Bucket Brigade, Fire Engine, Sprinkler System, Sprinkler Head, Fire Pump, Jockey Pump, Wet-Pipe and Dry-Pipe

Posted by PITHOCRATES - April 23rd, 2014

Technology 101

(Originally published March 20th, 2013)

A Fire Engine can move Water Faster and Farther with an Internal Combustion Engine than with a Steam Engine

Some of our earliest firefighters were bucket brigades.  Where people would form lines between a fire and a water source.  Someone would dip a bucket into the water source.  And then pass it to the next person in line.  Who would then pass it to the next person in line.  And so on until the bucket reached the person at the other end of the line.  Who then poured the water on the fire.  Then the empty buckets would work their way the other way back towards the water source.  Buckets of water moved from the source of water to the fire.  While empty buckets moved from the fire to the water source.

This was state of the art firefighting at the time.  As long as there were enough people to form a line from the water source to the fire.  The people didn’t tire out before the fire did.  And the fire wasn’t so large that buckets of water couldn’t put it out.  But soon we developed the hand-operated pump on our first fire engines.  And the fire hose.  Then we just had to run a fire hose from the water source to the fire engine.  And a fire hose from the fire engine to the fire.  People could take turns hand pumping, producing a steady stream of water.  That someone could direct onto a fire.  These new firefighting crews could put out large fires in shorter times.  Fire companies appeared in cities with trained firefighters.  Providing safer cities.  A great improvement over the bucket brigade.  But not as good as what came next.

Men pulled the early fire engines.  Then horses replaced men.  But the big advancement was in the fire pump.  When steam power replaced hand power.  Allowing greater flows of water at higher pressures.  Allowing firefighters to attack a fire from a safer distance.  But steam had some drawbacks.  It took time to boil water into steam.  Steam engines needed boiler operators to carefully operate the boiler so it didn’t explode.  And being an external combustion engine there were a lot of moving parts in the open.  That could be dangerous to the firefighters.  And being exposed to the elements they needed constant oiling.  The internal combustion engine didn’t suffer any of these drawbacks.  The modern fire engine is safer.  Easier to operate.  More efficient.  And can move more water faster and farther.

A Jockey Pump in a Sprinkler System maintains the Water Pressure when there’s no Fire

But even the modern fire engine has one drawback.  We park them at firehouses.  While all our fires are not at firehouses.  So they have to drive to the fire.  Which they can do pretty quickly.  But that’s still time a fire can grow.  Causing more damage.  Become stronger.   And more difficult to put out.  Which is why we brought fire-fighting water into buildings.  To use on a fire even before the fire department arrives on the scene.  Buildings today have fire sprinkler systems.  Pipes filled with water covering every square inch of a building.  That will release their water through the various sprinkler heads attached to these pipes.

The sprinkler head is a marvel of low-tech.  It is basically a threaded fitting that screws into the water-filled pipe.  The sprinkler head has a hole in it.  A glass bulb with a liquid inside of it holds a plug in the hole.  Preventing the flow of water.  If there is a fire under this head the heat will cause the liquid in the glass bulb to expand.  Eventually shattering the glass bulb.  The water pressure inside the pipe will blow out the plug.  Allowing the water to flow out of the pipe.  As it does it hits a deflector, producing a spray pattern that will evenly cover the area underneath the head.  Only areas where there is a fire will break these glass bulbs.  So only the sprinklers over fires will discharge their water.  Preventing water damage in areas where there is no fire.

Some buildings can operate off of city water pressure.  But larger buildings, especially multistory buildings, need help to maintain the water pressure in the system.  These buildings have fire pumps.  A large pump that can maintain the pressure in the sprinkler lines even if all the sprinkler heads are discharging water.  And a smaller jockey pump.  Which maintains the pressure in the system when there is no fire.  If the pressure drops below a lower limit the jockey pump comes on.  When the pressure rises above a higher limit the jockey pump shuts down.  If there is a fire in the building the fire pump will run until it melts down.  Putting water on the fire as long as it can.

A Dry-Pipe Fire Sprinkler System in an Unheated Area is often attached to a Wet-Pipe System in a Heated Area

If water would greatly damage an area (such as a hardwood basketball court) they may add a valve on the pipe feeding the sprinkler piping over the floor.  Keeping the water out of the pipes over the expensive hardwood floor.  Smoke detectors in the ceiling will open the valve when they detect a fire.  Letting water flow into the sprinkler lines over the floor.  And out of any sprinkler head over a fire hot enough to have broken the glass bulb to release the plug.

Water damage is a real concern.  For it may be a better alternative to fire damage.  But water damage in absence of any fire can be costly.  Something many have seen working on a new building in a northern climate.  During the first freeze.   If there was missed insulation on an exterior wall.  Under-designed heating in an exterior glass-enclosed stairwell.  Or both in a glass-enclosed vestibule that juts outside of a heated building.  As temperatures fall cold air migrates around these sprinkler lines.  Freezing the water inside.  Causing them to burst.  And when they do it releases the water pressure behind these frozen sections.  Flooding these areas with water.  Causing a lot of damage.  Not to mention the damage to the fire sprinkler system.

Some unheated areas need a sprinkler system.  But these pipes can’t be a wet-pipe system.  Because if there was water in the pipes it would freeze.  Breaking the pipes.  So we use a dry-pipe system in unheated areas.  Which is often attached a wet-pipe system.  Such as a dry-pipe system in an exterior canopy attached to a heated building.  There is a valve between the interior wet-pipe system and the exterior dry-pipe system.  An air compressor will put air under pressure in the dry-pipe system.  This air pressure will hold the valve close to the wet-pipe system.  If there is a fire underneath the canopy the glass bulb in a sprinkler head will expand and break.  Releasing the air from the dry-pipe system.  Allowing the water pressure in the wet-pipe system to open the valve.  Flooding the dry-pipe system.  And flowing out of the sprinkler head over the fire.



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