Quick answers
What is backflow in a fire sprinkler system?
Backflow is when water flows in the opposite direction to where it should go, for example from the sprinkler line back toward the municipal water source. Backpressure or backsiphonage can reverse the flow.
Why does a fire sprinkler line need a backflow preventer?
Water that has been sitting in sprinkler pipes for a long time could be harmful to drink. A backflow preventer protects the public or internal potable-water supply from that reverse flow.
Is a backflow test the same as a sprinkler forward-flow test?
No. The performance test checks the check valves and, for a reduced-pressure assembly, the relief function. The forward-flow test shows the fire system can receive the required water through the assembly. They are related but not interchangeable.
Can I close a sprinkler valve to stop unexpected water flow?
Do not close sprinkler or backflow isolation valves to stop noise or water unless the authorised emergency procedure directs it. Treat an unexpected sprinkler alarm or flow as a possible fire, evacuate and call 112 if fire or smoke is suspected.
Many buildings take water for their sprinkler system straight from the municipal main, or share a line with the drinking-water supply. That connection brings a hidden risk. The water sitting in sprinkler pipes is stale, can be rusty and may carry chemicals or antifreeze. If it flows backwards into the drinking-water line, people can fall ill. A backflow preventer stops that. This page explains what it is and how it should be tested, for facility managers, society committees and maintenance teams.
What is backflow?
Backflow is water flowing the wrong way, from the sprinkler line back towards the water supply. It happens in two ways:
- Backpressure: the pressure in the sprinkler system rises above the supply pressure, for example when a fire pump runs or water is pumped in from a tank on the roof.
- Backsiphonage: the supply pressure suddenly drops, for example when a main bursts or the municipal supply is cut, and water is sucked back out of the building’s pipes.
The Central Public Health and Environmental Engineering Organisation (CPHEEO), in its water-supply manual, notes that contamination from backflow can be prevented by fitting double check or non-return valves.
The two common types
- Double check valve assembly. Two check valves in a row, with test cocks. It is used where the risk to drinking water is lower, such as a plain water sprinkler system.
- Reduced-pressure-principle (RPZ) assembly. Two check valves with a relief valve between them that dumps water to drain if either check valve leaks. It is used where the risk is higher, for example where chemicals or additives are in the system. Because it discharges water from its relief opening, it needs a drain that can take that water without flooding an electrical room or an occupied area.
Which type you need depends on the hazard, the water utility’s rules and the approved fire design. Do not choose one just by pipe size.
Two tests that are often confused
There are two different tests on the same device. Each answers a different question, and passing one does not prove the other.
- Backflow performance test. Does the device protect the drinking water? A qualified tester uses calibrated gauges to check that each check valve holds and, on an RPZ, that the relief valve opens when it should.
- Forward-flow test. Can enough water get through the device to fight a fire? Water is run through the assembly at the flow the sprinkler system was designed for, including hose demand where hydrants or hose reels are downstream. A device can be watertight in the backflow direction and still choke the flow the sprinklers need.
In the US, NFPA 25 asks for a forward-flow test once a year at the system’s design flow. That is a US rule. In India there is no single nationwide test frequency for sprinkler backflow devices in the public sources we checked. The interval, the type of assembly accepted and who may test it are set by your local water utility, the fire authority, the approved design and the standard adopted for your building. Sprinkler design in India follows BIS IS 15105:2021 and the National Building Code.
Doing the test safely
A badly planned test can do as much harm as a fire. Running water can set off the alarm, start the fire pump and flood a basement. A valve closed for testing can leave the building without sprinklers if nobody remembers to open it again.
- Plan where the test water will go before any valve is opened.
- Tell the alarm monitoring centre, the building team and anyone affected.
- Use a written impairment permit for any valve you close, with someone named to restore it.
- Photograph and record every valve position before and after.
- Have a second person check that every valve is back open and the system is back in service.
- Keep the signed test report with the fire system records.
Look at the device itself regularly: check for leaks, damage, a dripping relief valve or a blocked drain, and have faults repaired quickly.
If water starts flowing unexpectedly
Treat a sprinkler alarm or sudden water flow as a possible fire until someone confirms otherwise. If there is fire or smoke, get out and call 101 or 112. Do not close sprinkler or backflow valves just to stop the noise or the water, unless your emergency procedure tells an authorised person to do so.
This week, ask your maintenance team for the last test report. Check whether it covers both the backflow test and the forward-flow test, and who signed it.
What needs attention
- Backflow prevention protects the public or building drinking-water supply from water flowing the wrong way
- A device that passes a backflow test may still cause too much pressure loss when fire flow is needed
- A forward-flow test does not prove that every check valve or relief valve passes the backflow test
- A closed or half-closed valve can defeat the sprinklers even when the assembly itself is fine
- Reduced-pressure assemblies discharge water from their relief opening and need a drain that cannot flood electrical or occupied areas
- Test water can set off alarms, start pumps and cause damage unless the test is coordinated
- Changes in pressure zones, pumps, roof tanks and industrial processes can create backpressure
Controls that reduce risk
- Find the sprinkler backflow assembly and confirm its make, type, size and direction of flow
- Get the approved hydraulic design and the flow required at the test point
- Ask the water utility and fire authority which test intervals and tester qualifications apply
- Check that test ports, gauges, the flow path and the drain can be reached
- Write an impairment and restoration checklist before anyone touches a control valve
- Coordinate with the alarm monitoring centre, the fire pump operator, the building team and affected occupants
- Record valve positions and monitoring status before and after the test
- Repair failures quickly and keep the signed test report with the fire system records
Common unsafe practices
- Treating the backflow performance test and the forward-flow test as the same thing
- Choosing an assembly only by pipe size, without a hazard assessment or hydraulic calculation
- Assuming a double check assembly is acceptable for every sprinkler connection
- Closing control valves without an impairment permit, telling people or arranging temporary protection
- Running water before checking that the drain can take it and that it goes somewhere safe
- Silencing alarms or switching off pumps and forgetting to restore them
- Accepting a visual check in place of a calibrated field test where testing is required
- Treating a foreign once-a-year rule as Indian law without checking with the local authority
Leave a comment