Specification for Piping Fittings of Wrought Carbon Steel and Alloy Steel for Moderate and High Temperature Service |
| ASTM A795 |
Standard Specification for Black and Hot-Dipped Zinc-Coated (Galvanized) Welded and Seamless Steel Pipe for Fire Protection Use |
| ASME B16.5 |
Pipe Flanges and Flanged Fittings |
| ASME B16.9 |
Factory-Made Wrought Buttwelding Fittings |
| ASME B16.11 |
Forged Fittings, Socket-Welding and Threaded |
| UL 199 |
Automatic Sprinklers for Fire Protection Service |
| UL 260 |
Dry Pipe Valves for Fire Protection Service |
| UL 262 |
Gate Valves for Fire Protection Service |
| UL 312 |
Check Valves for Fire Protection Service |
| UL 753 |
Alarm Accessories for Automatic Water-Supply Control Valves for Fire Protection Service |
| UL 1091 |
Butterfly Valves for Fire Protection Service |
| FM Global 2008 |
Approval Standard for Dry-Pipe Valves and Their Trim |
| FM Global 2011 |
Approval Standard for Accelerators for Dry-Pipe Valves |
| FM Global 2024 |
Approval Standard for Air Maintenance Devices for Sprinkler Systems |
| FM Global DS 2-0 |
Installation Guidelines for Automatic Sprinklers |
| FM Global DS 2-1 |
Corrosion in Automatic Sprinkler Systems |
| ANSI/AWWA C606 |
Grooved and Shouldered Joints |
3.2 Where standards conflict, the more stringent requirement shall govern unless directed otherwise by the Engineer of Record in writing.
4 Submittals
4.1 Action Submittals
4.1.1 The Contractor shall submit the following for the Engineer of Record's review and the Authority Having Jurisdiction's approval prior to procurement and installation.
NOTE The submittal package for a dry-pipe system is more demanding than for a wet-pipe system because the AHJ uses the package to verify both hydraulic compliance and the water delivery time requirement, which depends on the calculated system volume and the air supply arrangement. (4.1.2)
4.1.3 The following items shall be submitted as a coordinated package:
- Working drawings for the sprinkler system complying with NFPA 13 Chapter 28, including floor plans showing pipe routing, pipe sizes, sprinkler types, locations, and elevations; riser diagrams; hydraulic reference node diagram; pitch and drainage details with all auxiliary drain (drum drip) locations and elevations clearly indicated; and details of the dry-pipe valve assembly, air supply, and quick-opening device
- Hydraulic calculations performed by the pipe-sizing method, demonstrating that the system meets the design density and area requirements for each hazard area, with the water demand plotted against the water supply curve including all hose stream allowances and with the required safety margin demonstrated at the design point
- A calculated system volume (gallons or cubic feet) for the entire dry-pipe system, and where the volume exceeds the threshold for water delivery analysis, a water delivery time calculation demonstrating that water reaches the inspector's test connection in 60 seconds or less from the time the inspector's test valve is opened
- Product data for the dry-pipe valve, the accelerator or quick-opening device (where used), the air maintenance device or nitrogen generator, the air compressor (where used), all sprinklers including dry sprinkler barrel lengths and trim, valve supervisory switches, waterflow pressure switch, fire department connection, and hangers
- Manufacturer's installation instructions for the dry-pipe valve, accelerator, and nitrogen generator, including any limitations on application, system arrangement, or air-leakage tolerance that affect compliance
- A pipe pitch and drainage plan showing all low points, drum drip locations, main drain, and auxiliary drains, with elevation callouts that confirm compliance with the minimum pitch required by NFPA 13 (1/2 in. per 10 ft for branch lines and 1/4 in. per 10 ft for mains in steel-pipe systems)
- Seismic bracing calculations, where seismic bracing is required by the project's Seismic Design Category
☑ Working drawings per NFPA 13 Chapter 28
☐ Hydraulic calculations
☐ System volume calculation
☐ Water delivery time calculation
☐ Product data for all components
☐ Manufacturer installation instructions
☐ Pipe pitch and drainage plan with drum drip locations
☐ Seismic bracing calculations (if required)
4.1.4 No work shall proceed on any portion of the dry-pipe system until the corresponding submittals are reviewed, returned, and any required approval from the AHJ is in hand.
4.1.5 The Contractor shall submit the coordinated submittal package items listed above for the Engineer of Record's review and the AHJ's approval prior to procurement and installation.
4.1.6 Working drawings shall be prepared by or under the supervision of a person with qualifications acceptable to the AHJ.
NOTE The Contractor shall confirm designer qualification requirements before assigning the design work, because in many jurisdictions this means a licensed fire protection engineer or a NICET-certified designer at the level required by state law. (4.1.7)
4.2 Closeout Submittals
4.2.1 The following shall be submitted at substantial completion before the dry-pipe system is accepted:
- Contractor's Material and Test Certificate for Aboveground Piping (NFPA 13 Figure 29.1.1), signed by the installing contractor, certifying the pipe and fittings materials, joint types, flushing procedure, hydrostatic test results, air pressure test results, dry-pipe valve trip test results, water delivery time, alarm device operation, and inspector's test valve performance
- As-built drawings reflecting field changes from the reviewed working drawings, including any modifications to drum drip locations or pipe pitch
- Operation and maintenance manual including dry-pipe valve impairment procedures, air supply maintenance instructions, seasonal drain-down procedures for drum drips, NFPA 25 inspection intervals, and the manufacturer's reset procedure for the dry-pipe valve
- Warranty documentation for all components carrying a manufacturer warranty
- Hydraulic and water delivery design information signs confirming that installed signs match the design calculations
- Air leakage test record demonstrating compliance with the NFPA 13 air-leakage limit of 1.5 psi per 24 hours
☑ Contractor's Material and Test Certificate for Aboveground Piping
☐ Dry-pipe valve trip test record
☐ Water delivery time test record
☐ Air leakage test record (1.5 psi per 24 hours)
☐ As-built drawings
☐ Operation and maintenance manual
☐ Manufacturer warranty documentation
☐ Hydraulic and water delivery design information signs
4.2.2 The Contractor shall submit the closeout submittal items listed above at substantial completion before the dry-pipe system is accepted.
5 Quality Assurance
5.1 Installer Qualifications
NOTE Dry-pipe systems require specific design expertise beyond ordinary wet-pipe work. (5.1.1)
5.1.2 Dry-pipe sprinkler system installation shall be performed by a licensed fire protection contractor as required by the state and local jurisdiction.
5.1.3 In states where licensing is mandatory, the installing contractor shall hold a current fire protection contractor's license.
5.1.4 The individual preparing the working drawings and hydraulic calculations shall hold qualifications as required by the AHJ.
5.1.5 Where state law requires NICET certification, the designer shall hold NICET Level III or Level IV certification in water-based systems layout or fire protection engineering technology, as applicable.
5.1.6 The designer shall demonstrate prior experience with system volume sizing, water delivery time analysis, air supply selection, and quick-opening device integration.
5.1.7 Where the Contractor's in-house designer has limited dry-pipe experience, the design shall be subcontracted to a qualified fire protection engineering consultant or peer-reviewed by one.
