Rachio's "Minimize Water Hammer" setting allows your controller to help with regulating the pressure surge that can be caused when a zone is abruptly shut, and subsequently diverted to a different zone. With this setting, your Rachio Smart Sprinkler Controller will open the 'next' scheduled zone to run in a watering schedule 10 seconds prior to the end time of the current zone that is running, in order to smoothly transition between zones and stop the knocking noise in your pipes.
How to activate Water Hammer
Go to the 'More' tab on your Rachio app.
Select the 'Controller Settings' option.
Scroll down and enable the 'Water Hammer' switch.