EN 12845 Control Valve Set, Stop Valves and Alarm Valve Arrangement

The anatomy of the control valve set: why the stop valve must be OS&Y or monitored, choosing between wet, dry, alternate and pre-action alarm valves, drains and test connections, tamper switch monitoring, and the "dead installation" error seen most often on site.

On an annual inspection at a textile warehouse we noticed something: the butterfly stop valve on the main control valve set showed its indicator arrow near the closed position, and the locking chain on the valve lever had secured it, by mistake, half shut. The installation had been running on half its water for three months and nobody had noticed — because it was not a monitored butterfly: no tamper switch, no rising stem. The control valve set clause in EN 12845 exists to prevent exactly this: stop valve, alarm valve, drain and test connections are designed as one assembly, with each part checking the others. This article opens the control valve set piece by piece.

What a control valve set is

EN 12845 defines the control valve set as the assembly comprising the alarm valve, the stop valve and all associated valves and accessories needed to operate the installation. One set per installation is mandatory, and its components must be certified to EN 12259-2 (wet alarm valve assemblies) or EN 12259-3 (dry alarm valve assemblies). An alarm valve alone, or a stop valve alone, is not a control valve set; it is expected to be supplied as a complete certified assembly.

A typical wet set is built on the riser in this order, top to bottom:

• Installation-side pressure gauge, above the alarm valve
• Wet alarm valve (clapper and body)
• Supply-side pressure gauge, below the alarm valve
• Main stop valve (OS&Y or monitored butterfly)
• Water supply connection (suction or pump discharge)
• Branches: alarm test valve, main drain valve, retard chamber, water motor alarm line, pressure switch

The order is not accidental. With the stop valve at the bottom, closing it allows the whole installation above to be drained for service; the gauge between alarm valve and stop valve reads the supply-side pressure independently. The gauge above gives the installation-side pressure; the difference between the two shows up as clapper loss and static head difference.

The stop valve: three golden rules

Three conditions apply to every stop valve capable of shutting off water to sprinklers:

1. It closes clockwise — standardised so that an operator under pressure turns it the right way.
2. It has a position indicator — open or shut must be clearly readable by eye. An OS&Y gate valve shows its stem outside, visible from a distance; a butterfly relies on the indicator arrow on the body, and that lever can mislead mechanically, so the monitored version is preferred.
3. It is strapped and padlocked, or equivalently secured, in the correct position. The word "correct" is critical: usually that means open, but where a line is held shut for testing after draining, that position is what gets secured.

The standard also states that no stop valve is fitted downstream of the control valve set — with the exception that a monitored stop valve may be fitted for ease of maintenance. "Monitored" means a tamper switch mounted on the valve that produces an electrical signal on the smallest movement of the spindle towards closed.

OS&Y or monitored butterfly?

Both are accepted on site; the choice usually comes down to space and cost. The advantage of an OS&Y gate valve is that the position cannot be faked mechanically — the stem is out where you can see it. The disadvantages: it takes space, it is heavy and expensive, and large sizes need a gearbox to operate. A monitored butterfly is compact, light and cheap; but if the tamper switch fails, position is judged only by eye, and you fall into the half-shut trap described above. So where a monitored butterfly is chosen, wiring the tamper signal to the fire alarm panel and testing it is not negotiable.

Choosing the alarm valve type

EN 12845 defines four basic alarm valve types:

Type	Holding medium	Typical use	EN 12259
Wet	Water	No freezing risk, normal buildings	Part 2
Dry	Compressed air or nitrogen	Cold stores, car parks, roof voids	Part 3
Alternate	Water or air by season	Buildings wet in summer, dry in winter	Parts 2 and 3 combined
Pre-action	Air plus independent detection	Data centres, archives, museums, where accidental discharge is unacceptable	Part 3 (special)

A wet alarm valve works on a pressure balance: supply pressure below tries to lift the clapper, while installation pressure above — the water column plus the retard chamber — holds it shut. When a sprinkler opens, the pressure above falls, the balance breaks, the clapper lifts, water passes and the alarm line is fed. A retard chamber is added so that pump pressure fluctuations do not produce false alarms; it absorbs brief low-flow pressure drops while passing the continuous flow of a genuine sprinkler operation.

In a dry valve the balance is reversed: a modest air pressure (2–3 bar) over a much larger clapper area holds back a much higher water pressure (around 10 bar) — the differential design. That is why a maximum pressure indicator (drag pointer) is added to the gauge on a dry valve, so that any unexpected water entry into the dry side leaves a trace.

Drain and test valves

The drain valve does more than empty the installation for maintenance; it also performs the main drain test below the alarm valve. Fully opened, the flow passing from the supply side is measured together with the drop on the supply gauge — the simplest test of whether the water supply still delivers its expected capacity.

