Dry Alarm Check Valve

Dry Alarm Check Valve Definition and Components

A Dry Alarm Check Valve is the central control assembly for a dry-pipe fire sprinkler system. It is a specialized, differential-type valve that keeps water out of the system piping (which is filled with compressed air or nitrogen) until a sprinkler activates. Upon activation, it releases the air, allows water to enter, and triggers an alarm.

Key Terminology:

• Dry:For use in "dry-pipe" systems where the piping is filled with compressed air or nitrogen to prevent freezing.
• Differential Design:The valve clapper is designed with a larger surface area on the air (system) side than the water (supply) side. A small amount of "priming water" creates a seal, and the higher air pressure holds the clapper tightly closed against the incoming water pressure.
• Alarm:Incorporates ports that activate alarms when air pressure drops and water begins to flow.

Main Parts:

• Main Valve Body: Houses the differential clapper assembly.
• Differential Clapper & Seat: The core mechanism. A rubber-faced clapper with a larger diameter on the top (system side) than the bottom (supply side).
• Priming Water Reservoir: The space above the clapper is filled with a small amount of water to create an airtight seal.
• Air Pressure Gauge: Monitors the supervisory air pressure in the system piping (typically 20-40 psi).
• Water Pressure Gauge: Monitors the incoming water supply pressure.
• Intermediate Chamber (Alarm Port): A chamber between the clapper seat and the alarm line. When the clapper opens, water rushes into this chamber.
• Trim (Piping) Assembly: Includes the priming water level check valve, alarm line valve, drain valves, and connections for the air supply (exhauster/maintenance device).
• External Reset Mechanism: A handwheel or lever to manually reset the clapper after operation.

Role, Characteristics, and Application Scenarios of Dry Alarm Check Valve in Pipelines

Functions:

• System Sealing: Maintains a reliable air/water seal to prevent water from entering the dry piping.
• Quick Opening: Rapidly opens when air pressure drops to minimize water delivery time.
• Alarm Activation: Triggers hydraulic (water motor gong) and electrical (pressure switch) alarms upon water flow.
• System Reset: Allows the system to be drained, reset, and re-pressurized with air after operation.

Operational Features:

• Differential Principle: A small, constant air pressure (e.g., 20 psi) can hold back a much higher water pressure (e.g., 100 psi) due to the clapper's area differential.
• "Water Delivery Time" is Critical: Dry systems have a maximum allowable time for water to reach the most remote sprinkler (per NFPA 13). Valve design and system size are optimized for this.
• Priming Water Seal: Requires maintenance to ensure the proper water level is maintained to prevent air leakage past the clapper.
• More Complex than Wet Valves: Requires an air maintenance compressor or nitrogen supply and more involved testing.

Fire Sprinkler Alarm Check Valve Primary Usage Scenarios:

Used as the main control valve for dry-pipe fire sprinkler systems in unheated areas where water in the pipes would freeze (e.g., parking garages, warehouses, attics, freezers, loading docks).

Scenario Diagram:

Dry Alarm Check Valve Standards: Materials, Design, and Connections

How to Select Dry Alarm Check Valve

Step 1: Define Specifications from System Design

The valve is specified by the fire protection engineer based on complex calculations.

• Size & Orifice:Determined by hydraulic calculations to meet water delivery time Specify the orifice size (e.g., 1", 1-1/4") which is critical for dry valve performance.
• Listing Requirement:Must specify: "UL 260 Listed and/or FM Approved Dry Pipe Alarm Valve."
• Pressure Ratings:Specify both maximum water working pressure and maximum air working pressure.
• Trim & Accessories:Specify required trim (priming check valve, alarm line valve, drains) and required gauges. The Air Maintenance Device (compressor, air dryer, low-pressure switch) is typically a separate but coordinated purchase.
• Connection Type:Flanged, per riser diagram (e.g., ASME B16.1 Class 125).

Step 2: Source from Fire Protection Specialists

• Purchase only from authorized distributors of major fire protection manufacturers (e.g., Victaulic/Viking, Tyco, Reliable).
• Require a complete submittal package, including: UL/FM listing sheets, detailed dimensional drawings, water delivery time charts, and a schematic of the recommended trim.
• The engineer must review and approvethe submittal, ensuring the selected valve meets the calculated system demand.

Step 3: Order Execution

• The purchase order must reference the approved submittals.
• Consider lead times, as dry valves are less common than wet valves and may not be standard stock.

Pre-Shipment Inspection for Export Dry Alarm Check Valve and Key Considerations

Inspection Checklist:

Fire Valves Key Precautions for Export:

• Extreme Dryness is Non-Negotiable:After final testing, the valve must be thoroughly blown dry with compressed air and immediately sealed. Residual moisture will freeze and cause costly damage.
• VCI Protection:Use Vapor Corrosion Inhibitor (VCI) powder or spray inside the valve body to protect ferrous components from rust during ocean transit.
• Protect the Clapper Seat:The precision-machined seat is easily damaged. The shipping block must prevent any impact or vibration from causing the clapper to chatter against the seat.
• Separate Crate for Accessories:Pack sensitive accessories like the Air Maintenance Device, pressure switches, and gauges in their own, cushioned boxes. Do not leave them installed.
• Clear Documentation:Include a waterproof pouch inside the main crate containing the installation manual, test reports, listing card, and a specific warning about ensuring the valve is dry before storage or installation.

Dry Alarm Check Valve Size Chart