How Does a Dry Sprinkler System Work?
A dry sprinkler system is much like a wet sprinkler system, but inside the pipes is pressurized air instead of water that can freeze. When there's a fire, air leaves the system to let water come in to help fight the fire.
The Dry Sprinkler System Valve is in blue on the right
By Douglas Krantz
When a fire starts burning in a building, action needs to be taken early... before the fire has grown out of control.
Taking this action, sometimes before anyone even knows about the fire, is the Automatic Sprinkler System. Heat from the fire activates a sprinkler head, and water, now spraying from the activated head, suppresses the growth of the fire.
What is a Dry Sprinkler System?
A wet sprinkler system has water in the pipes. A dry sprinkler system, even though it will spray water on a fire, has no water in the pipes; only pressurized air.
Why Install a Dry System?
In northern climates during the winter, inside attics and garages, water in the pipes
of a wet sprinkler system will freeze and break the pipes. Lots of mess.
The water can't be in the pipes where it can freeze, but water is needed in a fire sprinkler system for spraying on a fire. This is a dilemma.
To solve the dilemma, instead of the water in the pipes of a wet sprinkler system
, the dry sprinkler system keeps pressurized air inside the pipes, and the air doesn't freeze.
To keep the water out, like a dam on a river, a clapper valve is used to divide the wet pipes from the dry pipes. Holding back the water, pressurized air inside the dry sprinkler system pushes against the clapper, keeping the clapper closed.
Heat Lets the Air Out
When the heat from a fire melts a link on a sprinkler head, the sprinkler head opens and lets the air out.
Water Fills the Pipes
By itself, of course, this doesn't do anything, but once the air is let out
, there's nothing to hold the clapper closed, and water rushes into the dry system like a dam bursting. The dry sprinkler system has become a wet system.
At this point, like a firefighter with a hose, the water sprays out and quenches the fire.
When heat melts the link in a sprinkler head, because as far as the dry sprinkler system is concerned it's suppressing a real fire, the building fire alarm system
is going to sound off and call the fire department.
Dry Sprinkler Fire Suppression System
Being ready to spray water on a fire, a dry sprinkler system will suppress a fire, even though, until heat from a fire activates one of the sprinkler heads, the pipes are filled with pressurized air.
Based on his electronics training, and his understanding of Life Safety, Douglas Krantz has compiled his knowledge of Conventional Fire Alarm Systems into the book Make It Work - Conventional Fire Alarms
. The book covers the basics of the Conventional Fire Alarm System, and shows how Life Safety and internal supervision affects the fire alarm system.
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