Faulty Anti-Drain Check Valve
Zone 3 · Head continues spraying after zone shuts off
What I Found
Symptom
Head continues spraying after zone shuts off
Confirmed Cause
Failed anti-drain check valve in spray body
Zone Affected
Zone 3 (front lawn, east bed)
James's Observation
The water draining from your lowest-elevation head after every cycle is the giveaway. This is a classic check valve failure — it has nothing to do with your zone valve or controller. I can rule both of those out from what you’ve shown me.
Why I Reached This Conclusion
Anti-drain check valves hold water in the line after shutoff, preventing low-elevation heads from draining. When the valve fails, the head at the lowest point acts as a drain for the entire zone. The pattern in your video is consistent with this failure and no other common cause.
- Water drains from one specific head — consistent with a lowest-elevation drain pattern
- Zone pressure appears normal on other heads (rules out pressure issue)
- Shutoff is clean at the valve box (rules out zone valve failure)
- Symptom began gradually, not suddenly — consistent with check valve wear
Alternative Causes I Ruled Out
- Zone valve failure — shutoff was clean at the valve box
- Broken lateral line — no visible wet spots or uneven pressure across the zone
- Faulty solenoid — zone activates and runs normally, only the drain pattern is wrong
Each of these was considered and eliminated based on the photos and video you submitted. The evidence points clearly to one cause. When the pattern is this specific, there is no need to guess.
Recommended Part
Part
Hunter Pro-Spray PRS40 with Integrated Check Valve
Part no. PS-04-PRS40-CV
Approximate Cost
$12–$16
Available At
Home Depot, Amazon, or local irrigation supply
James's Note
Replace the entire spray body, not just the check valve insert. It takes the same amount of time and the integrated PRS40 adds pressure regulation, which protects your nozzles long-term. This is what I’d put in my own system.
Repair Assessment
Difficulty
Easy
Time
10–15 minutes
Tools
Flathead screwdriver
- Shut off your irrigation controller
- Unscrew the existing spray body by hand (counterclockwise)
- Thread in the new PRS40 body — hand-tight plus a half turn
- Reattach the original nozzle
- Run Zone 3 for a full cycle and confirm the head stops after shutoff
Before You Finish
- If the head still drains after replacing the body, check whether another head on the same zone sits at a lower elevation — you may need to replace both.
- If you see cracking in the body threads when removing the old head, the riser pipe below may also need replacing. This is a simple addition to the same repair.
James's Recommendation
“Based on what I reviewed, this is a straightforward repair. You don’t need a contractor for this. Buy the Hunter PRS40, replace the body, and you’re done. If anything looks different when you pull the old body out, send me a photo.”
— James Caldwell, Licensed Irrigation Technician
Your Repair Plan
Problem
Failed anti-drain check valve in spray body
Recommended Part
Hunter Pro-Spray PRS40 with Integrated Check Valve
Estimated Cost
$12–$16
Difficulty
Easy
Repair Time
10–15 minutes
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