When flushing fire hydrants, the pressure in the mains should not drop below what level?

When flushing fire hydrants, maintaining a minimum pressure in the mains is crucial to ensure that the water distribution system operates effectively and safely. A drop below the threshold causes several issues, including the potential for water quality degradation and inadequate water supply for firefighting efforts.

A minimum of 20 psi is considered necessary to prevent negative impacts on the system. This level helps avoid back siphonage, which could pull contaminants into the system if pressure is too low. It also ensures that sufficient water flow is available for fire protection and that the distribution system remains stable during maintenance activities.

While other pressure thresholds such as 10 psi, 30 psi, and 40 psi might seem valid, they either do not provide a balanced approach to system integrity or may exceed what is necessary for safe flushing practices. Thus, the 20 psi benchmark serves as the standard in many guidelines, reflecting a balance between operational safety and practicality during hydrant flushing.