How to operate
A Fire Hydrant
How Do Fire Hydrants Work?
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fire hydrants are all around us these
above-ground pipe fittings can supply
flows upwards of 1,500 gallons per
minute to save lives and put out fires
across the world we all know what fire
hydrants do but how exactly do they work
called fire plugs fire pumps Johnnie
pumps fire hydrants
these life-saving pipe fittings have
been around since 1801 their designs
vary by country of origin but they
usually have a connection point to hook
up a fire hose and a nut or bolt to turn
on what will start the flow essentially
every fire hydrant is just an attachment
to a main potable water line if you see
one on the side of the road there's
likely a potable water line running
underneath that connects the hydrant
valve through a pipe called a riser it's
important to note that normal hydrants
don't alter the pressure or flow of the
water in any way they simply function as
valves so firefighters can utilize the
already present pressure in the water
pipes while all of this may sound simple
the internal mechanics of a fire hydrant
are a little more complex and can vary
by region in the u.s. there are two
types of hydrants wet barrel hydrants or
dry barrel hydrants which we'll focus on
primarily in this video what barrel
hydrants are used where freezing
temperatures are uncommon in this design
water fills the entire hydrant at all
times in the valve to start the flow of
water is placed above ground this design
is usually cheaper to construct and
easier to maintain due to the majority
of its mechanism being easily accessible
dry barrel hydrants on the other hand
are used where temperatures routinely
drop below freezing and thus in order to
keep the water in the hydrant from
freezing the valve is placed below the
areas frost line the nut to turn the
valve on is usually placed on top of the
hydrant in this design to turn the long
valve running through the hydrant and
the riser these two hydrant designs
encompass the majority of fire hydrants
in the US and even many parts of the
world however their complexities and
intricacies don't stop there other
important aspects to note would be that
the flow of a hydrant isn't variable
during operation their valves are
designed to be totally open or totally
closed coupling this with the
that each hydrant is only a valve and
usually not a pump the output of the
water is solely dependent on the
pressure available to the hydrant at
that point in the water line the higher
the pressure the more water the hydrant
can output to stop a fire common flow
rates for hydrants across the u.s. range
from less than 500 gallons per minute
all the way up to above 1,500 gallons
per minute higher flow rate hydrants are
usually needed in commercial areas in
dense residential areas essentially
where there's potential for larger fires
the hydrants with the highest flow rate
deliver enough flow to fill a backyard
swimming pool in just three minutes in
the u.s. the colors of hydrants can also
indicate their type white means public
system hydrant yellow means it's
connected to a public water main red
means it's for use in special operations
and not for other use and violet means
non potable supply or water from an
untreated source like a lake some
hydrants are rarely used which is
obviously preferable but they still have
to remain at the ready this importance
means that the fire marshal and other
authorities perform regular inspections
of hydrants usually by attaching a
pressure gauge and measuring the flow of
water inspectors will check flow rate
valve functionality and pressure in the
pipe both before and during the flow
it's important that the pressure in the
surrounding pipes doesn't drop below 20
psi during hydrant flow if the pipe
pressure does this then certain areas of
the water network can drop to negative
pressures and suck in water from the
ground possibly containing microbes and
bacteria if you ever get a boil water
notice it's likely that some unforeseen
event like a flushing of a hydrant
caused pipes in your water system to
drop in pressure so these metal above
ground pipe fittings that often meet the
rear ends of man's best friend are
actually life-saving pieces of
engineering that have to remain at the
ready to supply water to firefighters on
the sides of roads across the country
and the world thanks for watching if you
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