5.1.8 The Contractor shall identify the design lead on the working drawings.
5.2 Coordination with Other Trades
5.2.1 The sprinkler Contractor shall coordinate early and continuously with the mechanical, electrical, structural, and architectural trades.
NOTE Dry-pipe systems impose additional coordination requirements beyond a wet-pipe system. (5.2.2)
5.2.3 The dry-pipe valve room or enclosure shall be in a heated space adjacent to the protected area.
5.2.4 The air compressor or nitrogen generator requires dedicated electrical service and possibly ventilation.
5.2.5 Auxiliary drains shall be accessible at every low point in the pipe network, including drains hidden above ceilings or in concealed combustible spaces.
NOTE The slope of the building structure may dictate pipe pitch direction and the resulting drum drip count. (5.2.6)
5.2.7 The location and structural capacity of the building structure to which hangers and seismic braces attach shall be confirmed with the structural engineer before hanger installation begins.
5.2.8 Hanger design loads shall account for the water-filled pipe weight plus an allowance for residual water that may remain after a trip, because dry-pipe pipe is filled with water during a hydrostatic test and during any post-trip discharge.
5.3 Listing and Approval
5.3.1 All sprinklers, dry-pipe valves, accelerators or quick-opening devices, air maintenance devices, nitrogen generators serving dry-pipe systems, valves, hangers, seismic brace assemblies, and alarm devices shall be listed by a Nationally Recognized Testing Laboratory (UL, FM, or another NRTL as accepted by the AHJ) for the specific application and service conditions.
5.3.2 Dry sprinklers shall be listed to UL 199 and shall be applied in accordance with their listing barrel length, orientation, and pendent or upright configuration.
5.3.3 The dry-pipe valve shall be listed to UL 260 and, where required by the Owner's insurance carrier, also approved to FM 2008.
5.3.4 Accelerators shall be listed and, where FM compliance is required, approved to FM 2011.
5.3.5 Air maintenance devices shall be listed and, where FM compliance is required, approved to FM 2024.
5.4 FM Global Compliance
5.4.1 Where the building's property insurance carrier or the Owner requires FM Global compliance, all components shall be FM-approved in addition to UL-listed.
● Not required
○ Required — FM-approved components throughout
5.4.2 Where the building's property insurance carrier or the Owner requires FM Global compliance, all components shall be FM-approved in addition to UL-listed.
NOTE A component that is UL-listed may not be FM-approved, and the difference is consequential for insurance purposes. (5.4.3)
5.4.4 The Contractor shall confirm FM approval status for each product at procurement, not after installation.
5.5 Corrosion Protection
NOTE Internal corrosion is a more aggressive problem in dry-pipe systems than in wet-pipe systems. (5.5.1)
NOTE The repeated wet-dry cycling of residual water trapped at low points, combined with the high oxygen content of air used as the supervisory gas, creates an environment in which microbiologically influenced corrosion (MIC) and oxygen-driven pitting can perforate the pipe wall in 10 to 20 years on systems that are not properly designed and maintained. (5.5.2)
NOTE NFPA 13 (2022 edition and later) recognizes nitrogen inerting as an alternative to galvanized pipe for corrosion control on dry-pipe systems. (5.5.3)
● Galvanized steel pipe throughout, air supervised
○ Black steel pipe, nitrogen inerted
○ Galvanized steel pipe, nitrogen inerted (enhanced protection)
○ Black steel pipe, air supervised (existing system replication only)
5.5.4 The Contractor shall provide one of three corrosion-mitigation approaches: galvanized steel pipe throughout the dry-pipe portion; nitrogen inerting of the dry-pipe system using a listed nitrogen generator that displaces oxygen; or both galvanized pipe and nitrogen inerting where the Owner's risk profile, insurance requirements, or service history warrants enhanced protection.
5.5.5 Where nitrogen is used, the system shall be evacuated of air and refilled with nitrogen to the listed purity level — typically 98 percent nitrogen or greater at the sprinkler.
5.5.6 Where nitrogen is used, the nitrogen generator shall be supplied with adequate compressed air capacity to maintain pressure during system leakage.
6 Environmental and Service Conditions
6.1 Temperature Range
NOTE Dry-pipe systems are designed to operate where the protected space drops below 40°F (4°C). (6.1.1)
4070
40506070
Default: 50 °F
6.1.2 The dry-pipe valve itself shall be installed in a heated enclosure or valve room maintained at not less than 40°F at all times.
6.1.3 The valve trim, priming water (where used), and supply-side piping shall not be allowed to freeze.
6.1.4 Where the protected space is a freezer, refrigerated room, or other deeply chilled environment, the designer shall account for the temperature differential at the valve-room-to-cold-space boundary and shall provide insulation, heat trace, or vapor barriers as required to prevent moisture migration into the dry-pipe piping during defrost cycles.
6.2 Maximum Working Pressure
NOTE The supply pressure to the dry-pipe valve also determines the required air pressure: a differential dry-pipe valve requires the air pressure to be maintained above a manufacturer-specified ratio of the water supply pressure (commonly 20 psi plus 25 percent of the maximum water supply pressure) to keep the clapper seated against false trips. (6.2.1)
40250
100125150175200250
Default: 150 psi
Per drawings
1560
15202530405060
Default: 40 psi
6.2.2 The system working pressure shall not exceed 175 psi at the dry-pipe valve unless the system is designed and the components are rated for a higher pressure.
6.2.3 Where the water supply static pressure exceeds 175 psi, a pressure-reducing valve shall be provided on the supply to the dry-pipe valve.
7 Design Basis and Hazard Classification
7.1 Occupancy Hazard Classification
NOTE Hazard classification is the single most consequential design decision for a sprinkler system because it directly determines the design density, the design area, and therefore the flow and pressure demand on the water supply. (7.1.1)
NOTE An incorrect hazard classification produces a system that is either inadequately protected (a life-safety deficiency) or grossly over-designed (an unnecessary capital cost). (7.1.2)
NOTE Light Hazard occupancies are characterized by low rates of heat release; in dry-pipe applications they include unheated office or institutional spaces, attic protection over light hazard occupancies, and exterior canopies over public assembly entrances. (7.1.3)
NOTE Ordinary Hazard Group 1 occupancies have moderate rates of heat release, with representative dry-pipe applications including unheated parking garages, mechanical penthouses, and loading docks. (7.1.4)
NOTE Ordinary Hazard Group 2 occupancies have higher rates of heat release, with representative dry-pipe applications including freezer warehouses (subject to NFPA 13 storage chapter cross-references), unheated repair garages, and certain industrial mezzanines. (7.1.5)
Light Hazard
Ordinary Hazard Group 1
Ordinary Hazard Group 2
Extra Hazard Group 1
Extra Hazard Group 2
Per drawings
7.1.6 The hazard classification shall be assigned by the designer based on the occupancy descriptions in NFPA 13 Chapter 5 and shall be confirmed with the Owner and the AHJ prior to finalizing the hydraulic design.
7.2 Design Density and Area
7.2.1 Design density and design area shall be determined from NFPA 13 Table 19.2.3.1.1 for the applicable hazard classification, with the dry-pipe adjustment applied.
