# Backflow preventer issue



## Ti837 (Aug 11, 2019)

I'm having an issue with my back flow preventer that I'm hoping someone can help me out with. I installed my sprinkler system last year. My main line to the house is 3/4" but I bought a 1" PVB (conbraco Apollo) because the poly pipe in ground is 1". The issue I'm having is when my sprinkler turns on I hear a click and water starts spewing out from the back flow preventer. It then takes about 30secs or so and the water will stop coming out from the cap and then the sprinkler system will start working properly. I have 9 zones in total and when I test out the system it's almost guaranteed that the back flow will trip and water starts coming out from the cap especially at zone 1. What do you guys think the issue is. Do you think it's because my main line is 3/4" but the back flow is 1"?


----------



## g-man (Jun 15, 2017)

The 3/4 to 1in should not matter. Do you have a valve before the PVB? Is the line after the PVB draining?


----------



## Ti837 (Aug 11, 2019)

what do you mean by is the line draining after PVB? I installed a shutoff valve inside the house


----------



## hsvtoolfool (Jul 23, 2018)

A Pressure Vacuum Breaker activates when the pressure on the irrigation-side is greater than the pressure on the supply-side. So my first guess is that the PVB is mounted lower than most of the heads/pipes in the system. This might create enough initial back-pressure to activate the PVB. My second guess is something is "open" on the supply-side of the PVB which drops the pressure initially. This is what g-man suggested with his _"valve before the PVB"_ question. Somebody may have "cheated" and tied a zone into the water supply _before_ the PVB. My third and final guess is that the PVB is busted.


----------

