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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