NFPA 13: System Components — Pipe, Fittings and Valves

The reliability of a sprinkler system is decided by the parts that site crews handle most: pipe, fittings and valves. The system components part of NFPA 13 sets which standards these items must meet, which joining method may be used where, and how valves are supervised. This article is part of the NFPA 13 Clause Guide series and summarises those rules from the design office and site perspective.

Pipe: material and wall thickness

Carbon steel is the most common material for above-ground sprinkler pipe. The standard requires steel pipe to comply with recognised product standards such as ASTM A53, A135 and A795. Copper tube and, under defined conditions, listed CPVC pipe may also be used. Stainless steel and special alloy pipe are accepted as listed products.

Wall thickness is tied directly to the joining method:

To compare materials on corrosion, cost and installation speed, see our sprinkler pipe material comparison.

CPVC and plastic pipe

CPVC may be used within its listing, typically in light hazard and residential occupancies. It has two critical weaknesses: chemical incompatibility and limits on exposed installation. Certain oils, cutting fluids, firestop sealants and cable jackets are incompatible with CPVC and cause environmental stress cracking. Do not use any material near it without checking the manufacturer's compatibility list. Exposed installation is restricted to the ceiling and sprinkler types the listing allows.

Fittings and joining

• Fittings must comply with the relevant product standard or be listed, and be rated for system pressure.
• Bushings are restricted. The general rule is to change size with a one-piece reducing fitting; bushings are allowed only in the limited cases the standard describes.
• Gaskets in grooved couplings must suit the system type; dry and pre-action systems need gaskets that seal at low temperature.
• Flexible sprinkler hose is listed; use the listed length, bend radius and equivalent pipe length in the hydraulic calculation.
• Hole-cut outlets (mechanical tees, saddles) must be listed, and the coupon cut from the pipe must be retrieved. A coupon left inside can block sprinklers downstream.

Valves and supervision

Valves controlling the water supply must be listed indicating valves: OS&Y gate valves, butterfly valves with an indicator, or post indicator valves (PIVs). It must be possible to see from a distance whether the valve is open or shut. These valves must also not close in less than 5 seconds when operated at maximum speed from fully open, to limit water hammer.

Control valves must be supervised in the open position. Accepted methods:

1. Electrical supervision (tamper switch) connected to the fire alarm panel.
2. A local alarm reporting to a monitored location.
3. Locking in the open position.
4. Sealing, only under certain conditions and with regular inspection.

Other hardware

• Check valves: needed where more than one supply is connected and at the fire department connection.
• Test and drain: every system needs a main drain, an inspector's test connection at the remote end and, on dry systems, low-point drains.
• Pressure gauges: on both the supply and system sides of the alarm valve.
• Hangers: listed hangers at the maximum spacing given in the standard, which varies with pipe size and material.
• Seismic protection: flexibility, lateral and longitudinal bracing in seismic regions; see seismic bracing for sprinklers.

Pressure rating

All components must be rated for at least 12.1 bar (175 psi) working pressure. On pumped systems, if churn plus suction pressure exceeds this, select higher-rated valves, fittings and sprinklers or zone the system.

How components affect the hydraulic calculation

Pipe material and system type set the Hazen-Williams C-factor. Black or galvanised steel uses 120 for wet systems and 100 for dry and pre-action systems; copper, stainless steel and plastic pipe use 150. A lower C on a dry system means higher friction loss for the same pipe size, so pipe sizes must be rechecked when part of a wet system is converted to dry. Fittings and valves are included as equivalent pipe lengths; for listed products (flexible hose, butterfly valves, grooved fittings) use the manufacturer's equivalent length.

Common mistakes

• Threading thin-wall pipe.
• Using firestop sealant or cutting oil that is incompatible with CPVC.
• Leaving the coupon inside the pipe at hole-cut outlets.
• Tamper switches fitted but never wired to the panel.
• Bushings used freely at size changes.
• Couplings on a dry system fitted with wet-system gaskets.

Material submittal checklist

• Does the pipe product standard and wall thickness suit the joining method?
• Are fittings, couplings and flexible hoses listed, and are the listing conditions met?
• Are control valves of the indicating type and supervised?
• Does the component pressure rating cover the maximum system pressure?
• If CPVC is used, is the compatibility list available on site?

Frequently Asked Questions

Which C-factor is used for dry systems?

For black and galvanised steel, 100 for dry and pre-action systems and 120 for wet systems. Copper, stainless steel and plastic pipe use 150.

Can Schedule 10 pipe be threaded?

Generally no. Threaded joints need at least Schedule 40 below 8 in. Thin-wall pipe is joined with grooved couplings or welding; specially listed thin-wall pipe suitable for threading is the exception.

How quickly may a control valve close?

Indicating control valves must not close in less than 5 seconds when operated at maximum speed from fully open, to limit water hammer.

Is sealing enough for valve supervision?

Sealing is one accepted method, but usually only under certain conditions and with regular inspection. Electrical supervision with a tamper switch is the most reliable method.

Can CPVC pipe be used anywhere?

No. CPVC may only be used within the hazard classes and installation conditions of its listing, and must not contact incompatible chemicals.

SprinkCalc — Fire Sprinkler Design Across Three Standards

SprinkCalc covers hazard classification, design density and area, K-factor selection, water demand and hydraulic calculations for NFPA 13, FM Global and BS EN 12845 in a single iOS app, and exports a professional PDF report.

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