Douglas Krantz - Technical Writer - Describing How It Works
Go to the Fire Alarm Home Page of Douglas Krantz -- Describing How It Works
Go to the Fire Alarm Operation Map Page of Douglas Krantz - Technical Writer
Go to the General Electrical Map Page of Douglas Krantz - Technical Writer
Go to the Fire Alarm Description Map Page of Douglas Krantz - Technical Writer
Go to the Fire Alarm Installing Map Page of Douglas Krantz - Technical Writer
Go to the Fire Alarm Maintaining Map Page of Douglas Krantz - Technical Writer
Go to the Fire Alarm Testing Map Page of Douglas Krantz - Technical Writer
Go to the Fire Suppression Map Page of Douglas Krantz - Technical Writer
Go to the Science Article Map Page of Douglas Krantz - Technical Writer
Go to the Writer Home Page of Douglas Krantz -- Describing How It Works

Fire Suppression

Sprinkler Systems, when they're serviced, are often drained of water. When this happens, air replaces the water. When the sprinkler line is flooded again after servicing, the air gets compressed and often is not bled out of the system. This compressed air makes up air bubbles.
Sprinkler systems are long tanks. When water is drained out, they are full of air. When flooded with water again, the air usually does not have anywhere to go and just gets compressed, making the sprinkler system a long compressed air tank.
Douglas Krantz -- Fire Alarm Engineering Technician, Electronic Designer, Electronic Technician, Writer






Why Are There Waterflow Alarms When No Water is Flowing?

By Douglas Krantz

Between building trades, there's a natural line of demarcation. Sprinkler pipe fitters don't like working on a fire alarm system; they evacuate buildings. Fire alarm technicians don't like working on a sprinkler system; they make messes.

Building maintenance personnel don't always understand this line of demarcation, but when things go wrong, they do the best they can to figure out who to call.

False Waterflow Alarms

When the fire department arrives and the sprinkler system appears normal, but the fire alarm system keeps going into false waterflow alarms, it's natural to call the fire alarm company to fix whatever problems are causing the false alarms. At issue here, however, is that often times the cause of false waterflow alarms is really air bubbles trapped in the sprinkler pipes.

Air Entering the Sprinkler System

Any time the sprinkler system is drained by the sprinkler company for maintenance, air fills up the pipes in the sprinkler system. Once the maintenance is finished, water is let in back to fill the pipes. The air, which is trapped inside the pipe, gets compressed.

Whereas the air will slowly bleed out of the pipes through microscopic cracks, this bleeding can take months. In the meantime, the compressed air is a problem.

Conflict Between a Real Fire and Compressed Air

Normally, when a sprinkler head is heated by a fire, a link melts to allow water to spray out. At this point, water pushes past the flow switch.

When the city water pressure bumps higher (sometimes on a daily basis), and there's air bubbles in the pipes, water pushes past the flow switch to further compress trapped air.

Now, a flow switch cannot tell the difference between water flowing to a sprinkler head because of a fire, and water flowing to compress air bubbles. All it can tell is that water is flowing.

Conflict with the Air Bubbles

This temporary waterflow problem with trapped air is recognized, and is partially dealt with. To prevent the switch from activating because of trapped air, there's a retarder (damper) to delay the switch action. This delay is often :45 seconds. But too much trapped air and this delay may not be long enough to prevent false alarms.

However, there's another consideration to delay length. Because fires spread fast, and the alarm needs to be sounded quickly, most fire marshals don't want this delay to be longer than :45 seconds.

When there's too much trapped air, this all becomes a false alarm conflict.

The Fire Alarm Technician Arrives on Site

When it's the fire alarm technician that's called first, on arrival full diligence is needed. Remember, the fire alarm technician has to give the building owners an effort because, after finishing, the fire alarm technician is still going to "hold-out-the-hand" for payment.

Was this
helpful?
Yes   No

Ask about recent sprinkler maintenance history. If the system had been drained and refilled recently, that might lend a clue. But check out the fire alarm system anyway. Look for intermittent shorts, broken or loose switches, lose or broken connections, and fire alarm panel troubles.

Finally, if no fire alarm issues can be found, the best a fire alarm technician can do is explain the compressed air bubble troubles to the building's representative so the explanation can be passed on to the sprinkler company, and then leave.








Advertisement


Douglas Krantz

Describing How It Works
writer@douglaskrantz.com
Text
612/986-4210

View Douglas Krantz's profile on LinkedIn



Ask
The
Technician

Readers Questions



Short Circuit
Free Subscription
I'll Send You the
Twice-Monthly
Fire Alarm
Newsletter

Get Short Circuit


Articles

How Does Class A Fire Alarm Wiring Work?-- Fire alarm systems save lives and protect property. Fire alarm systems also break down because... Read More

Just What Is a Signaling Line Circuit (SLC)? -- The SLC (Signaling Line Circuit) is another way of saying Data and Power Circuit. Along with added power to run the sub-computers and their input and output circuits, it's a computer data-buss ... Read More

How is a Buffer Relay Wired Into a Door Holder Circuit? -- Like a door stop, a door holder keeps a fire door open. When smoke is detected, the door holder releases, allowing the door to shut. The door holder looks simple and innocuous enough... Read More

How Does One Find a Soft Ground Fault? -- Normally, we think of resistance like that of a resistor. The amount of resistance is built-in; no matter what voltage is used to drive the electrical... Read More

Can a Magnet Really be Used to Test a Smoke Detector? -- Smoke detectors usually have two ways of being tested. Smoke (smoke particles in the air, or some sort of canned smoke), and magnets (the activation of an internal magnetic... Read More



Electrical Flow


On this website, most references to electrical flow are to the movement of electrons.

Here, electron movement is generally used because it is the electrons that are actually moving. To explain the effects of magnetic forces, the movement of electrons is best.

Conventional current flow, positive charges that appear to be moving in the circuit, will be specified when it is used. The positive electrical forces are not actually moving -- as the electrons are coming and going on an atom, the electrical forces are just loosing or gaining strength. The forces appear to be moving from one atom to the next, but the percieved movement is actually just a result of electron movement. This perceived movement is traveling at a consistent speed, usually around two-thirds the speed of light. To explain the effects of electrostatic forces, the movement of positive charges (conventional current) is best.

See the explanation on which way electricity flows at www.douglaskrantz.com/
ElecElectricalFlow.html
.