NOTE For example, an Ordinary Hazard Group 1 dry-pipe system designed at 0.15 gpm/sq ft uses a design area of 1,950 sq ft rather than the 1,500 sq ft used for the equivalent wet-pipe system. (7.2.2)
0.10.6
0.10.150.20.30.40.450.6
Default: 0.15 gpm/sq ft
Per drawings
19506500
195026003250390052006500
Default: 1950 sq ft
Per drawings
7.2.3 NFPA 13 requires the design area for a dry-pipe system to be increased by 30 percent over the wet-pipe design area for the same hazard classification, in recognition of the delayed water delivery and the resulting larger fire size that may develop before water reaches the open sprinklers.
7.2.4 The 30 percent dry-pipe area increase is mandatory and shall not be reduced by the designer based on engineering judgment alone.
7.2.5 Where the system is equipped with a listed quick-opening device that meets the water delivery time requirement, the 30 percent area increase still applies; the quick-opening device shortens delivery time but does not eliminate the underlying delay.
7.3 Hose Stream Allowance
NOTE The hose stream allowance for a dry-pipe system is the same as for a wet-pipe system at the same hazard classification: 100 gpm for light hazard, 250 gpm for ordinary hazard, and 500 gpm for extra hazard. (7.3.1)
100 gpm (Light Hazard)
250 gpm (Ordinary Hazard)
500 gpm (Extra Hazard)
7.3.2 The hose stream demand shall be applied simultaneously with the sprinkler demand at the design area.
7.4 Water Supply Verification
Public water main — flow test required
Dedicated fire water storage tank and pump
Combined public main and storage tank
20150
405060708090100120150
Default: 70 psi
Per drawings
10130
20304050607080100130
Default: 50 psi
Per drawings
7.4.1 Water supply data shall be obtained by a hydrant flow test conducted at or near the project site in accordance with NFPA 291.
7.4.2 The flow test shall have been conducted no more than 12 months prior to the date of submittal.
7.4.3 Static pressure, residual pressure, and pitot flow shall be recorded.
7.4.4 The designer shall plot the water supply curve and confirm that the system demand including hose stream falls below the supply curve with the safety margin required by NFPA 13.
7.4.5 Where the available water supply does not meet the system demand, a fire pump shall be provided per Fire Pumps. 8 System Volume and Water Delivery Time
8.1 System Volume
NOTE System volume — the total internal volume of the dry-pipe piping downstream of the dry-pipe valve — is the dominant constraint on dry-pipe system design. (8.1.1)
NOTE A larger volume means more air to expel before water flows, which means slower water delivery. (8.1.2)
NOTE Systems above 750 gallons commonly require a listed accelerator or other quick-opening device, nitrogen inerting (which allows the listed gas-displacement curve to be used), and/or subdivision into multiple dry-pipe systems served by separate dry-pipe valves. (8.1.3)
501500
100250500750100012501500
Default: 500 gal
Per drawings
Volume below 750 gal — no mitigation required
Quick-opening device (accelerator) provided
Nitrogen inerting per NFPA 13
System subdivided into multiple dry-pipe valves
Combination — accelerator and subdivision
Combination — accelerator and nitrogen inerting
8.1.4 New dry-pipe systems shall not exceed 750 gallons (2,840 L) unless the designer demonstrates by calculation that water reaches the most remote inspector's test connection within 60 seconds of the test valve being opened.
8.1.5 The designer shall calculate system volume early in the design process — before pipe routing is finalized — so that any volume mitigations (subdivision, accelerator, nitrogen) can be incorporated into the layout.
NOTE Adding volume mitigations after the fact is significantly more expensive than designing for them from the beginning. (8.1.6)
8.2 Water Delivery Time
NOTE This is the defining performance criterion for a dry-pipe system. (8.2.1)
NOTE The water delivery time depends on system volume, pipe diameter and arrangement, air pressure, water supply pressure, and the presence or absence of a quick-opening device. (8.2.2)
1560
152030405060
Default: 60 seconds
8.2.3 Water shall reach the inspector's test connection at the hydraulically most remote point of the system within 60 seconds of opening the inspector's test valve, measured from the time the test valve is fully open.
8.2.4 For systems exceeding 750 gallons, the designer shall submit a water delivery time calculation using one of the accepted methods: the NFPA 13 spreadsheet-based volume/pressure method; a manufacturer's accelerator-specific delivery time calculation; or a computational fluid dynamics analysis where the geometry is too complex for tabular methods.
8.2.5 The AHJ may require a field water delivery test at acceptance to confirm the calculation.
9 Dry-Pipe Valve Assembly
9.1 Dry-Pipe Valve Type
NOTE The dry-pipe valve is the heart of the system. (9.1.1)
NOTE It is a listed differential-area valve in which the lower-pressure air on the clapper outlet acts on a larger area than the higher-pressure water on the clapper inlet, producing a force balance that keeps the clapper seated. (9.1.2)
NOTE When sprinkler operation releases the system air, the force balance collapses and the clapper opens to admit water. (9.1.3)
NOTE Differential dry-pipe valves are the historical standard and require an air-to-water pressure ratio of approximately 1:6 — that is, 25 psi of air will hold against 150 psi of water. (9.1.4)
NOTE Low-differential dry-pipe valves use a smaller differential area and require air pressure closer to the water pressure, but with the benefit of faster trip response. (9.1.5)
NOTE Low-differential valves are increasingly common because they pair well with nitrogen inerting (where nitrogen pressure is held closer to water pressure for a tighter operational margin). (9.1.6)
● Differential dry-pipe valve (standard ratio)
○ Low-differential dry-pipe valve
2 in.
2-1/2 in.
3 in.
4 in.
6 in.
8 in.
Per drawings
● Cast iron body, bronze trim
○ Ductile iron body, stainless steel trim
9.2 Valve Trim
9.2.1 The dry-pipe valve assembly shall be furnished with the manufacturer's standard listed trim, including a water-side pressure gauge and an air-side (or nitrogen-side) pressure gauge allowing the operator to confirm both pressures and clapper seating; an intermediate chamber drain that drains the small volume of priming water above the clapper to allow the valve to be reset after a trip; a main drain valve; an automatic ball drip on the supply piping between the dry-pipe valve and the fire department connection; a water-supply alarm pressure switch or waterflow alarm device that signals the fire alarm system when water enters the dry-pipe piping; and an air or nitrogen supply connection with a check valve, isolation valve, and pressure regulator as required by the air supply type.
9.2.2 The dry-pipe valve assembly shall be furnished with the manufacturer's standard listed trim.
9.2.3 The trim is not optional and shall not be field-assembled from non-listed parts.
9.2.4 The intermediate chamber shall be visibly observable through a sight glass or test cock so that the technician can confirm the chamber is dry before resetting.
9.2.5 The main drain valve shall be sized not smaller than 2 in. for draining the system after a trip or for periodic main drain testing.
9.2.6 The automatic ball drip shall drain any water that enters the FDC piping during cold weather without back-pressuring the dry-pipe valve.