Section protected by the drain valve	Min. size (mm)
LH installation	40
OH / HHP / HHS installation	50
Subsidiary installation	50
Zone	50
Trapped distribution pipe, ≤ DN80	25
Trapped distribution pipe, > DN80	40
Trapped range pipes	25
Test pipe between dry/alternate valve and the stop valve below	15

The drain outlet sits no more than 3 m above floor level and is plugged. Visibility matters too — the operator must see the water actually flowing during a test; routing it into a drain out of sight is not enough.

The 15 mm test valves:

• Alarm test valve — draws water from just below the wet alarm valve to test the water motor gong and the electrical pressure switch. It simulates the flow of a single sprinkler.
• Pump start test valve — tests the jockey and start arrangement that triggers the pump remotely.
• For dry, alternate and pre-action sets, a separate test valve feeding the alarm line from below the main water stop valve is also required; the alarm valve is dry above, so the alarm chain must be tested by bypassing water without tripping the valve.
• Remote test valve — at the hydraulically most remote point, giving the flow of a single sprinkler. It proves the water path is open along the entire distribution run.

Tamper switches and position monitoring

In practice, tamper contacts go on: the main control valve set stop valve, each zone stop valve, sectional stop valves on the ring main, the pump suction and discharge stop valves, and the tank fill valve. All of them should appear as separate zones on the fire alarm panel, with an alarm generated within the first quarter turn towards closed. At annual maintenance the tamper contact is tested by hand — closing the valve slightly on purpose and confirming the signal reaches the panel.

Comparison with NFPA 13

NFPA 13 uses the term control valve assembly and requires the same components: indicating control valve, alarm valve (wet, dry, pre-action or deluge), main drain, alarm test connection and inspector's test connection. Some differences:

• NFPA 13 specifies the flow and orifice for the inspector's test connection more precisely; EN 12845 says "the flow of a single sprinkler" and takes the size from the remote test valve type.
• NFPA 13 lists the acceptable indicating valves explicitly: OS&Y gate, indicating butterfly, post indicator valve and wall PIV. EN 12845 says only that the position must be clearly indicated, leaving the rest to the manufacturer and certification body.
• NFPA 13 sizes the main drain from a table by pipe size; EN 12845 sizes it by hazard class. The two approaches usually meet at DN50.
• NFPA defines a 60 second limit on alarm delay; EN 12845 describes the retard chamber but gives no specific time, leaving it to the manufacturer's approval report.

The five most common field errors

1. The "dead installation" — a half-shut stop valve. An unmonitored butterfly with the locking chain in the wrong position. The fix: monitor every main and zone stop valve and test the tamper signal at the panel.
2. A blocked or hidden drain outlet. The plug has not been removed since installation and the outlet is full of silt. You discover it when the main drain test shows flow down by half.
3. Supply and installation gauges swapped. If the upper gauge reads supply pressure, the installation is reversed and you cannot interpret the clapper loss. Know the riser schematic by heart.
4. Missing detection integration on a pre-action panel. The pre-action valve is fitted but the detector loop is not wired to the panel, so the valve trips only on manual release. An end-to-end test at commissioning is essential.
5. A wet alarm valve in a freezing area. The valve room is uninsulated or unheated. The feed pipe and control valve set must be kept at a minimum of 4 °C; if that cannot be achieved, either heat the valve room or move to a dry or alternate set.

Turkish context

BYKHY ties sprinkler installations to TS EN 12845. In practice, fire brigade and insurance inspections look for an EN 12259-2/3 certified control valve set, working gauges, drain and alarm test lines, and every stop valve wired to the fire alarm panel through a tamper switch. On industrial projects, FM Global approved sets are accepted directly; on conventional projects an EN 12259 approval is sufficient. At commissioning, the main drain test, the alarm test valve test (gong and pressure switch) and the remote test valve test must be recorded in writing; insurers may ask for those records later.

One point deserves repeating: the control valve set is both the heart of the system and its panic door. It is what lets water through when there is a fire, and it is what can leave a building unprotected during maintenance. That is why every sub-clause is written around safety — there is no line item in the set design you can wave through as a small detail.

Frequently Asked Questions

Why must the stop valve be monitored?

So that a half-shut valve cannot go unnoticed. A tamper switch signals within the first quarter turn towards closed, and that signal must reach the fire alarm panel.

What is a retard chamber for?

It absorbs brief pressure drops from pump fluctuation so they do not raise a false alarm, while passing the continuous flow of a genuine sprinkler operation.

How large must the main drain be?

40 mm on an LH installation and 50 mm on OH, HHP and HHS installations, with smaller sizes for trapped pipework.

What is the main drain test?

Opening the drain fully and reading the flow together with the drop on the supply gauge — the simplest check that the water supply still delivers its expected capacity.

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