The fire hydrants are a common sight in cities, especially in shopping areas. They are a blessing to the firefighters. The hydrants help the firefighters access underground water through hoses. If there’s a fire anywhere, the firefighters will connect their hoses to the hydrant and fight the flames. However, we know that the water in our pipes can sometimes freeze if we have an especially cold winter. Fire hydrants, on the other hand, need to stay functional for our safety. How do the authorities manage to keep their water from freezing?
Most of these hydrants, as we see them today, have been around for about two centuries. Frederick Graff Sr., chief engineer of the Philadelphia Water Works, is credited with the invention of the current fire hydrants at the turn of 19th century. This design is known as the pillar or post type. He is said to have obtained the first patent for a hydrant, but it is unconfirmed as the United States patent office itself was decimated in a fire in 1836.
Hydrants are of two types: wet barrel hydrants and dry barrel hydrants. The one that was developed by Graff was the wet barrel kind which had the main valve on top of it. It had a constant flow of water into the hydrant. The problem with wet barrel hydrants is that they can be useful only in warmer climates. In the colder areas, the water tended to freeze up and be useless in case of any emergency. It is the dry barrel hydrant that is used in areas very much affected by cold.
In dry barrel hydrants, the water doesn’t always flow into the hydrant. Only a small part will be above the ground. This is used to connect the hose to the hydrant when necessary. These hydrants would have two valves: the main valve and the drain valve. Only one valve will be open at a time. The main valve allows water flow into the hydrant while the other helps to drain out the water into ground after the use. Unlike the wet barrel design, in which the main valve is above the hydrant, the valve connecting the hydrant to the water main is very much deep under the ground in dry barrel hydrants. The design doesn’t allow the water to remain in the hydrant. Since there is no water in the hydrant, there is nothing to freeze.
The water pipe and valve in dry barrel hydrants will be under the frost line, the maximum depth to which the ground freezes in winter. The part above the ground is a simple metallic pipe. Another advantage with the design is that even if an accident takes place, it doesn’t result in a leakage of water. However, dry barrel hydrants are not completely free from hazards. In unusually cold weather, the frost line can move much deeper and cause damage to the water pipes.
Dry barrel fire hydrants are designed to prevent the water freezing for as long as possible. However, there have been cases where this design has failed. This occurs when the drain valve or the main valve in side stop working or don’t function as well as they should. This is not the fault of the design itself, but a lack of proper maintenance or the natural wear and tear over time. It’s necessary to replace these valves over time, failing which the water might eventually freeze during winter.
At other times, even a dry barrel fire hydrant could fail due to an extremely cold winter season. This will move the frost line even further into the ground, causing issues within the water main. The phenomenon could potentially damage the hydrant’s valves. Such risks are why we might see crews testing fire hydrants before and during winter in order to make sure there wouldn’t be any problem with freezing.
Plus, firefighters will notify the relevant utility company after they’re used a dry barrel fire hydrant. The company will then come and ensure that the draining function is in place. They do this by dropping a weighted string into the barrel. If the string drops down completely, they know the water has drained out properly. If it doesn’t, it means that there’s some frozen water left behind.
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