Sprinkler System Valves: Alarm Check, Dry Pipe, Deluge and Pre-Action Explained

Quick Answer

A sprinkler riser carries a control valve, a system valve and alarm devices. The control valve, an OS&Y gate valve, a supervised butterfly valve or a buried NRS gate valve with an indicator post, must be kept open and supervised. Wet systems use an alarm check valve: flow lifts its clapper and sends water to a water motor gong and pressure switch, through a retard chamber where supply pressure varies. Dry pipe systems hold water back with air or nitrogen on a differential dry pipe valve (on one common design, 1 bar of air holds back 5.5 bar of water), with quick-opening devices on larger systems. A deluge valve feeds open sprinklers or nozzles and is opened by detection, so every nozzle flows at once. A pre-action valve feeds closed sprinklers and, in NFPA 13's terms, admits water on detection (single interlock), on detection or sprinkler operation (non-interlock), or only on both (double interlock). Specify UL listed or FM approved models. NFPA 25 (2017 edition) calls for an annual trip test of dry pipe valves and a full-flow trip test every three years.

A typical sprinkler valve enquiry gives a size and a type, "DN150 alarm valve, flanged", and nothing else. The valve must also suit the system type, the supply pressure and its variation, the trim, the release method and the approvals the insurer and authority accept. A wet alarm valve sent to a cold store is found at commissioning, when it is expensive to fix.

This guide covers each riser valve, how the four system valves work, and how they are supervised, approved, tested and ordered.

The riser and its valves

• Water supply: town main, tank or fire pump, with a backflow preventer where required and pressure-reducing valves where supply pressure exceeds component ratings
• Control valve: shuts the system off for maintenance
• System valve and trim: alarm check, dry pipe, deluge or pre-action valve, with the maker's gauges, drains, test valves and alarm piping
• Alarm devices: water motor gong, alarm pressure switch, flow switch and supervisory switches
• Piping and sprinklers, with an inspector's test connection (at the most remote point on dry systems)

See also our guide to industrial fire protection systems.

System types and where each fits

Control valves: OS&Y, NRS and supervised butterfly

A closed control valve disables every sprinkler downstream, so its position must always be known.

• OS&Y (outside screw and yoke) gate valve: the stem rises as the valve opens, so its position shows from across the room. Used at risers, tank outlets and fire pump suction and discharge. Fire-service gate valves are listed to UL 262.
• NRS (non-rising stem) gate valve: the stem turns without rising, so the valve shows nothing. On buried mains it carries an indicator post (UL 789) that reads OPEN or SHUT at ground level.
• Supervised butterfly valve: a gear operator with a position indicator and a supervisory (tamper) switch that signals the panel when the valve leaves fully open. Compact, but with more pressure loss than a gate valve; see butterfly valve vs gate valve. Listed to UL 1091.

NFPA 13 (2022 edition, 16.9.3.3.1) accepts four supervision methods: electrical supervision to a central, proprietary or remote station; a local signal at a constantly attended point; locking the valve open; or, in a fenced enclosure under the owner's control, sealing it open with weekly inspection. Only electrical supervision reports a closing valve as it happens.

Alarm check valves (wet systems)

An alarm check valve is a check valve with an alarm port. Its clapper rests on a seat ring grooved to the alarm outlet; when a sprinkler opens, flow lifts the clapper and sends water down the alarm line to:

• Retard chamber: a small vessel that fills while draining through a restriction, 1/8 in (3.2 mm) on one maker's design. A brief surge drains away; sustained flow fills it and pressurises the devices beyond. Makers describe it as required where pressure varies, typically on public water supplies
• Water motor gong: a water wheel that drives a striker against a gong outside the building, with no electricity
• Alarm pressure switch: signals the fire alarm panel

Many wet systems use a plain check valve with a vane-type flow switch instead: a paddle deflects with flow and, after a time delay that rides out surges, signals the panel. Vane switches belong on wet systems; the rush of water when a dry or deluge valve trips can tear the paddle.

Dry pipe valves

How the differential works

A dry pipe valve, sold by some suppliers as a dry alarm valve, keeps water out of piping that could freeze. The clapper's air-side seat is much larger than its water seat, so modest air pressure holds back far higher water pressure. An intermediate chamber between the seats, at atmospheric pressure, feeds the alarm line. When a sprinkler opens, air escapes, pressure falls below the trip point, and water lifts the clapper and floods the piping and alarm line.

