Fire alarm tamper switch and flow switch: how your sprinklers report to the panel

A fire alarm tamper switch is a small switch fitted to a valve on your sprinkler system. It tells the fire alarm panel when that valve is moved away from fully open. The flow switch, which works alongside it, tells the panel when water starts moving through the sprinkler pipe. Together, they send the sprinkler system's signals to your fire alarm panel. This is what each one does, how they are tested, and how long they last.

What a fire sprinkler tamper switch does

The valves that control the water to your sprinklers are meant to stay fully open. A tamper switch is usually mounted on each of those valves to watch its position. If someone starts to close the valve, the switch sends a signal to the fire alarm panel. On the common type, the signal stays until the valve is fully open again.

On a valve opened and closed with a large wheel, makers set the switch to signal within the first two turns of the wheel. The common type also sends a signal if it is taken off the valve, and some have a second switch that signals when the cover is removed. Other valves, like the post outside the building that controls the water coming in, use a different style of switch that does the same job.

The tamper switch is how you know a valve was left closed after a repair, which is one of the most serious problems a sprinkler system can have. Our article on a closed sprinkler control valve covers how valves end up closed.

What a fire sprinkler flow switch does

A flow switch sits in the sprinkler pipe with a thin paddle inside it. When a sprinkler opens and water starts moving, the water pushes the paddle and the switch sends an alarm signal to the panel. It is meant to react to water flowing from a single sprinkler.

A short delay is built in, so a brief surge of pressure in the water supply does not set off a false alarm. The technician sets that delay as short as it can be while still preventing false alarms.

The difference between a supervisory signal and an alarm signal

The two switches send different signals, and the fire code requires them to be different.

• Water moving. A sprinkler may have opened, so the flow switch sends an alarm signal. Where the building has a fire alarm system, it sets off the building alarm, and the sprinkler system's own alarm on the outside of the building sounds too.
• A valve moved. A valve moved away from fully open does not on its own mean there is a fire. The tamper switch sends a supervisory signal: a notice that something on the sprinkler system should be checked.

Both go automatically to a monitoring center or, where the authority having jurisdiction approves, to an alarm at a place in the building where someone is always present.

Which valves must have a tamper switch

In New Jersey, the fire code requires the valves that control the water supply to an automatic sprinkler system, and the flow switches, to be watched electrically by the fire alarm control panel. There are exceptions, such as sprinkler systems in one- and two-family homes, and a few specific valves, such as the small valves on dry and pre-action systems, that can be locked or sealed open instead. Which of your valves have to have a switch depends on your systems and the code your authority having jurisdiction enforces.

How tamper and flow switches are tested

• Flow switch. The test valve on the sprinkler system is opened to let water flow, and we confirm the alarm signal arrives at the panel.
• Tamper switch. The valve is turned toward closed, and we confirm the panel shows the supervisory signal within the first two turns. Then the valve is opened fully and we confirm the signal clears.

A flow switch test can set off the building alarm, so tests are arranged with you ahead of time. How often each test is done is set for your system on our fire protection inspection calendar.

How long a tamper switch lasts

One maker puts the normal service life of its tamper switches at 10 to 15 years, and says it can be shorter where conditions are hard on them.

What we find most often

Many of the tamper and flow switch findings in our record are switches that did not work when they were tested, or that needed replacing.

We test, repair and replace tamper and flow switches across New Jersey, Pennsylvania and Delaware as part of our commercial fire sprinkler system inspections, and connect them to fire alarm monitoring where they are not yet watched. Send us a list of your sprinkler systems and we'll set up the switch tests on your inspection schedule.