What will raise the fire main pressure?

Starting pumps is the correct answer because pumps are designed to increase the pressure of fluids in a system. In the context of a fire main, which is a crucial part of a fire protection system, initiating the pumps will actively circulate water at higher pressures. This is essential for delivering water to fire hoses or sprinkler systems effectively.

When pumps operate, they create a pressure differential that enhances the flow of water throughout the fire main. This is particularly important in emergency situations where quick access to high-pressure water is necessary for firefighting efforts.

The other options do not contribute to raising the fire main pressure. Closing valves typically restrict flow and can lower pressure in the system, while opening drains would allow water to escape, thus decreasing pressure. Shutting off supply would also restrict flow and diminish pressure, as it limits the amount of water available to the system.