What should be open to perform a main drain test correctly?

To perform a main drain test correctly, it is essential to have the alarm control valve open. The main drain test is used to evaluate the flow rate and verify that the system can adequately supply water in the event of an alarm condition. By opening the alarm control valve, you ensure that the system can properly discharge water while checking for flow and assuring that the alarm system functions as intended. This step is critical because it simulates a fire scenario, allowing the system to operate under load and confirm whether the water supply can reach all necessary areas of the designed system.

In contrast, although other valves are important for various functions within a water-based system, they do not directly contribute to performing the main drain test itself. The main drain valve is essential for draining purposes but does not provide the necessary operational flow during a test. The flow control valve regulates the amount of water flowing through the system but isn't the primary opening that allows for the testing process during this procedure. Lastly, the water supply valve, while crucial for providing water to the entire system, is typically kept open to ensure flow but isn't specifically manipulated during the main drain test.