For what purpose is the 3/32" hole in the clapper of the check valve?

The hole in the clapper of the check valve serves to allow air to enter the system while preventing water from escaping, making it essential for maintaining proper function within the piping system. Specifically, this small opening ensures that when the valve closes, the water pressure does not create a vacuum that could damage the system or impede operation. By allowing air to flow in, it helps in equalizing the pressure on either side of the clapper.

This functionality is vital for preventing potential issues like water hammer or backflow that could compromise system integrity. It also assists in reducing the likelihood of any unwanted siphoning effect that might occur in a closed system.

Other options do not accurately represent the purpose of the hole: adjusting pressure, providing a drain, or preventing evaporation are functions that are either unrelated to the check valve's primary role or handled by other components in the sprinkler system.