9.3 System Control Valve
● OS&Y gate valve (interior riser)
○ Post-indicator valve (exterior / yard service)
○ Indicating butterfly valve with supervisory switch
9.3.1 The system supply to the dry-pipe valve shall be controlled by a listed indicating control valve installed upstream of the dry-pipe valve, in the same manner as a wet-pipe system.
9.3.2 The control valve shall be of the indicating type — OS&Y gate valve listed to UL 262, indicating butterfly valve listed to UL 1091, or post-indicator valve at exterior locations.
9.4 Valve Supervision
☑ Low air or nitrogen pressure supervisory switch
☐ High air or nitrogen pressure supervisory switch
☐ Valve room low-temperature supervisory switch (40°F)
☐ Main control valve tamper switch
9.4.1 The system control valve and any other valves controlling water to the dry-pipe system shall be supervised open by an electrically supervised tamper switch connected to the fire alarm system or an approved supervising station, in accordance with NFPA 72 and NFPA 13.
9.4.2 The dry-pipe valve assembly itself shall be equipped with a low-air-pressure supervisory switch that signals the fire alarm system when the air pressure falls below the listed minimum, indicating a system leak.
10 Quick-Opening Devices
10.1 Accelerators
NOTE The most common quick-opening device (QOD) is an accelerator, a listed device installed at the dry-pipe valve that detects the rate of air pressure drop in the system and rapidly equalizes the differential pressure across the clapper, tripping the valve sooner than it would have tripped on its own. (10.1.1)
● Not required — system volume below threshold and water delivery time met
○ Accelerator — listed for dry-pipe valve manufacturer
○ Nitrogen inerting in lieu of accelerator (NFPA 13 alternative)
○ Accelerator and nitrogen inerting (combined for largest systems)
10.1.2 A quick-opening device shall be provided where required by NFPA 13 — that is, where the calculated water delivery time without a QOD exceeds 60 seconds for a 750-gallon system, or where the Owner requires faster water delivery for property protection.
10.1.3 Accelerators shall be listed and, where FM compliance is required, approved to FM 2011.
10.1.4 The accelerator shall be installed strictly per the dry-pipe valve manufacturer's instructions.
10.1.5 Mixing accelerator and valve from different manufacturers is not permitted unless the combination is independently listed, because the accelerator and the dry-pipe valve are listed together as a system.
10.1.6 The accelerator shall include an anti-flood device to prevent water from entering the accelerator pilot line after the valve trips, which would otherwise damage the accelerator internals and produce a costly post-trip service event.
11 Air Supply
11.1 Air Compressor
NOTE Two compressor arrangements are recognized: a dedicated compressor that serves only the dry-pipe system through an air maintenance device, and a tank-mounted or plant compressor that serves multiple loads with the dry-pipe system connection regulated through an air maintenance device. (11.1.1)
NOTE The dedicated compressor arrangement is preferred for new construction because it isolates the dry-pipe system from plant air contamination and pressure fluctuations. (11.1.2)
● Dedicated air compressor — tank-mounted, single dry-pipe system
○ Dedicated air compressor — tankless, single dry-pipe system
○ Plant air through listed air maintenance device
○ Nitrogen generator — air compressor with N2 membrane or PSA module
1560
15304560
Default: 30 min
Manufacturer sizing per system volume
Per NFPA 13 Table A.16.7.4.1 (sizing tables)
Engineered sizing for combined-system loads
11.1.3 Where the supervisory gas is air, an air compressor shall be provided to maintain the system at the required air pressure.
11.1.4 The compressor shall be capable of restoring the system from atmospheric pressure to the required operating pressure within 30 minutes for systems up to 750 gallons, and within 60 minutes for larger systems, as permitted by NFPA 13.
11.1.5 The compressor shall be sized by the air maintenance device manufacturer's recommendation based on system volume, expected leakage rate, and required restoration time.
11.1.6 The air maintenance device shall be listed and, where FM compliance is required, approved to FM 2024.
11.1.7 The air maintenance device shall limit the rate of air introduction to the system so that a small leak does not mask a larger leak, because a system with oversized restoration capacity can fill faster than it can lose air through small leaks, allowing leaks to persist undetected until a major event reveals them.
11.2 Nitrogen Generator
NOTE A nitrogen generator consists of an air compressor, a moisture and oil filter train, and a nitrogen separation module (either a hollow-fiber membrane or a pressure-swing adsorption (PSA) module) that strips oxygen from compressed air to produce a nitrogen-enriched gas at the listed purity level. (11.2.1)
NOTE Nitrogen inerting eliminates the oxygen that drives internal corrosion in dry-pipe systems and is recognized by NFPA 13 as a corrosion-mitigation method. (11.2.2)
NOTE It is also recognized as a quick-opening alternative for system-volume purposes in some configurations, because the absence of oxygen alters the gas-discharge dynamics during a trip. (11.2.3)
NOTE Nitrogen generators are increasingly the default specification for new dry-pipe systems in cold-storage warehouses, healthcare facilities, and other long-life or critical assets. (11.2.4)
● Not applicable — air supervision
○ Membrane-type nitrogen generator
○ Pressure-swing adsorption (PSA) nitrogen generator
○ Continuous purge from generator to maintain purity
● Periodic timed purge at automatic vent
○ Initial purge only at commissioning
11.2.5 Where the supervisory gas is nitrogen, a listed nitrogen generator shall be provided.
11.2.6 The generator shall produce a gas of at least 98 percent nitrogen at the dry-pipe valve.
11.2.7 The system shall be purged of residual air during commissioning so that the nitrogen purity at the most remote sprinkler also reaches the listed level.
11.3 Air Leakage Limit
NOTE A leaky system masks itself with frequent compressor cycling that conceals the underlying defect; the air-leakage test is the only reliable way to verify joint integrity in an air-pressurized system. (11.3.1)
● 1.5 psi per 24 hours (NFPA 13)
11.3.2 NFPA 13 requires that the system not lose more than 1.5 psi of air or nitrogen pressure over 24 hours after the system is brought to operating pressure and isolated from the supply.
11.3.3 The Contractor shall conduct an air-leakage test at acceptance and shall document the result.
11.3.4 Leakage exceeding 1.5 psi per 24 hours indicates joint, fitting, or sprinkler thread defects that shall be located and corrected before the system is accepted.
12 Piping Materials
12.1 Steel Pipe
NOTE ASTM A795 is the purpose-written standard for fire protection piping and is the preferred specification because it was developed specifically for sprinkler service and includes both black and galvanized options. (12.1.1)
NOTE For dry-pipe systems the galvanized variant is strongly preferred over the black variant unless the system is also nitrogen-inerted, because internal corrosion in cycled wet-dry environments is significantly more aggressive than in continuously wet systems. (12.1.2)
● ASTM A795 (galvanized) — preferred for dry-pipe
○ ASTM A795 (black) — only with nitrogen inerting
○ ASTM A53 (galvanized)
○ ASTM A53 (black) — only with nitrogen inerting
○ Schedule 40 throughout
● Schedule 10 listed for dry-pipe service, 2 in. and larger; Schedule 40 for 1-1/2 in. and smaller
○ Schedule 10 listed for dry-pipe service throughout, grooved joints
12.1.3 Steel pipe shall conform to ASTM A795 or ASTM A53, as applicable.
12.1.4 Steel pipe used in dry-pipe systems shall be Schedule 40 for threaded joints in sizes 3 in. and smaller, and shall be Schedule 10 (listed for dry-system service) or Schedule 40 for grooved or welded joints.
