What mechanism in hydrants prevents backflow of water into the main supply?

The mechanism in hydrants that prevents backflow of water into the main supply is a check valve. A check valve is designed to allow the flow of water in one direction while preventing reverse flow. This is critical in hydrant systems because it ensures that any water drawn from the hydrant, especially in emergency situations, does not flow back into the main water supply system. This is particularly important for maintaining the quality of the drinking water supply and preventing contamination.

In hydrant systems, the check valve automatically closes when the pressure in the hydrant drops below a certain level or when the flow direction reverses, effectively sealing off the connection to the main supply. This mechanism is vital for protecting the integrity of the entire water distribution system.

Other valve types, such as flow valves, regulating valves, and isolation valves, serve different purposes. Flow valves control the rate of flow, regulating valves adjust the pressure within the system, and isolation valves are used to stop flow from one section of the water system while maintenance is performed. However, none of these functions specifically address the prevention of backflow in the same manner as a check valve does.