Where is residual pressure typically measured in a hydrant operation?

• A. Near a flowing hydrant
• B. At the hydrant valve stem
• C. At the discharge gate
• D. In the water tank

Answer: (A)

Residual pressure is the pressure left in the water system after water starts flowing. In hydrant operations you check it at the point where water is actually flowing—the hydrant you’re using—so you see the true mainline pressure under fire flow. This reflects the losses through the hydrant, piping, and any valves during that flow. Checking at the valve stem, the discharge gate, or in the tank wouldn’t show the actual pressure available in the distribution main during active flow—the values there are affected by local restrictions or storage and wouldn’t represent the system’s remaining pressure. Therefore, residual pressure is typically measured near a flowing hydrant.