12.1.5 The Contractor shall confirm that the specific pipe product carries the dry-system listing from the manufacturer, because not all Schedule 10 pipe is listed for dry-pipe service.
NOTE Thinner-wall pipe in a cycled wet-dry environment corrodes through the wall faster than thicker-wall pipe, which is why pipe manufacturers test and list specific products for the dry-pipe duty. (12.1.6)
12.1.7 The Contractor shall not thread Schedule 10 pipe, because threading Schedule 10 violates the pipe listing and is a common and serious field error.
12.1.8 CPVC pipe shall not be used in dry-pipe systems, because CPVC is listed only for wet-pipe service and the cycled drying and the impact of compressed air discharge during a trip exceed the CPVC pipe rating.
12.2 Fittings
☑ ASME B16.3 malleable iron threaded
☐ ASME B16.9 wrought buttwelding
☐ ASME B16.11 forged socket-welding or threaded
☐ ASME B16.5 flanges
☐ ANSI/AWWA C606 grooved couplings
☐ ASTM A234 wrought carbon steel
12.2.1 Steel fittings shall be listed for fire protection service and shall be compatible with the joining method and pipe schedule used.
12.2.2 Malleable iron threaded fittings shall be used with threaded Schedule 40 pipe.
12.2.3 Wrought carbon steel buttwelding fittings conforming to ASTM A234 and ASME B16.9 shall be used with welded joints.
12.2.4 Grooved mechanical couplings and fittings shall be listed and shall conform to ANSI/AWWA C606.
12.2.5 Forged fittings conforming to ASME B16.11 are permitted for socket-welding and threaded joints.
12.2.6 Flanges where used shall conform to ASME B16.5.
12.2.7 Galvanized fittings shall be used with galvanized pipe, because mixing black fittings with galvanized pipe defeats the corrosion protection at the threaded joint, which is the most corrosion-prone location in the system.
12.3 Joining Methods
Threaded (Schedule 40 only, 3 in. and smaller)
Grooved mechanical coupling (listed for dry-system service, 1 in. and larger)
Welded (Schedule 40, 1 in. and larger)
Grooved mains / threaded branch lines
12.3.1 Threaded joints shall use listed fire protection thread sealant applied to male threads only in accordance with the sealant manufacturer's instructions.
12.3.2 Polytetrafluoroethylene (PTFE) tape is not permitted as the sole thread sealant on fire protection threaded joints.
12.3.3 Threaded joints in dry-pipe systems shall be assembled with particular care because air-tightness — not just water-tightness — is required to meet the 1.5 psi per 24 hour leakage limit; minor thread imperfections that would seal water under pressure may leak air at the same pressure.
12.3.4 Grooved mechanical couplings shall be either rigid or flexible as required by NFPA 13 and the seismic design.
12.3.5 Coupling gasket compounds shall be compatible with the supervisory gas — standard EPDM gaskets are acceptable for air and nitrogen service.
12.3.6 Coupling installation torque shall be confirmed at every joint.
12.3.7 Welding shall be performed by welders qualified in accordance with AWS D10.12.
12.3.8 The weld joint shall be visually inspected for full penetration.
12.3.9 The weld area on galvanized pipe shall be repaired with cold-galvanizing compound after welding because the heat affected zone has lost its zinc coating.
13 Sprinklers
13.1 Sprinkler Types
NOTE A dry-pendent sprinkler is a specialized sprinkler with an extended barrel and an internal seal at the inlet, allowing the sprinkler to be installed pendent below a ceiling while keeping the supply piping above the ceiling in the heated space, and the barrel running through the unheated cavity. (13.1.1)
Upright (exposed piping)
Dry-pendent (heated supply, unheated cavity)
Dry-sidewall (heated supply, unheated room)
Per drawings
4 in.
6 in.
8 in.
10 in.
12 in.
18 in.
24 in.
Not applicable — upright only
Per drawings
13.1.2 All sprinklers shall be listed to UL 199 and shall be installed in accordance with their listing and the installation requirements of NFPA 13.
13.1.3 Sprinklers shall not be modified in any way, including bending of the deflector, painting, or application of any coating, after leaving the factory.
13.1.4 Factory-applied coatings provided by the manufacturer for corrosive environments are permitted; field-applied paint or coatings over sprinklers are prohibited.
13.1.5 Upright sprinklers shall be the default for exposed dry-pipe piping in mechanical rooms, parking garages, and warehouse spaces because their orientation prevents water from collecting in the sprinkler body and freezing.
13.1.6 Standard pendent sprinklers shall not be installed on dry-pipe systems because residual water at the sprinkler will freeze and damage the sprinkler.
13.1.7 Where pendent installation is required for architectural or coverage reasons, listed dry-pendent (or dry-sidewall) sprinklers shall be used.
13.1.8 The dry-pendent or dry-sidewall barrel length shall be sized so that the inlet seal sits in the warm side of the insulated separation; consult the manufacturer's barrel length tables.
13.2 Thermal Response
NOTE The NFPA 13 design density and area tables for dry-pipe systems are based on standard response sprinklers; mixing quick response sprinklers with a standard-response design produces unpredictable performance. (13.2.1)
● Standard Response (RTI > 80 (m·s)^0.5) — required for dry-pipe
○ Quick Response — only with engineered analysis and AHJ approval
NOTE Sprinklers are classified by thermal response as standard response or quick response based on the response time index (RTI) of the thermal element. (13.2.2)
13.2.3 Quick response sprinklers are not required in dry-pipe systems and shall not be used in dry-pipe systems unless specifically permitted by the listing and the hydraulic design accounts for the response timing.
13.3 Temperature Ratings
13.3.1 Counterintuitively, dry-pipe systems in cold spaces still require careful sprinkler temperature selection — a sprinkler in a freezer warehouse experiences extremely low ambient temperatures but may be located near a defrost heater, light fixture, or ceiling-mounted product that produces local heating well above the freezer setpoint.
Ordinary (135°F–170°F) — ambient up to 100°F
Intermediate (175°F–225°F) — ambient 101°F–150°F
High (250°F–300°F) — ambient 151°F–225°F
13.3.2 Sprinklers shall be selected for the temperature rating appropriate to the maximum expected ambient temperature at the ceiling level per NFPA 13 Table 8.3.2.1.
13.3.3 Ordinary temperature rating (135°F to 170°F) is appropriate for most dry-pipe applications, including freezer warehouses where ambient is below 32°F.
13.3.4 Intermediate temperature rating (175°F to 225°F) is required at locations near heat-emitting equipment in any space.
13.3.5 The Contractor shall verify temperature rating for sprinklers near unit heaters, radiant tubes, and ceiling-mounted defrost equipment.
