When filling a water main, what should the water velocity not exceed?

When filling a water main, the water velocity should not exceed 1 foot per second to ensure that the system is filled gradually. This slow filling rate helps to prevent air entrapment and minimizes the potential for water hammer, which can occur if the water fills the main too quickly. Water hammer is a pressure surge that results from a sudden change in water flow, which can damage pipes, fittings, and joints.

Maintaining a low velocity during this process also ensures that any sediment or debris that may be present in the empty main can settle properly, thus reducing the likelihood of these contaminants being stirred up and entering the system. Furthermore, filling at a lower velocity allows for better monitoring and control of the filling process, reducing risks associated with leaks or overpressure.

Higher velocities, as suggested in the other options, could compromise the integrity and functionality of the water main, leading to problems such as increased turbulence and the risk of potential system failures. Therefore, adhering to the recommendation of not exceeding 1 foot per second is crucial for the safe and effective filling of water mains.