Priority Demand Valves for Fire Sprinkler Systems | Solenoid-Valve.World
Priority Demand Valves and BS 9251:2021
Priority demand valves are used within domestic and residential fire sprinkler systems to ensure that the available water supply is prioritised to the sprinkler system when required.
BS 9251:2021 defines a priority demand valve as a valve used to isolate the domestic water supply in the event of sprinkler operation.
For a BS 9251:2021 priority demand arrangement, the valve and associated control system must provide the required fail-safe operation:
✓ Automatic Domestic Water Isolation – When sprinkler operation is detected by the flow switch or associated alarm/control circuit, the priority demand valve closes automatically, isolating the domestic water supply so that the available water flow is prioritised to the sprinkler system.
✓ Fail-Safe Closure on Power Loss – The priority demand valve should fail to the closed position if electrical power is lost, preventing the domestic supply from competing with the sprinkler system for the available water supply.
✓ Latched Closure Following Sprinkler Activation – Following activation by the sprinkler flow switch, the domestic supply valve remains closed rather than automatically reopening when sprinkler flow stops.
✓ Manual Reset – Following sprinkler activation, the system requires manual intervention/reset before the domestic water supply is restored. This helps prevent the domestic supply from automatically reopening following a fire event or temporary interruption in sprinkler flow.
✓ Controller / Relay Integration – A priority demand valve should not be considered as a standalone valve installation. It forms part of a control arrangement incorporating the sprinkler flow switch, suitable control/relay circuitry and manual reset function.
What is a Priority Demand Valve (PDV)?
The Challenge in Combined Water Systems
In buildings where sprinkler systems share water supply, everyday water usage like kitchens, toilets, machine cooling and cleaning systems can inadvertently reduce available pressure to sprinklers during an emergency.
Valve-Based Solution for Fire Safety
A priority demand water valve automatically shuts off non essential water supply when the sprinkler system activates. This ensures maximum flow and pressure to fire sprinklers, stabilising system performance and safeguarding lives and property.
The Requirement.
BS9251 – the standard for ‘fire sprinkler systems for domestic and residential occupancies’ – states that if the mains water supply flow rate available to the fire sprinkler system is liable to be affected by domestic water usage (e.g. shower, washing machine etc), THEN a valve must be fitted to cut off supply for domestic use in the event of a sprinkler activation.
Why the Controller is Important
A normally closed solenoid valve or fail-safe motorised valve can provide the physical isolation of the domestic water supply, but the valve alone does not provide the complete priority demand control function.
The control system receives the signal from the sprinkler flow switch and controls the priority demand valve so that the domestic supply is automatically isolated when sprinkler operation occurs.
For BS 9251:2021 applications, the control arrangement should be designed so that sprinkler activation causes the domestic valve to close and remain closed until the system is manually reset.
Fail-Safe Operation
During normal operation, the domestic water supply remains available.
Normal condition → Domestic supply OPEN
Sprinkler flow detected → Domestic supply CLOSED
Electrical power failure → Domestic supply CLOSED
Sprinkler flow stops → Domestic supply remains CLOSED
System manually reset → Domestic supply OPEN
This fail-safe arrangement ensures that a loss of electrical power or cessation of sprinkler flow cannot automatically restore the domestic water supply following sprinkler activation.
Important Installation Note
Compliance with BS 9251:2021 relates to the design and installation of the complete residential sprinkler system and not simply to the selection of an individual valve.
The priority demand valve, flow switch, controller, electrical wiring, water supply and sprinkler system should therefore be specified, installed, commissioned and tested by a suitably competent fire sprinkler system designer or installer in accordance with the applicable requirements of BS 9251:2021.
Recommended Valve Setup for Priority Demand Systems
| Application | Recommended Product Type | Why It Works |
|---|---|---|
| Small residential or light commercial building | WRAS solenoid valve (brass) | Compact, cost-effective, and instantly responsive |
| Larger installations or where flow modulation is needed | WRAS motor-actuated ABV ball valve | Fast actuation, robust control, tailor-made for priority demand systems |
1. Purpose of the Priority Demand Valve
A PDV automatically restricts or shuts off non-sprinkler domestic water demand when the fire sprinkler system activates.
This ensures the sprinklers receive sufficient flow and pressure, even if household fixtures are being used at the same time.
Required in many domestic/residential systems supplied from a shared incoming main.
2. Key Installation Principles
Location: Install the PDV on the incoming cold-water main, downstream of the mains stop tap, before any branches to domestic services.
Bypass: The domestic services should connect through the PDV, while the sprinkler connection bypasses it.
Activation: The valve is triggered by a flow switch or pressure drop when the sprinkler system operates.
3. Typical Installation Layout
1. Incoming mains enters the property → Stop tap → Double check valve (as required by local water regulations).
2. From this point, pipework splits.
>Fire sprinkler supply: Direct line (uninterrupted).
>Domestic supply: Routed through the PDV.
3. PDV operation:
In normal conditions: Allows water through to domestic outlets.
On sprinkler activation: PDV closes/restricts domestic line, prioritising sprinkler flow.
4. Installation Steps
Shut off water supply and drain down the system.
Identify the main supply pipe immediately after the incoming stop tap and back flow prevention device.
Install a T-connection:
One leg to the sprinkler system (unrestricted). One leg to the PDV (serving the domestic water system).
Fit the PDV according to manufacturer instructions (orientation and flow direction are critical).
Reconnect domestic supply downstream of the PDV.
Check settings/commissioning:
Ensure the PDV activates at the correct pressure/flow.
Test both domestic supply and sprinkler priority function.
Label the installation: Clearly identify sprinkler supply, PDV, and isolation points.
5. Compliance & Best Practice
Follow manufacturer’s installation guide – each PDV may have specific requirements.
Check local regulations – in the UK, installations must comply with BS 9251 (sprinklers) and Water Supply (Water Fittings) Regulations.
Access: Ensure the PDV is accessible for inspection, testing, and maintenance.
Testing: Regular functional testing should be part of the sprinkler system maintenance plan.
Summary
Priority demand water valves are essential for maintaining water pressure in fire sprinkler systems shared with domestic supply.
Our WRAS solenoid valves and WRAS motor-actuated ball valves are tailored for rapid, reliable prioritisation.
Flexible materials and valve types ensure compatibility across diverse systems.
Easy installation and trust in compliance make your fire safety system robust and effective.
View our Priority Demand Solenoid Valves.
Priority Demand 2/2 Normally Closed (Failsafe Closed - Power to Open)
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