It detects that water has started moving and passes water into the alarm line - it does not hold anything back.

In a wet system the pipework is permanently full of water up to the sprinkler heads.

The valve is a one-way clapper with an alarm connection above its seat.

When a head operates, flow lifts the clapper and water reaches the alarm line.

That drives a water motor gong, a pressure switch, or both.

The simplicity of the arrangement is why wet systems are the most reliable type.

Stopping brief supply pressure surges from ringing the alarm.

Small surges lift the clapper momentarily even though no sprinkler has operated.

The retard chamber must fill before the alarm line pressurises, and it drains continuously.

A brief surge fills it slightly and it empties again; sustained genuine flow fills it and the alarm sounds.

Without a retard, a system on a variable supply would alarm regularly.

It introduces a short deliberate delay, which the design accepts in exchange for reliability.

Usually a blocked retard drain or a genuinely variable water supply.

A blocked drain leaves the chamber partly full, so small surges accumulate into an alarm.

A drain that passes too freely can delay or lose a genuine alarm instead.

Municipal supply fluctuation, pump starts elsewhere and large valves closing all produce surges.

Where surges are frequent, an excess pressure arrangement or a different supply detail may be the real fix.

Treating recurrent false alarms as a nuisance rather than a fault is how systems end up with disabled alarms.

Through the inspector's test connection - a pipe with an orifice sized to simulate one sprinkler operating.

It is positioned remotely from the riser so the test exercises the whole path.

Opening it should produce an alarm within the time the local regime specifies.

That is the only routine proof that detection, alarm valve, switch and panel all work together.

Discharge from the test connection has to go somewhere, which is a design detail.

How often, and what counts as a pass, come from whichever standard applies where the building is.

A mechanical alarm driven by the water itself, needing no electrical supply.

Water from the alarm line drives a turbine that strikes a gong externally.

Because it needs no power, it works when the building's electrical supply has failed.

It is loud, distinctive and mounted outside so it can be heard on approach.

Modern installations usually pair it with a pressure switch feeding the fire alarm panel.

Its drain must be clear or the gong sounds continuously after a test.

Anywhere the water can get cold, yes - which is why parts of an otherwise wet building use dry sprinklers or a dry system.

A wet system is only suitable where the whole protected space stays above freezing.

Loading docks, canopies, unheated lobbies and roof voids are the usual exceptions.

Dry sprinklers extend a wet system into those small cold areas.

For a wholly unheated building, a dry pipe system is the answer instead.

A frozen wet system can split pipework, which causes far more damage than the fire risk it was addressing.

Exercising the test and drain functions, checking gauges, and keeping the retard drain clear.

Gauge readings above and below the clapper indicate whether the valve is seated and the supply is healthy.

The retard drain is small and is the component most likely to block.

Internal inspection of the clapper and seat is required periodically in most regimes.

Debris and corrosion products from the pipework collect at the seat.

Intervals, competencies and records are set by the local standard rather than by the manufacturer alone.