What action should be taken with the main drain valve after the system pressure stabilizes?

What action should be taken with the main drain valve after the system pressure stabilizes?

• A. Open it
• B. Close it
• C. Leave it closed
• D. Test for leaks

Answer: (A)

Purge the system to remove trapped air so the test reflects the true water-filled condition of the pipes. Opening the main drain valve after the pressure has stabilized allows any remaining air to escape and confirms the system is fully charged with water. If you kept it closed, air pockets could stay in the piping and skew readings or hide leaks. Testing for leaks comes after the purge and stabilization, but the immediate next step to ensure accurate results is to open the main drain to vent air.

Purge the system to remove trapped air so the test reflects the true water-filled condition of the pipes. Opening the main drain valve after the pressure has stabilized allows any remaining air to escape and confirms the system is fully charged with water. If you kept it closed, air pockets could stay in the piping and skew readings or hide leaks. Testing for leaks comes after the purge and stabilization, but the immediate next step to ensure accurate results is to open the main drain to vent air.