13.4 K-Factor
NOTE The K-factor of a sprinkler determines the relationship between flow (Q in gpm) and pressure (P in psi) per the equation Q = K√P. (13.4.1)
NOTE Standard spray sprinklers are available in K-factors of 2.8, 4.2, 5.6, 8.0, 11.2, 14.0, and higher per NFPA 13. (13.4.2)
NOTE The K-5.6 sprinkler is the most widely used standard commercial sprinkler in dry-pipe applications. (13.4.3)
K-5.6 (17/32 in. orifice, standard commercial)
K-8.0 (large orifice)
K-11.2 (extra large orifice)
K-14.0
Per drawings — sprinkler schedule
13.4.4 Larger K-factors may be selected for dry-pipe applications where the design density and area combine to require a higher flow per sprinkler than K-5.6 can deliver at acceptable pressures.
13.5 Finish
Natural brass
Chrome
White paint (factory-applied)
Wax-coated (corrosive atmospheres)
Lead-coated (corrosive atmospheres)
Per drawings
13.5.1 Sprinkler finish shall be as scheduled for each area on the drawings.
13.6 Spare Sprinklers
6 sprinklers (≤300 heads installed)
12 sprinklers (301–1,000 heads installed)
24 sprinklers (>1,000 heads installed)
13.6.1 The Contractor shall provide a cabinet of spare sprinklers and one sprinkler wrench, mounted in the dry-pipe valve room or mechanical room, in accordance with NFPA 13.
13.6.2 The cabinet shall contain at minimum six sprinklers for systems with up to 300 sprinklers, 12 sprinklers for 300 to 1,000 sprinklers, or 24 sprinklers for systems with over 1,000 sprinklers.
13.6.3 Spare sprinklers shall represent each type, orifice size, temperature rating, and finish installed — including spare dry-pendent and dry-sidewall sprinklers where these are installed in the system.
14 Drainage
14.1 Pipe Pitch
NOTE The pitch is the primary mechanism by which residual water — from a hydrostatic test, a trip, condensation, or a partial trip-and-reset — is removed from the system. (14.1.1)
NOTE A dry-pipe system with sagging pipe or insufficient pitch will retain residual water at low spots, where the water freezes during the next cold cycle, ruptures the pipe, and floods the building when the rupture thaws. (14.1.2)
0.52
0.511.52
Default: 0.5 in per 10 ft
0.251
0.250.50.751
Default: 0.25 in per 10 ft
14.1.3 Dry-pipe system piping shall be pitched to drain back to the dry-pipe valve or to auxiliary drains (drum drips) at low points.
14.1.4 NFPA 13 requires minimum pitch of 1/2 in. per 10 ft for branch lines and 1/4 in. per 10 ft for mains in steel-pipe systems.
14.1.5 The Contractor shall verify pitch at every section of pipe during installation using a level.
NOTE Pitch deficiencies discovered after ceiling closure are extremely expensive to correct. (14.1.6)
14.2 Auxiliary Drains (Drum Drips)
NOTE A drum drip consists of a vertical short pipe with an isolation valve at the top and a drain valve at the bottom, separated by a small reservoir (the "drum") that collects accumulated water. (14.2.1)
NOTE To drain, the operator closes the upper valve, opens the lower valve to discharge collected water, closes the lower valve, and opens the upper valve again to restore system continuity. (14.2.2)
○ Single 1 in. drum drip at each trapped low point
● Two-valve drum drip assembly with isolation and drain valves
Per drawings — pitch and drainage plan
All drum drips in accessible mechanical space
Access panels provided at each drum drip
Some drum drips in plenums — coordinate ceiling access
Per drawings
14.2.3 Auxiliary drains, commonly called drum drips, shall be provided at every trapped section of pipe where water cannot drain back to the main drain by gravity.
14.2.4 Drum drips shall be located so that they can be reached for routine drainage.
14.2.5 The Contractor shall coordinate drum drip locations with the architect to provide access doors or accessible plenums at every drum drip.
14.2.6 Each drum drip shall be identified with a permanent sign indicating its location relative to the dry-pipe valve and the seasonal drainage schedule.
14.2.7 NFPA 25 requires drum drips to be drained as part of seasonal pre-winter maintenance — typically in the autumn before the first freeze — and after any system trip.
NOTE Missed drum drip drainage is the single most common cause of dry-pipe system freeze damage. (14.2.8)
14.3 Main Drain
Floor drain — interior heated valve room
Exterior discharge at grade
Discharge to storm system
14.3.1 A main drain valve of a size not smaller than 2 in. shall be provided at the dry-pipe valve assembly to allow the system to be drained completely for maintenance.
14.3.2 The main drain discharge shall terminate at a location where water can be discharged safely without causing property damage.
14.3.3 The main drain discharge shall include freeze protection where the discharge piping passes through unheated space.
15 Fire Department Connections
15.1 FDC Location and Accessibility
NOTE In most jurisdictions the AHJ will specify that the FDC be within 100 ft of a fire hydrant and clearly visible and accessible from the street or apparatus access road. (15.1.1)
15.1.2 A fire department connection (FDC) shall be provided for the dry-pipe sprinkler system in accordance with NFPA 13 and the International Fire Code.
15.1.3 The FDC shall be located on the exterior of the building at a point accessible to fire apparatus and approved by the Authority Having Jurisdiction.
15.1.4 The Contractor shall confirm the required FDC location with the AHJ prior to installation.
15.1.5 The FDC piping for a dry-pipe system shall include an automatic ball drip on the supply piping between the dry-pipe valve and the FDC to drain any water that enters the FDC piping during cold weather.
15.1.6 The FDC inlets and check valves shall be installed so that water from a fire department supply enters the system downstream of the dry-pipe valve clapper, bypassing the supervisory air.
15.1.7 The check valve at each FDC inlet shall prevent back-pressurization of the FDC piping and prevent loss of system air through the FDC during normal operation.
15.2 FDC Type and Size
● Siamese (two 2-1/2 in. inlets)
○ Single 4 in. LDH (large diameter hose) inlet
○ Siamese plus one 4 in. LDH inlet
● National Standard Thread (NST / NH)
○ Local fire department thread — confirm with AHJ
15.2.1 The FDC type, size, and inlet thread shall be as scheduled and shall be confirmed with the AHJ.
15.3 FDC Identification Signage
NOTE The "DRY" designation alerts the responding fire department to the delayed water delivery of a dry-pipe system, which affects how they will pressurize the FDC during operations. (15.3.1)
● "AUTO SPKR — DRY" per NFPA 13
○ "AUTO SPKR — DRY" plus zone identification
15.3.2 The FDC shall be identified with a sign reading "AUTO SPKR — DRY" in letters not smaller than 1 in. in height, in accordance with NFPA 13.
15.3.3 Where the building has multiple FDCs serving separate sprinkler systems (some wet, some dry), each FDC shall identify the zone and the system type.
16 Alarm and Supervisory Devices
16.1 Waterflow Alarm
NOTE The pressure switch is mounted on the alarm port of the dry-pipe valve and operates when water flows from the supply through the alarm port. (16.1.1)
NOTE Unlike a wet-pipe waterflow vane switch, the dry-pipe alarm pressure switch signals essentially instantaneously when the valve trips because water under full supply pressure reaches the alarm port within seconds of the clapper opening. (16.1.2)
16.1.3 Water motor gongs are particularly valuable for dry-pipe systems serving outbuildings or detached structures where the main fire alarm notification appliances may be remote.