The differential is the ratio of water pressure to holding air pressure, 5.5:1 on one common valve, and the trip pressure is the supply pressure divided by it. NFPA 13's generic rule sets the air 20 psi (1.4 bar) above the calculated trip pressure, but the maker's air-pressure table takes precedence. Many newer valves add a mechanical latch, and low-pressure designs run on much less air, so the generic margin would set them too high.

Worked example: setting the air pressure

A 5.5:1 valve on a 100 psi (6.9 bar) supply:

• Trip pressure: 100 ÷ 5.5 = 18.2 psi (1.25 bar)
• Generic rule: 18.2 + 20 = 38.2 psi (2.63 bar)
• One maker's table for a 5.5:1 valve at 100 psi: 25–33 psi (1.7–2.3 bar)

Extra air must bleed out through the opened sprinkler before the valve trips, so excess air means later water. Base the setting on the highest supply pressure and follow the maker's table.

Quick-opening devices and system size

Quick-opening devices shorten the bleed-down on large systems. An accelerator senses the fast pressure drop and feeds system air into the intermediate chamber, destroying the differential; an exhauster vents system air to atmosphere.

NFPA 13 ties them to volume. In the 2019 edition's terms, a system of up to about 500 US gal (1,893 l) needs no quick-opening device and no delivery-time check; up to 750 gal (2,839 l) is treated the same way with one; larger systems must show, by test or calculation, that water reaches the inspector's test connection within the time set for the hazard. Check the edition your authority enforces.

Worked example: is the system too big?

A cold-store dry system, with internal diameters from ASME B36.10M (see our pipe schedule chart) and volume per metre = π/4 × ID²:

At 788 gal the system exceeds 750 gal even with a quick-opening device, so its delivery time must be proven. Two dry valves, each serving about half (roughly 1,490 l or 394 gal), would each fall inside the 500 gal threshold.

Air supply and valve room

• NFPA 25 expects the air supply to restore normal pressure within 30 minutes after a trip test (60 minutes for refrigerated spaces below −15 °C, 5 °F)
• Keep the valve in a heated space: NFPA 25 has freezing-prone valve enclosures checked daily in cold weather for at least 4 °C (40 °F)
• Older valves need priming water; the US National Fire Sprinkler Association notes that NFPA 25 calls for quarterly level checks, since a water column above the clapper affects tripping

Deluge valves

A deluge valve feeds open sprinklers or spray nozzles, so every one discharges when it opens. Most are hydraulically operated: supply water, admitted through a restriction, pressurises a priming chamber that holds the valve shut. Venting the chamber faster than the restriction refills it lets supply pressure open the valve. Release is by:

• Electric detection: a solenoid valve opened by a releasing panel listed for releasing service
• Wet or dry pilot lines with closed pilot sprinklers, which drain or vent when one opens
• Manual emergency release at the valve or a remote station

Water spray systems for special hazards such as transformers and tank farms are designed to NFPA 15, and foam systems add a proportioner downstream. For conveyors carrying combustible dust, see our guide to combustible dust.

Worked example: deluge flow

Each open sprinkler discharges Q = K√P. Take 24 open sprinklers of K80 (l/min per bar^½; K5.6 in US units, the metric K being 14.4 times the US figure):

• At an assumed 1.4 bar (20 psi) at the remote end: 80 × √1.4 = 94.7 l/min (25 gpm) each, 2,272 l/min (600 gpm) in total
• If the nozzles average 1.8 bar: 80 × √1.8 = 107.3 l/min each, 2,576 l/min (680 gpm)

Flow rises with the square root of pressure: doubling it from 1.4 to 2.8 bar adds only 41%. A closed-sprinkler system flows only from heads the fire opens (twelve K80 heads at 1.4 bar give 1,136 l/min); a deluge valve opens all 24, so valve, pipe and supply must carry the full flow.

Pre-action valves

Many pre-action valves are a deluge valve with a check valve above it and trim that adds the interlock. NFPA 13 (2019 edition, 8.3.2.1) defines three types:

• Single interlock: admits water to the sprinkler piping upon operation of detection devices; a knocked sprinkler or leaking joint releases only air
• Non-interlock: admits water upon operation of detection devices or automatic sprinklers
• Double interlock: admits water upon operation of both detection devices and automatic sprinklers

The same edition requires automatic supervision of piping and detection on systems with more than 20 sprinklers, supervising air or nitrogen of at least 7 psi (0.5 bar) on all pre-action systems, and thermal release devices that operate below the sprinklers' temperature.

