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SYSTEM COMPONENTSNFPA 13NFPA 25

Alarm Check Valve
The Heart of the Wet Riser

Installed at the base of every wet sprinkler riser, the alarm check valve permits water to flow toward sprinklers while triggering the alarms that alert occupants and first responders.

By Stanislav Samek, Samektra · 9 min read · Last updated April 17, 2026
Complete alarm check valve assembly — flanged valve body with retard chamber, water motor gong, pressure gauges, alarm test valve, and main drain ball valve. UL Listed, FM Approved.
A Viking alarm check valve installed in a facility riser room — flanged top, trim line running off the alarm port, Summit pressure gauge, and main drain cup below for the routine drain test.

Exploded View: Tyco AV-1-300 Alarm Check Valve

The Tyco AV-1-300 is one of the most common alarm check valves in North American wet sprinkler systems. Rated 300 psi / 20.7 bar in sizes 2½", 4", 6", and 8" (groove × groove, flange × groove, or flange × flange end connections), it uses a divided-seat ring and rubber-faced clapper to route a trickle of flow into the alarm port whenever the clapper lifts off its seat. The exploded drawing below is the authoritative field reference for the 5-year internal inspection and for ordering replacement parts.

Component callouts (from Figure 1)

1Valve Body — Ductile-iron — NR (not replaceable)
2Handhole Cover — Bolted access for internal inspection
3Handhole Cover Gasket — Replace every time the cover opens
4Seat Ring — Divided seat — half routes flow to alarm port
5Clapper — Rubber-faced, hinged
6Clapper Facing — Rubber wear surface — first to erode
7Clapper Washer — Retains the facing
8Lock Nut / Self-Locking Hex Cap Screw — Holds facing to clapper
9Clapper Hinge Pin — Stainless — check for play at 5-year internal
10Clapper Hinge Pin Bushing — Wears before the pin does
11Clapper Spring — Provides positive seating; measure free length
12Hex Bolts — 4 or 6 bolts depending on valve size
13Square Head Pipe Plug — 3/4" NPT — on 4", 6", 8" valves only

Replacement part numbers (from Tyco parts sheet)

  • 2½" Valve — Repair Kit 92-200-1-216 · Clapper Assembly 92-200-1-218
  • 4" Valve — Repair Kit 92-200-1-416 · Clapper Assembly 92-200-1-423
  • 6" Valve — Repair Kit 92-200-1-620 · Clapper Assembly 92-200-1-623
  • 8" Valve — Repair Kit 92-200-1-816 · Clapper Assembly 92-200-1-823

F × F (flange × flange) valve shown for reference; components for G × G (groove) and F × G (flange × groove) valves are shared.

What Is an Alarm Check Valve?

An alarm check valve is a specialized check valve equipped with an alarm port, installed at the base riser of a wet sprinkler system. It serves two simultaneous functions: it allows water to flow in one direction only — from the supply toward the sprinklers — and it triggers an audible and/or electrical alarm when sustained water flow occurs NFPA 13, §8.16.

Defined in NFPA 13 and listed under UL 193, the alarm check valve is the dividing line between the water supply and the sprinkler system. Every wet sprinkler riser requires one. When a sprinkler head opens and water begins to flow, the alarm check valve clapper lifts, water enters the alarm port, and the building is notified through a water motor gong on the exterior and/or an electric pressure switch connected to the fire alarm control panel.

Without a properly functioning alarm check valve, a wet sprinkler system can still suppress a fire — but no one will know it is happening until they see the water.

How the Alarm Check Valve Works

The alarm check valve contains a hinged clapper (disc) seated against a machined seat inside the valve body. Under normal standby conditions, static water pressure holds the clapper closed. The pressure is equalized on both sides of the clapper, keeping the valve sealed and the alarm port dry NFPA 13, §8.16.1.

Activation Sequence
1A sprinkler head activates due to heat — system pressure drops on the downstream side of the clapper
2Supply-side water pressure lifts the hinged clapper off its seat
3Water flows through the valve body toward the open sprinkler head
4Water simultaneously enters the alarm port in the valve body
5Alarm port water passes through the retard chamber, which absorbs brief pressure surges to prevent false alarms
6If flow is sustained, water continues past the retard chamber to the water motor gong (mechanical alarm) and/or pressure switch (electric alarm)
7The water motor gong sounds on the building exterior; the pressure switch sends an alarm signal to the FACP

Key Components

Every alarm check valve assembly includes several critical components that work together to provide reliable one-way flow and alarm signaling.

Main Valve Body

Cast iron or ductile iron housing with flanged or grooved connections. Contains the clapper seat and alarm port. Sizes range from 3" to 8" to match the riser pipe.

