Spring Startup: Backflow Preventer Dumping Water When System Pressurized

On spring startup, water flushes from the piping near the turn-on point instead of going through the lines. The user adjusted small screws but water continues to flow out an opening rather than through the system.

The Backflow Preventer Sequence

Matt diagnoses: "It sounds as if your backflow preventer is what is dumping the water." His procedure:

1. Close the valve going to the sprinkler system (downstream valve).
2. Leave the house supply valve (upstream) open.
3. Turn on the water.
4. If dumping stops, slowly open the downstream valve to let the backflow preventer pressurize gradually.

This allows the backflow preventer's internal check valves to seat properly against the rising pressure. Rapid pressurization can cause them to stay open and dump water through the relief port. This is a standard spring-startup procedure for systems with backflow preventers.