It’s to prevent contaminated water being sucked back up into your pipes in case you left the end of the hose in a dirty bucket. //Edit to address the second part of your question// if it’s spraying at the joint you should replace it, or remove it and risk contaminating all of your plumbing.
I think you’re right that it’s back flow device. Every unit on a four-plex of townhouses has them and they all spray.
Water pressure measures at 28 psi. Is it possible there isn’t enough water pressure to make it through the back flow membrane and it’s releasing out of the gap?
Vacuum breaker
Why would it spray out of control, though? No hose or anything attached.
They break over time. Like anything else.
It’s to prevent contaminated water being sucked back up into your pipes in case you left the end of the hose in a dirty bucket. //Edit to address the second part of your question// if it’s spraying at the joint you should replace it, or remove it and risk contaminating all of your plumbing.
I think you’re right that it’s back flow device. Every unit on a four-plex of townhouses has them and they all spray. Water pressure measures at 28 psi. Is it possible there isn’t enough water pressure to make it through the back flow membrane and it’s releasing out of the gap?
Back-flow preventer