Clapper (Hinged Disc)

The moving check element — a rubber-faced disc on a hinge pin. When water flows, it swings open. When flow stops, gravity and back-pressure reseat it against the machined seat.

Alarm Port & Trim

A small-bore port on the valve body connected to external piping (the "alarm trim") that routes water to the retard chamber, water motor gong, and/or pressure switch.

Retard Chamber

A small tank in the alarm trim line that collects water from brief pressure surges. A drain orifice at the bottom allows surge water to drain before it can trigger the alarm, preventing false activations.

Alarm Test Valve (Bypass)

A manually operated valve in the alarm trim that bypasses the retard chamber. Opening it sends water directly to the alarm devices for quarterly testing without requiring a sprinkler head to activate.

Main Drain Connection

A valved connection on the system side used for the main drain test. Flowing water through the main drain verifies supply adequacy and valve operation.

Pressure Gauges

Two gauges — one on the supply (inlet) side and one on the system (outlet) side. Comparing readings helps identify clapper leaks, supply problems, or closed valves.

Trim Shut-Off Valves

Isolation valves in the alarm trim piping that allow maintenance on the retard chamber, gong, or pressure switch without draining the system. Must remain open during normal service.

Types and Configurations

Flanged

Traditional connection with bolt-pattern flanges on the inlet and outlet. Common in older installations and larger pipe sizes (6" and 8"). Requires gaskets and bolt torque to spec.

Grooved

Modern grooved-end connections using mechanical couplings (e.g., Victaulic). Faster installation, easier maintenance access, and reduced seismic vulnerability. Now the standard for most new construction.

Common sizes are 3", 4", 6", and 8", matched to the riser pipe diameter. Major manufacturers include Viking, Tyco/Johnson Controls (now part of Johnson Controls), Reliable Automatic Sprinkler, and Globe Fire Sprinkler. All alarm check valves installed in fire protection service must be UL 193 listed and approved by the AHJ.

NFPA 13 Installation Requirements

NFPA 13 specifies where and how alarm check valves must be installed to ensure reliable performance NFPA 13, §8.16.

  • Heated location: The alarm check valve and all trim piping must be in a space maintained at or above 40 degrees F to prevent freezing
  • Accessible: Must be readily accessible for inspection, testing, and maintenance — not concealed behind walls or above inaccessible ceilings
  • Alarm trim: Piped to a water motor gong on the building exterior and/or to a pressure switch connected to the FACP
  • Retard chamber: Sized per the manufacturer's listing — prevents false alarms from water hammer and pressure surges
  • Identification sign: A permanent sign at the valve must identify the system it serves, the number of sprinklers, and the building area covered
  • Vertical orientation: Installed in the vertical riser with flow direction arrow pointing up, unless the manufacturer provides specific approval for other orientations
  • Alarm test valve: A bypass valve must be installed to allow quarterly alarm testing without activating a sprinkler head

NFPA 25: Alarm Check Valve ITM Schedule

NFPA 25, Chapter 13, establishes the inspection, testing, and maintenance requirements for alarm check valves. These are among the most commonly tested items during a wet sprinkler system inspection NFPA 25, Ch. 13.

FrequencyRequirementReference
MonthlyExternal inspection — verify valve is accessible, no visible leaks, gauges readable and in good condition, trim valves openNFPA 25, §13.1.1
QuarterlyAlarm test — open the alarm test valve and verify the water motor gong sounds and/or the electric alarm activates at the FACP within 90 secondsNFPA 25, §13.2.5
QuarterlyMain drain test — open the main drain fully to verify adequate water supply; record static and residual pressuresNFPA 25, §13.2.5
AnnuallyExterior inspection of all valve components — check for corrosion, mechanical damage, proper signage, and correct valve positionNFPA 25, §13.1.1
5 YearsInternal inspection — open the valve, inspect the clapper, seat, hinge pin, and interior for corrosion, scale, debris, or biological growthNFPA 25, §13.4.2
5 YearsClean strainers, filters, and restricted orifices in the alarm trim piping — remove mineral deposits and debrisNFPA 25, §13.4.2

Common Deficiencies

These are the issues inspectors and service technicians encounter most frequently with alarm check valves in the field.

Trim Valves Shut Off

The most critical deficiency. Someone closes the trim shut-off valves — often to silence a false alarm — and forgets to reopen them. The sprinkler system still works, but no alarm will ever sound. This defeats the entire purpose of the alarm check valve.

Retard Chamber Not Draining

The drain orifice at the bottom of the retard chamber becomes clogged with sediment or mineral deposits. Water accumulates and eventually reaches the alarm devices, causing nuisance alarms from minor pressure fluctuations.

