How to Replace an Anti-Flowback Valve Sprinkler

Turn off the building's irrigation system shut-off valve, located near the building's water meter. Turning the shut-off valve's handle counterclockwise closes the valve.

Locate the sprinkler system's anti-flowback valve. An anti-flowback valve with an anti-siphon device mounts to the sprinkler system above ground near the system's shut-off valve. An inline anti-flowback valve connects to the sprinkler system below ground, between the shut-off valve and the first sprinkler head.

Lift the lid off the valve access box, which covers an inline anti-flowback valve. The valve access box's lid rests flush with the ground's surface and often has an "Irrigation" label.

Place an adjustable wrench on the part of the anti-flowback valve's union fitting that connects to the sprinkler pipe. The union fitting connects to the valve's intake port. The arrow on the valve's housing points away from the intake port.

Set a second adjustable wrench on the union fitting's compression nut, which holds the union fitting together.

Hold the union fitting's sprinkler pipe connection still, using its adjustable wrench for leverage. Turn the union fitting's compression nut counterclockwise with the second adjustable wrench. Continue to turn the compression nut counterclockwise until the nut releases the pipe connection.

Grasp the sprinkler pipe that connects to the anti-flowback valve's discharge end with a pipe wrench. Place an adjustable wrench on the anti-flowback valve's discharge pipe fitting, the fitting where the arrow points.

Hold the sprinkler pipe still, using the pipe wrench for leverage, and turn the anti-flowback valve counterclockwise with its adjustable wrench. Remove the valve.

Remove the debris from the male fitting on the end of the sprinkler pipe that connects to the anti-flowback valve's discharge end, using a rag to wipe the debris from the male fitting's threads.

Cover the last three threads on the sprinkler pipe's male fitting with a pipe thread compound. Do not place pipe thread compound on the union fitting's threads.

Spin the new anti-flowback valve's discharge port clockwise onto the sprinkler pipe's male fitting. The arrow on the valve points at the discharge port. Hand tighten the valve.

Hold the sprinkler pipe still, using the pipe wrench for leverage. Turn the anti-flowback valve one full turn clockwise with adjustable wrench. If the anti-flowback valve uses an anti-siphon device, continue to turn the valve clockwise until the anti-siphon device faces upward.

Align the union fitting on the end of the sprinkler pipe with the anti-flowback's input port. Spin the anti-flowback valve's union nut clockwise and hand tighten the union nut.

Turn the union nut clockwise one full turn with an adjustable wrench, while keeping the union fitting's sprinkler pipe connection still with the second adjustable wrench.

Turn the irrigation system's shut-off valve's handle clockwise, turning on the water supply to the anti-flowback valve.