Auto Fill / Back Flow weirdness

[atxjmy512]

I’ve had my Auto fill off for a few weeks, preferring to fill by hose to ensure my water softener registers the flow. I've turned it back on to help me keep up. When I did so the back flow began discharging rhythmically from the backflow preventer (see video below).

It has since stopped but trying to figure out why this happened so I can address if necessary.

My pool is a flooded system so there is always some amount of pressure from the pool water pressing back on the backflow preventer. Maybe this was my autofill fighting that pressure as the pool pushed back?

Video

 

[atxjmy512]

Now that I think about it…. I hadn’t opened corky valve at the pool end. It was still below water level so it was closed. Not sure if that matters. But maybe influx of pressure from the water line combined with closed corky gave the water no where to go but out the backflow?

Now that I think about it #2…. I recently had my homes PRV replaced as my pressure was too high (90 - 100 psi). The last time I had my Autofill turned on was before that work was done, so theoretically the pressure in that line was in excess of what would have been coming out water line when I turned it back on. Maybe this was the the equalizing of that pressure.

 

[atxjmy512]

Still hasn’t happened like this again but I can briefly replicate it by opening and shutting the hose faucet that the autofill is connected to. It it's almost like when I shut the valve so quickly, the water flow diverts to the auto fill line and then purges through the backflow preventer. It's very brief and much less severe, just brief spray. I've also confirmed this by isolating the hose faucet by turning off the 1/4 turn valve on the pool end of the backflow prevent - the discharge still happens...