Internal Corrosion on Clapper/Seat

Over time, the clapper face and seat corrode or develop scale, preventing a tight seal. This allows water to weep past the clapper into the alarm port during normal standby, causing intermittent false alarms.

Missing or Broken Alarm Test Valve

The bypass valve used for quarterly testing is missing, seized shut, or has a broken handle. Without it, quarterly alarm testing requires alternative methods or cannot be performed, resulting in a deficiency.

Gauges Not Readable

Supply-side and system-side pressure gauges are broken, fogged, or have needles stuck. Gauges are essential for evaluating valve condition and water supply — unreadable gauges are cited on every inspection.

Valve Inaccessible

Storage, equipment, or construction blocks access to the alarm check valve. If the inspector cannot reach it, neither can the fire department or the service technician during an emergency.

Related System Components

The alarm check valve is a central component in the wet sprinkler system, connecting the water supply to the alarm signaling chain.

Wet Sprinkler SystemThe system type where alarm check valves are required — the valve sits at the base of every wet riser→Water Motor GongMechanical alarm device driven by water from the alarm port — provides exterior audible notification without electricity→Waterflow SwitchElectronic flow detection device — often used in conjunction with or as an alternative to the alarm check valve pressure switch→Control ValveThe OS&Y or PIV valve upstream of the alarm check valve that isolates the sprinkler system for maintenance→Inspector's TestTest station at the remote end of the system — used to verify waterflow alarms by simulating sprinkler activation→NFPA 25 ReferenceComprehensive ITM standard governing inspection, testing, and maintenance of all water-based fire protection system components→

▶ Watch: Alarm Check Valve — How It Works

Frequently Asked Questions

What is an alarm check valve?
An alarm check valve is a specialized swing check valve at the base of every wet sprinkler riser. It enforces one-way water flow (supply → system) AND signals an alarm whenever sustained flow occurs. A divided-seat ring routes a trickle of water into an alarm port connected to a retard chamber and then to a water-motor gong (exterior mechanical alarm) and/or an electric pressure switch tied to the FACP. UL 193 is the listing standard.
What is the difference between a check valve and an alarm check valve?
A standard check valve only blocks reverse flow. An alarm check valve does the same PLUS it sounds an alarm the moment water starts moving through the riser. The functional difference is the divided-seat ring and alarm port; the mechanical difference is a spring that keeps the clapper positively seated under static pressure so the alarm line stays dry until a sprinkler actually flows.
What is the retard chamber for?
The retard chamber is a small tank in the alarm trim between the valve and the gong/pressure switch. It absorbs brief pressure surges (water hammer from a pump kick, city-main transients) that would otherwise trigger false alarms. A drain orifice at the bottom lets surge water drain back out before it reaches the alarm devices. If the drain clogs with scale, the chamber can't drain fast enough and every surge becomes an alarm.
How often does an alarm check valve need an internal inspection?
Every 5 years per NFPA 25 §13.4.2. Open the bonnet, inspect the clapper facing, seat ring, hinge pin, and clapper spring for wear, corrosion, scale, or debris. Also clean strainers, filters, and restricted orifices in the alarm trim piping. External quarterly tests do NOT catch a grooved seat or a stuck hinge pin — the 5-year teardown is the only way.
What is the Tyco AV-1-300?
The Tyco AV-1-300 (now Johnson Controls) is a 300 psi / 20.7 bar alarm check valve available in 2½", 4", 6", and 8" sizes with flange, groove, or flange-groove end connections. Ductile-iron body, divided-seat ring, rubber-faced clapper, stainless hinge pin. One of the most commonly installed alarm check valves in North American wet sprinkler systems. Repair kits and clapper assemblies are available per size (see part number table above).
Why does my alarm check valve send false alarms?
Four common causes: (1) retard chamber drain clogged — water accumulates and triggers the gong on every small pressure surge. (2) Clapper seat corroded or grooved — water weeps past the clapper constantly, reaching the alarm port. (3) City-main pressure fluctuations exceed the retard chamber's absorption capacity. (4) Alarm test valve left partially open. All four are caught during the 5-year internal inspection and quarterly alarm test.

References

1. NFPA 13: Standard for the Installation of Sprinkler Systems, 2022 Edition, §8.16.

2. NFPA 25: Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems, 2023 Edition, Chapter 13 and §13.4.2.

3. UL 193: Standard for Alarm Valves for Fire Protection Service.

4. Tyco Fire Protection Products (Johnson Controls): AV-1-300 Alarm Check Valve datasheet — 300 psi / 20.7 bar, 2½"–8" sizes.

5. NFPA Fire Protection Handbook, 21st Edition, Section 14.

6. FM Global Property Loss Prevention Data Sheet 2-81: Fire Service Mains and Their Appurtenances.

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