FM Global DS 3-11: Pressure Reducing and Flow Control Valves

In tall buildings the static pressure on lower floors can exceed the rating of system components. FM Global DS 3-11 (Flow and Pressure Regulating Devices for Fire Protection Service, October 2021, Interim Revision January 2023, 15 pages) covers the pressure reducing valves (PRVs) and automatic breach containment valves (ABCVs) used in that situation. It defines a PRV as a valve that reduces a high inlet pressure to a lower outlet pressure in both the static and flowing conditions, and treats “pressure-regulating valve” as a synonym (Section 1.0). Valves in fire pump installations are covered by DS 3-7, and preaction and deluge PRVs by DS 2-0.

The key warning is in Section 1.1: because PRVs work by restricting flow, they can obstruct the fire protection water supply, reducing sprinkler effectiveness or even preventing sprinklers and hoses from operating.

When a PRV Is Acceptable (2.3.2)

• No PRVs on sprinkler systems where the static inlet pressure is 175 psi (12.1 bar) or less (2.3.2.1).
• No PRVs in storage and manufacturing occupancies (2.3.2.2), and minimal use elsewhere (2.3.2.3). The example given is a high-rise: lower floors may need a PRV, upper floors where pressure is 12.1 bar or less do not, and additional fire pumps can reduce the number of PRVs.
• DS 3-7 2.2.2.3 takes the same line from the pump side: design high-rise systems so PRVs are not needed, and use FM Approved valves where unavoidable. Under DS 3-7 2.3.5.1, no PRVs on fire pump suction or discharge.
• No pilot-operated PRVs downstream of a dry-pipe or preaction valve, since the upper chamber must be full of water to work (2.3.2.5).
• Install in the orientation specified by the manufacturer; where settings are field-adjusted, keep the special tools on site under controlled access (2.3.2.6–2.3.2.7).

Valve Types (3.2)

• Direct-acting: an internal spring acts directly on the seat assembly, and the outlet pressure is adjusted by spring compression. Typically used as zone control valves within a sprinkler system. Some are factory-set and must be installed at the floor designated on their tag (3.3).
• Pilot-operated: a diaphragm-type automatic control valve with an adjustable pilot. The DS 3-11 glossary notes these are also called flow control valves or pressure control valves.
• Automatic breach containment valve (ABCV): closes fully once a pressure differential is exceeded. DS 3-11 does not allow ABCVs in fire protection systems and calls for existing ones to be removed (2.3.3.1), because a closure in anything other than a full breach impairs downstream protection (3.1).

Installation and Placards (2.2–2.3)

• All valves in dry areas readily accessible to personnel (2.2.1.1).
• Operation charts on site for every model; a permanent placard on each valve showing its set pressure, the flow and inlet pressure used for setting, and the sprinkler design flow and pressure at the outlet (2.3.1.1).
• In sprinkler systems (Figure 2.3.5.1-1): inlet and outlet gauges, waterflow alarm switch and an FM Approved relief valve, set below the rating of downstream components and at a point that reveals a malfunctioning PRV (2.3.5.2). The PRV must be full-flow testable at the highest system demand, by a permanent test line and drain, an inline meter or a clamp-on meter (2.3.5.3).
• In fire service mains (Figure 2.3.4.6-1): PRVs for non-fire water are kept separate from the fire system; a bypass loop the same size as the main, with a normally closed indicating control valve, surrounds the PRVs; check valves allow each PRV to be isolated; meters are on the outlet side (2.3.4.1–2.3.4.6).
• Where low flows risk water hammer, cavitation or poor regulation, or the valve’s minimum flow exceeds the alarm test flow, a secondary PRV is installed in parallel, sized for 125% of the primary’s minimum flow (2.3.4.4–2.3.4.5).
• On standpipes: PRVs at the hose outlets, with a valved gauge outlet upstream and a means of full-flow testing (2.3.6–2.3.7).

Sizing (3.3)

A PRV must keep the static outlet pressure below the component rating or the maximum system pressure allowed by DS 2-0, and under flow it must deliver the required flow and outlet pressure from the available inlet pressure. Consider the maximum static inlet pressure, maximum allowable static outlet pressure, minimum residual inlet pressure, minimum required residual outlet pressure, the range of flows and the different water supplies. Large valves may regulate poorly or cavitate at low flow, which calls for a smaller secondary valve in parallel. Brass or bronze bodies are preferred to limit corrosion and deposits.

Inspection and Testing (Table 2.4.1.2-1)

Activity	Frequency	Details
Visual inspection	Quarterly	Downstream pressure maintained as designed, signs of leakage; recorded on a form listing all PRVs, their location and area controlled
Partial-flow test	Annually	Flow through the inspector’s test connection or main drain downstream; confirm the valve lifts and maintains pressure flowing and at rest; record pressure and flow
Full-flow test	Every 5 years	Open the downstream main drain slowly until fully open; confirm and record that pressure is maintained

In high-rise buildings the drain riser must be able to take the test flow, or water can back up and exceed the design of the piping. All PRVs are tested on installation (2.4.1.1); changes in recorded inlet and outlet pressures are investigated and malfunctions corrected promptly (2.4.1.3–2.4.1.4). Form 2707 (Appendix C) records the annual performance test.

Quick Checklist

• PRV-free design attempted (extra pumps, zoning); PRVs only above 12.1 bar static inlet
• No PRVs in storage or manufacturing areas, or on fire pump suction or discharge
• No pilot-operated PRVs downstream of dry-pipe or preaction valves
• Permanent placard on each valve and operation charts on site
• Relief valve, gauges and full-flow test arrangement installed
• Quarterly visual, annual partial-flow and five-yearly full-flow tests recorded
• No ABCVs in the system

Frequently Asked Questions

When is a pressure reducing valve acceptable?

DS 3-11 limits rather than mandates PRVs. Under 2.3.2.1 no PRV is installed where the static inlet pressure is 12.1 bar (175 psi) or less; above that, PRVs are still not used in storage and manufacturing occupancies (2.3.2.2) and are minimised elsewhere (2.3.2.3). DS 3-7 2.2.2.3 asks first for a high-rise design that avoids PRVs, with FM Approved valves only where unavoidable.

What is the difference between direct-acting and pilot-operated PRVs?

Per DS 3-11 Section 3.2, a direct-acting PRV uses an internal spring acting directly on the seat, with the outlet pressure set by spring compression; it is typically used as a zone control valve. A pilot-operated PRV is a diaphragm control valve with an adjustable pilot, also called a flow control valve. Pilot-operated PRVs are not used downstream of dry-pipe or preaction valves (2.3.2.5).

What does DS 3-11 say about automatic breach containment valves?

Do not install them, and remove existing ones (2.3.3.1). Section 3.1 explains that an ABCV introduces unreliability: if it closes in any condition other than a full breach, downstream protection is impaired, while the most common water losses come from undetected leaks far smaller than a breach.

How often must PRVs be tested?

Per DS 3-11 Table 2.4.1.2-1: quarterly visual inspection, an annual partial-flow test and a full-flow test every 5 years through the downstream main drain. Each time, confirm and record that downstream pressure is maintained flowing and at rest, and investigate changes in the recorded pressures (2.4.1.3). The data sheet does not set a percentage deviation limit.

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