Single interlock suits data centres, archives, museums and libraries. Double interlock was designed for freezer warehouses, where water admitted on a false detection would freeze in the pipe. The cost: water waits until a sprinkler opens and its air escapes, delaying it on a real fire.

Approvals: what UL listing and FM approval mean

• UL listing: UL tests a representative sample against a UL standard and audits production under its follow-up programme. Standards include UL 193 (alarm valves), UL 260 (dry pipe and deluge valves), UL 262 (gate valves) and UL 1091 (butterfly valves) for fire-protection service; listings appear in UL's online certifications directory
• FM approval: FM Approvals, part of FM (formerly FM Global), tests to its own approval standards, audits production and lists approved products in the FM Approval Guide
• Europe: the EN 12259 series covers sprinkler components, such as EN 12259-2 for wet alarm valve assemblies, certified by bodies such as LPCB or VdS
• Model-specific: a listing covers one maker's model in stated sizes, pressures, orientations and trim; check the model number in the directory and buy trim and spares for the listed assembly

In NFPA usage, "approved" means acceptable to the authority having jurisdiction, not FM Approved.

Testing and inspection (NFPA 25)

Selected intervals from the 2017 edition of NFPA 25; check the edition your authority enforces:

At each full-flow test, record trip time and water delivery time to the inspector's test connection, as NFPA 25 requires, and compare them with the acceptance test; investigate any significant change. Never grease dry valve seats.

Common Mistakes

1. A wet alarm valve where pipes can freeze. Ice splits pipes and fittings, and a frozen system cannot discharge.

   Prevention: Use dry pipe or pre-action systems where pipes can freeze, and keep the valve itself in a heated room.

2. No retard chamber on a variable-pressure supply. Surges ring the gong until someone silences the alarm.

   Prevention: Fit the retard chamber and restriction the maker's trim chart shows for variable pressure.

3. Setting dry system air by habit. Too much air delays the trip; too little risks false trips at peak supply pressure.

   Prevention: Set the air from the maker's table; use the generic 20 psi margin only where the maker gives none.

4. A dry system too large for its valve. Water reaches the remote sprinklers too late.

   Prevention: Calculate system volume early; add a quick-opening device, prove the delivery time or split the system.

5. Control valves left partly closed or unsupervised. Every sprinkler downstream is out of service.

   Prevention: Supervise control valves electrically where possible, and operate and inspect them on the NFPA 25 schedule.

6. Treating approvals as interchangeable. Trim or parts from outside the listed assembly void the listing.

   Prevention: Get model numbers, check them in the UL or FM directory, and buy trim and spares for the listed assembly.

7. A deluge supply sized for a few heads. All nozzles open together; an undersized supply starves the remote ones.

   Prevention: Calculate the flow of every nozzle at its pressure and check the supply and fire pump against the total.

What to send for a quotation

• System: wet, dry pipe, deluge or pre-action (single, double or non-interlock); design standard (NFPA 13, EN 12845 or the insurer's)
• Hazard: occupancy, storage, ambient temperature range, freezing risk
• Valve: size, end connections (flanged, grooved or mixed), orientation, pressure rating
• Water supply: static and residual pressure, maximum pressure, whether it varies
• Dry and pre-action: system volume, air or nitrogen source, quick-opening device, low-air supervision
• Release (deluge and pre-action): electric (panel and solenoid voltage), wet or dry pilot, manual; foam if required
• Trim and devices: water motor gong, pressure and flow switches, gauges, drain and test valves, supervisory switches
• Approvals: UL, FM, LPCB or VdS, as the insurer and authority require

Supply from Kasko Makine

Kasko Makine supplies sprinkler system valves and devices:

