Fire hydrants drain using a clever mechanism designed primarily to prevent internal freezing during cold weather.
The Drainage Mechanism Explained
The key to a fire hydrant's drainage lies in an underground valve linked directly to the main water supply valve.
- Main Valve Closure: When firefighters are finished using a hydrant and close the main water supply valve completely, a secondary mechanism is triggered.
- Drain Valve Activation: According to the provided information, "A drain valve underground opens when the water valve is completely closed". This drain valve is typically located at the base of the hydrant, below the frost line.
- Water Drainage: This opening allows any water remaining in the hydrant's vertical pipe and body to drain out into the surrounding soil or a gravel pit.
- Preventing Freezing: "this allows all water to drain from the hydrant body to prevent the hydrant from freezing." Removing the standing water eliminates the risk of ice formation, which could damage the hydrant or make it unusable.
Why Drainage is Crucial
Proper drainage is vital for the reliable operation and longevity of fire hydrants, especially in climates where temperatures drop below freezing. Without drainage, frozen water could:
- Expand and crack the hydrant's casing or internal components.
- Block the flow of water, rendering the hydrant useless in an emergency.
- Damage the main water supply connection underground.
Variations in Warm Climates
While the underground drain valve is standard in areas susceptible to freezing, hydrants in warm regions may differ. The reference notes, "In warm areas, above-ground hydrants may be used with one or more valves in the above-ground portion." In these cases, the risk of freezing is minimal, and the drainage mechanism may be different or less critical.
Summary of Drainage Process
| Step | Action | Result | Purpose |
|---|---|---|---|
| 1. Usage Ends | Firefighters close main water valve. | Water flow stops. | Ends water supply. |
| 2. Valve Closed | Main water valve is completely closed. | Underground drain valve automatically opens. | Activates drainage. |
| 3. Water Drains | Remaining water exits through drain valve. | Hydrant body and pipe are emptied. | Removes standing water. |
| 4. Freeze Prevention | Hydrant is empty below ground level. | No water to freeze. | Protects hydrant from ice damage/blockage. |
By utilizing an underground drain valve that activates automatically upon complete closure of the main valve, fire hydrants efficiently clear themselves of water, ensuring they remain functional year-round.
