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Hello installers!

I’m looking into using anti-siphon vents for the first time indoors and I’m concerned about the likelihood of failure on the mechanical Auto-Vent (the spring can fail leading to leaks when the pump kicks in) and apparently they’re not allowed in many jurisdictions’ plumbing codes for this reason.

Other forum entry suggest they may last 10 years and to just replace them when they fail.  Fair enough, but I’m curious if a better alternative exists so I can instill confidence in my clients.

The alternative plumbers use is an Air Admittance Valve (which of course is more expensive) but I’m not finding any info about how these perform in a water pressure situation where they need to stop pumped greywater discharging from the washer. Apparently they reset when the negative pressure is gone

Any tests or experiences out there?




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I have used both the lower cost autovent as well as the air admittance valve and find them to work the same. I haven’t seen either fail, though of course that is a possibility, which is why they should be located in a visible location. (I have seem some come with a manufacturer defect and leak upon first use, but I’ve never seem them leak over time.) I would be comfortable using either type indoors, so long as you show the valve to your client/homeowner as well as include information about it in the O&M manual.

It is true that these are not allowed in many places to be used to vent a fixture. In the L2L system they are not acting as a vent, and are not venting any fixtures in the house. It is a mute point that they are not allowed as a vent, since they are not being used as a vent. Hope that makes sense! They are being used to break a siphon and are connected to an appliance, the washing machine. They are not even discussed in plumbing codes as an anti-siphon device, so any information about them from plumbing codes is not relevant to this application.

Hope this helps!

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