• Dry alarm valves: for dry pipe systems in areas exposed to freezing, such as cold stores, unheated warehouses and parking garages; the page lists a valve body, water motor alarm gong and pressure switch, for installation where the valve cannot freeze
• Deluge valves: quick-release, hydraulically operated diaphragm valves, opened when a detection device vents the top chamber; for open sprinklers or nozzles, with optional foam proportioning
• Pre-action systems: released by wet or dry pilot lines and/or electrical detection; flanged × flanged, flanged × grooved or grooved × grooved; vertical or horizontal installation; DN40–DN200 (1½–8 in); working pressure 12.1–17.2 bar (175–250 psi)
• OS&Y rising stem valves: gate valves with threaded, flanged or grooved ends; DN25–DN400 (1–16 in); 12.1–24.1 bar (175–350 psi); ASTM A536 nodular iron body and cover, AISI 420 stainless spindle, EPDM-covered wedge and EPDM seals
• NRS non-rising stem valves: flanged gate valves for underground mains with post indicators; DN65–DN400 (2½–16 in); 13.8–20.7 bar (200–300 psi); OS&Y materials
• Watch switched butterfly valves: tamper switch, handwheel and gearbox; threaded, wafer or grooved; DN25–DN300 (1–12 in); 12.1–20.7 bar (175–300 psi); ASTM A536 nodular iron body, nickel-coated disc
• Flow switches: for wet pipe systems; threaded (DN25–DN50, 1–2 in) or U-bolt (DN50–DN200, 2–8 in) mounting on SCH 10 to SCH 40 steel pipe
• Sprinklers for wet, dry pipe, deluge and pre-action systems, and ESFR sprinklers for high-piled storage without in-rack sprinklers

The pages for the pre-action systems, OS&Y and NRS valves, watch switched butterfly valves and flow switches list UL, ULc and FM approvals. Approvals belong to specific models: ask for model numbers and check them in the UL and FM directories.

Engineering support: Send the system type, hazard, riser size, water supply data and required approvals. We will review valve type, trim and alarm devices against your data and quote them together.

Send the system type, hazard, riser size, water supply pressure and required approvals for a valve and trim quotation — we reply within 24 hours. Reach us at info@kaskomakine.com or WhatsApp +90 (537) 521 1399.

Continue Reading

• Industrial Fire Protection Systems: Sprinklers, Foam, Gas and Hydrants
• Fire Pumps (NFPA 20): Types, Performance Requirements & Selection
• Butterfly Valve vs Gate Valve: 8 Key Differences & Which to Choose
• Check Valves: Types, Selection & Water Hammer Prevention

Frequently Asked Questions

Q: What valves are installed on a sprinkler system riser?
A: A riser normally has a control valve, a system valve and alarm devices. The control valve is an OS&Y gate valve, a supervised butterfly valve or, underground, an NRS gate valve with an indicator post. The system valve is an alarm check, dry pipe, deluge or pre-action valve. Alarm devices include a water motor gong and pressure or flow switches.

Q: How does an alarm check valve work?
A: An alarm check valve is a check valve with an alarm port. When a sprinkler opens, flow lifts the clapper and uncovers a groove that sends water to the alarm line. A retard chamber there absorbs brief pressure surges; sustained flow fills it and operates the water motor gong and pressure switch. It is needed where supply pressure varies.

Q: How does a dry pipe valve work?
A: A dry pipe valve holds water back with compressed air or nitrogen in the sprinkler piping. Its clapper is larger on the air side than on the water side, so on one common design 1 bar of air holds back 5.5 bar of water. When a sprinkler opens, air escapes, pressure falls below the trip point and water opens the valve.

Q: What is the difference between a deluge system and a pre-action system?
A: A deluge system uses open sprinklers or nozzles, so when detection opens the deluge valve, every nozzle discharges at once; it suits fast-spreading hazards such as transformers and flammable liquids. A pre-action system uses closed sprinklers: the valve admits water to the piping on detection, sprinkler operation or both, but water discharges only from sprinklers opened by heat.

Q: What is the difference between single interlock and double interlock pre-action?
A: NFPA 13 defines a single interlock system as admitting water to the sprinkler piping on operation of detection devices, and a double interlock system as admitting it only when both detection devices and automatic sprinklers operate. Single interlock suits data centres and archives. Double interlock suits freezers but delays water until a sprinkler has opened.

Q: What does UL listed or FM approved mean for a sprinkler valve?
A: It means a specific model has been tested to a published standard and its production is audited. UL lists valves to standards such as UL 193 (alarm valves) and UL 260 (dry pipe and deluge valves); FM Approvals publishes approved products in its Approval Guide. Listings are model-specific, so check the model number before ordering.

Q: How often must a dry pipe valve be trip tested?
A: Under the 2017 edition of NFPA 25, each dry pipe valve is trip tested annually in warm weather. Every three years, and whenever the system is altered, the test is a full-flow trip test with the control valve fully open and any quick-opening device in service. Quick-opening devices themselves are tested quarterly.