☑ Electric alarm pressure switch connected to fire alarm system
☐ Water motor gong (exterior, hydraulic)
☐ Both — pressure switch and water motor gong
16.1.4 The dry-pipe valve shall be equipped with a listed waterflow alarm pressure switch that signals the fire alarm control panel when the valve trips, in accordance with NFPA 13 and NFPA 72.
16.1.5 A water motor gong may also be provided for local audible alarm without electrical power, in addition to the electric alarm pressure switch.
16.2 Low-Pressure Supervisory Switch
16.2.1 The low-pressure signal indicates a system leak that requires investigation; persistent low-pressure signals may also indicate an incipient trip and shall be treated as an urgent maintenance event.
☑ Low air or nitrogen pressure switch
☐ High air or nitrogen pressure switch
16.2.2 The dry-pipe valve shall be equipped with a listed low-pressure supervisory switch that signals the fire alarm control panel when the air or nitrogen pressure falls below the manufacturer's specified minimum (typically 5 to 10 psi below the normal operating pressure).
16.2.3 Some dry-pipe systems also include a high-pressure supervisory switch that signals when the air pressure exceeds the maximum acceptable value, indicating a malfunctioning air maintenance device or a pressure regulator failure that could mask an underlying leak or cause delayed valve operation.
16.3.1 A hydraulic design information sign shall be permanently affixed at the dry-pipe valve in accordance with NFPA 13, stating the design density, design area (with the 30 percent dry-pipe increase), required flow and pressure at the base of the riser, hose stream demand, total water demand, and K-factor.
16.3.2 Dry-pipe systems shall display a water delivery design information sign stating the calculated system volume, the calculated water delivery time, and the test result from the water delivery acceptance test.
17 Hangers and Seismic Bracing
17.1 Hanger Design and Spacing
C-clamp to steel flange
Beam clamp (side beam clip)
Through-bolt in concrete
Concrete insert (cast)
Power-driven fastener in concrete (listed)
Powder-actuated fastener in steel deck
Threaded rod from beam above
17.1.1 Hangers shall be listed for fire protection use and shall be installed in accordance with NFPA 13 Chapter 17 and the hanger manufacturer's listing.
17.1.2 Hangers shall be capable of supporting five times the weight of the water-filled pipe plus 250 lb at each point of support.
17.1.3 Hanger calculations for dry-pipe systems shall use the water-filled weight, not the air-filled weight, because the pipe is filled with water during hydrostatic testing and after every trip.
17.1.4 Steel pipe shall be supported at intervals not exceeding those specified in NFPA 13: 1-1/4 in. and smaller at 12 ft maximum spacing; 1-1/2 in. at 15 ft; 2 in. and larger at not more than 15 ft for standard hanger loads.
17.1.5 Hangers shall be located near each sprinkler and within 12 in. of every branch line end.
17.1.6 The Contractor shall not omit sprinkler-proximity hangers because of interference with other trades.
17.2 Seismic Bracing
NOTE Seismic design for dry-pipe systems follows the same provisions as for wet-pipe systems with one important addition: dry-pipe systems are more sensitive to joint failure during seismic events because the resulting loss of air pressure trips the valve and floods the system. (17.2.1)
● No — SDC A or B
○ Yes — SDC C
○ Yes — SDC D, E, or F (full bracing per NFPA 13 Chapter 18)
● Not required — SDC A or B
○ Required within 6 in. of each brace on 2-1/2 in. and larger pipe
○ Required — exact spacing per seismic calculations
17.2.2 Where the building is located in a Seismic Design Category (SDC) C, D, E, or F as defined by ASCE 7 and the IBC, lateral and longitudinal seismic bracing shall be provided for the sprinkler system in accordance with NFPA 13 Chapter 18.
17.2.3 Flexible couplings at the prescribed locations are essential.
18 Installation
18.1 Pipe Routing and Coordination
NOTE For dry-pipe systems, deviations from the reviewed working drawings are particularly consequential because pipe routing changes affect system volume, water delivery time, and the location and count of auxiliary drains. (18.1.1)
18.1.2 Working drawings approved by the AHJ govern the routing, sizing, and arrangement of all sprinkler piping.
18.1.3 Deviations from the reviewed working drawings require either a revised submittal or written approval from the Engineer of Record and the AHJ.
18.1.4 The Contractor shall not field-route dry-pipe piping without engineering review.
18.1.5 Sprinkler piping shall be routed to maintain the required minimum pitch.
18.1.6 Where structural elements, HVAC ducts, or other obstructions force the piping to deviate from a continuous fall, an auxiliary drain shall be provided at the resulting low point.
18.2 Cutting and Fabrication
18.2.1 Pipe shall be cut square and all burrs removed before jointing.
18.2.2 Threaded pipe shall be reamed after threading to remove the internal burr, because a cutting burr left inside the pipe impedes flow and accelerates corrosion.
18.2.3 Grooved pipe ends shall be roll-grooved or cut-grooved to the coupling manufacturer's dimension specifications.
18.3 Protection During Construction
NOTE Dry-pipe systems are particularly vulnerable to debris because the dry-pipe valve trim, accelerator, and air maintenance device contain small orifices that can be obstructed by particulates that pass through the dry-pipe valve during a trip. (18.3.1)
18.3.2 Dry-pipe piping shall be protected against contamination during construction.
18.3.3 All open pipe ends shall be capped when work is not in progress to prevent the introduction of debris, rodents, insects, and construction materials.
18.4 Field-Cut Pipe Coating
NOTE Failure to touch up field-cut galvanized pipe creates corrosion initiation sites at the threads, which is exactly the area most prone to trapped water and oxygen exposure. (18.4.1)
18.4.2 Galvanized pipe that is field-cut, threaded, or welded shall have the heat-affected or cut area touched up with a listed cold-galvanizing compound to restore the corrosion protection.
18.4.3 The Contractor shall include cold-galvanizing compound in the standard tool kit and shall apply it as a routine step during pipe installation.
19 Acceptance Testing
19.1 Flushing
19.1.1 The system piping shall be flushed before sprinklers are installed, in accordance with NFPA 13 and NFPA 24.
19.1.2 Flushing shall be performed at a flow velocity adequate to remove debris from the installation.
19.1.3 The flushing discharge shall be directed to an approved location and shall continue until the effluent runs clear.
19.1.4 The Contractor shall document the flushing by recording the date, the pipe sections flushed, the flow rate used, and the duration.
19.2 Hydrostatic Pressure Test
200400
200250300350400
Default: 200 psi
19.2.1 All piping shall be hydrostatically tested at 200 psi for 2 hours with no pressure loss at the test gauge and no visible leaks, in accordance with NFPA 13.
19.2.2 Where system working pressure exceeds 150 psi, the test pressure shall be the system working pressure plus 50 psi.
19.2.3 The hydrostatic test shall be conducted after all piping is complete, after flushing, and before ceilings are closed.
19.2.4 After the hydrostatic test is complete and witnessed, the system shall be thoroughly drained — including every auxiliary drain — before being placed in dry service.
19.2.5 The Contractor shall confirm that every drum drip is fully drained and operating before the system is placed in dry service.
