Archives of Ask A Scientist!

About "Ask A Scientist!"

On September 17th, 1998 the Ithaca Journal ran its first "Ask A Scientist!" article in which Professor Neil Ashcroft , who was then the director of CCMR, answered the question "What is Jupiter made of?" Since then, we have received over 1,000 questions from students and adults from all over the world. Select questions are answered weekly and published in the Ithaca Journal and on our web site. "Ask A Scientist!" reaches more than 21,000 Central New York residents through the Ithaca Journal and countless others around the world throught the "Ask a Scientist!" web site.

Across disciplines and across the state, from Nobel Prize winning scientist David Lee to notable science education advocate Bill Nye, researchers and scientists have been called on to respond to these questions. For more than seven years, kids - and a few adults - have been submitting their queries to find out the answer to life's everyday questions.

Previous Week's Question Published: 7 November, 2002 Next Week's Question
How a Fire Hydrant Works
Question
How does a fire hydrant work?

Question
Fire hydrants are actually pretty simple in the way they work. Each fire hydrant is connected to a large underground pipe that carries water. To get water out of the hydrant, firefighters use a five-sided wrench to open up one or more of the covers and connect hoses to the openings, which are like the spigots on your faucets at home. Then, they use the same wrench to turn the 'stem nut', which is like your faucet's cold or hot water knobs. Water comes up through the pipe, through the openings, and into the hoses that lead to the fire engines.

The water that comes out of the hydrant is the same water that comes into homes, businesses, and schools. This water has a water pressure of about 50-80 psi (pounds per square inch). This pressure is high enough for everyday use, but is not high enough for use by firefighters. So, the pumps on the fire engines increase the pressure. Then, there are smaller hoses that attach to the engines that firefighters use to fight fires.

Fire hydrants in the cooler states have an added level of complexity because the temperature often goes below freezing in the winter. Since water expands when it freezes and turns to ice, the hydrant could crack if there is water in the hydrant when it freezes and expands. Also, if there was a fire during the freezing weather, the hydrants wouldn't work, because there would be a huge chuck of ice clogging the hydrant.

To avoid the problem of freezing water, many hydrants are 'dry barrel hydrants', which means that no water stays in the upper section of the hydrant when the hydrant valve is turned off. The valve that controls the water flow is below ground and there is a long rod that connects the stem nut to the valve. Next to the valve, there is a drain hole to let water drain out of the barrel of the hydrant after firefighters turn the valve off. The pipe that holds the water is buried deep enough so that it never freezes. (A bit of trivia: Because of this mechanism, it's near impossible for a car to run over a fire hydrant and cause it to gush water as they do in the movies, since there usually is no water in the upper part of the barrel.)