Why should dry barrel hydrants be opened completely?

Opening dry barrel hydrants completely is crucial because it ensures the drain valve is fully closed. Dry barrel hydrants are designed to prevent water from sitting in the barrel when it is not in use, which helps prevent freezing in cold climates. When the hydrant is fully opened, the mechanism is designed to seal the drain valve effectively, preventing any excess water from leaking into the barrel area, which could lead to freezing and other operational issues.

While other options may touch on relevant aspects of water flow or leakage, the functionality of the dry barrel design is primarily concerned with maintaining proper drainage and preventing any chance of freezing. This is why the complete opening of the hydrant is essential for ensuring the drain valve is securely closed, which safeguards against the unwanted accumulation of water.