19.3 Air Pressure Test
19.3.1 The air test detects joint leaks that may have sealed under water pressure but leak air; this is a non-trivial number of joints in any new system.
4060
405060
Default: 40 psi
19.3.2 In addition to the hydrostatic test, the system shall be air-tested at 40 psi for 24 hours with a pressure loss not exceeding 1.5 psi at the end of the test, in accordance with NFPA 13.
19.3.3 The air test shall be conducted after the system is drained from the hydrostatic test and before the system is placed in service.
19.3.4 Leaks shall be located by soap-bubble testing or ultrasonic leak detection and corrected before retest.
19.4 Dry-Pipe Valve Trip Test
NOTE The trip test confirms that the valve operates as listed and that the calculated water delivery time is achieved in practice. (19.4.1)
19.4.2 The dry-pipe valve shall be trip-tested by opening the inspector's test valve at the most remote point of the system and timing the interval until water discharges from the inspector's test connection.
19.4.3 Trip tests shall be performed both with the quick-opening device (where installed) in service and, where required by the AHJ, with the QOD bypassed.
19.4.4 The water delivery time at the trip test shall not exceed 60 seconds from opening of the inspector's test valve to water discharge, in accordance with NFPA 13.
19.4.5 The trip test result shall be recorded on the Contractor's Material and Test Certificate.
19.4.6 Where the field-measured delivery time exceeds the calculated value, the cause shall be investigated and corrected; common causes include partially obstructed orifices in the dry-pipe valve trim, insufficient pipe pitch causing air entrapment, or undersized air supply.
19.5 Alarm Device Test
19.5.1 The waterflow alarm pressure switch shall be tested as part of the trip test by confirming that the fire alarm control panel receives the alarm signal when the valve trips.
19.5.2 The valve supervisory switches for all supervised control valves shall be tested by partially closing each valve and confirming that the fire alarm control panel receives the supervisory signal within two turns of the handwheel.
19.5.3 The low-pressure supervisory switch shall be tested by bleeding air pressure from the system through the inspector's test valve and confirming the supervisory signal at the manufacturer's specified pressure.
19.6 Main Drain Test
20200
4050607080100120150175200
Default: 70 psi
Per drawings
10180
20304050607080100120150
Default: 50 psi
Per drawings
19.6.1 The main drain shall be fully opened with all supply valves open and the static pressure and residual flowing pressure shall be recorded.
19.6.2 The flowing pressure at the main drain shall be documented and compared to the design water supply data.
19.6.3 The main drain test result shall be recorded on the Contractor's Material and Test Certificate and shall serve as the baseline for future NFPA 25 annual main drain tests.
19.7 Contractor's Material and Test Certificate
19.7.1 The Contractor shall complete and sign a Contractor's Material and Test Certificate for Aboveground Piping using the form provided in NFPA 13 Figure 29.1.1 or an equivalent form approved by the AHJ.
19.7.2 The certificate for a dry-pipe system shall document the same items as a wet-pipe system plus the dry-pipe valve trip test result with water delivery time; the air pressure test result with measured pressure loss over 24 hours; the air supply type and capacity; the quick-opening device (where installed) and its tested operation; and the verification of all auxiliary drain functionality.
19.7.3 The certificate shall be executed at the time of acceptance and retained permanently with the Owner's facility documentation.
19.8 Acceptance Inspection by AHJ
NOTE The AHJ's acceptance inspection for a dry-pipe system commonly includes witnessing the trip test and water delivery time measurement, verifying sprinkler placement, confirming hanger spacing and pipe pitch, testing alarm and supervisory devices, and reviewing the Contractor's Material and Test Certificate. (19.8.1)
19.8.2 The Contractor shall schedule an acceptance inspection with the Authority Having Jurisdiction after the system is complete, tested, and all deficiencies from preliminary inspections are corrected.
19.8.3 The system shall not be placed in service — and no certificate of occupancy shall be issued — until the AHJ has conducted the acceptance inspection and issued approval.
20 Ongoing Inspection, Testing, and Maintenance
NOTE NFPA 25 establishes mandatory intervals for inspecting system components, testing alarm devices, conducting main drain tests, performing the dry-pipe valve trip test, and servicing the air supply. (20.1)
● Service agreement with qualified fire protection contractor
○ Owner-performed per NFPA 25 (qualified personnel required for testing)
20.2 The dry-pipe system shall be inspected, tested, and maintained throughout the life of the building in accordance with NFPA 25, current adopted edition.
20.3 Specific NFPA 25 requirements for dry-pipe systems shall include weekly or monthly inspection of the air or nitrogen pressure gauge and the dry-pipe valve enclosure heating; quarterly testing of waterflow and supervisory alarm devices; quarterly testing of low-pressure supervisory; annual full-flow trip test of the dry-pipe valve with the quick-opening device in service (and a separate test with the QOD bypassed in some jurisdictions); seasonal draining of every auxiliary drain (drum drip) before the first freeze and after every trip; 3-year internal inspection of the dry-pipe valve; and 5-year internal pipe assessment to check for obstruction, corrosion, and microbiological growth.
20.4 Dry-pipe systems shall be drained, dried, and refilled with fresh supervisory gas as part of the 3-year internal inspection.
20.5 The Owner shall maintain a service agreement with a qualified fire protection service contractor to perform NFPA 25 inspections and tests at the required intervals.
20.6 Owner-performed inspections are permitted for certain visual tasks, but trip tests, internal valve inspections, and 5-year internal pipe assessments shall be performed by qualified service personnel.
20.7 Records of all inspections, tests, and maintenance activities shall be retained on-site and made available to the AHJ upon request.
21 Warranty
1 year from substantial completion
2 years from substantial completion
● 4 hours maximum for restoration or alternative protection
○ As required by AHJ impairment plan
21.1 The Contractor shall warrant all materials and workmanship against defects for the project warranty period.
21.2 The warranty shall cover the complete installed system including pipe, fittings, hangers, seismic bracing, the dry-pipe valve, quick-opening device, air supply (compressor or nitrogen generator), alarm and supervisory devices, fire department connection, and all specialties.
21.3 Sprinklers carry individual manufacturer's limited warranties as stated in the manufacturer's product data; the Contractor shall pass through these warranties to the Owner.
21.4 The warranty period shall run from the date of substantial completion.
21.5 The Contractor shall correct, at no cost to the Owner, any leaks, failures, or deficiencies that arise from defective materials or workmanship during the warranty period.
21.6 Warranty service for dry-pipe systems shall include investigation of any persistent low-air-pressure alarms — a sign of joint leakage that may not have been present at acceptance but emerges as gaskets and joints age through the first heating and cooling cycles.
21.7 Any system impairment shall be handled in accordance with NFPA 25 impairment procedures, including prompt notification to the Owner, the monitoring station, the fire department, and the insurance carrier.
NOTE Returning an impaired dry-pipe system to service requires re-pressurization, drainage of any test water, and reset of the dry-pipe valve including verification of the intermediate chamber drain. (21.8)
21.9 The Contractor shall maintain the ability to restore impaired systems to full service within the time limits required by the AHJ and the Owner's insurance carrier.