Master valve and Water Hammer

Has anything changed with the way the master valve operates on Gen 2?

Here’s the situation: Ran all last season with Gen 1 and everything worked beautifully. This season, however, I upgraded to Gen 2 controllers and now have a horrible water hammer problem, even with the Water Hammer setting enabled (and I use a Flex schedule). Other point to note is that the irrigation water branches off our incoming main before a pressure regulator that helps restricts house pressure (to ~50 PSI). Here are my questions:

  • When the water hammer setting is not enabled, as the Rachio switches from zone to zone does it open and close the master valve, or is it “smart” and leaves the master valve open? In other words, leave the master valve open until the entire schedule is complete and just open/shut the zone valves?

  • When a zone finishes running, does Rachio shut the master valve and the zone valve at the same time? Or does it shut one before the other? Would that help the hammer?

  • One of the suggestions I’ve seen online is to order the zones from highest to lowest volume. Has anyone tried this and found that it works?


Thanks for the questions. I’m having @Devin our hardware guru do some research and will get back with answers.


Hey stonecliff,

I can answer a few of these questions.

  1. The Controller opens and closes the Master Valve once per schedule. A note is that if you have Smart Cycle enabled, it will close the Master Valve while it’s soaking.
  2. When a Schedule finishes the Controller shuts off the Zone Valve first, waits 1/4 a second, and then turns off the Master Valve.

Water Hammer prevention works by turning on a Zone before its “official” start time. A quick test that this is happening for you would be to create a Schedule with 2 Zones in it and then manually run the Schedule. You should see both Zones running at the same time when the Schedule is transitioning from the first Zone to the second.

Unfortunately we can’t do anything about the water hammer from the first Zone starting.

I hope that clarifies a few things. Let us know what you find!



Many thanks for the info. Knowing how it works is helpful in diagnosing what is going on. It definitely happens when a valve closes, and helpful to know (1) that the master stays open for a schedule and (2) that it closes after the zone valve.

I’m still wrestling with whether the water hammer setting makes it better or worse in my case. Two zones open at once moves a lot of water at a time, and I wonder if I get less fluctuation going from “1 to 0” instead of “2 to 1”. Need to do some testing.


Thanks for the response. Happy that @Devin was able to shed some light for you. If you want to do some testing with regards to the water hammer and keep us posted that would be great. Interesting thinking on your end.

If you have any other questions don’t hesitate to let us know.

Thanks again,