We have anti syphon bottle traps on our bathroom basin wastes. One of them has started to make a noise that sounds like air being sucked in. Do these valves need maintenance and is there a diagram on the web that shows how they are constructed?
They are meant to suck in air through a small valve on the sewer side, to prevent water being sucked from the trap.
If this becomes crudded up or perhaps parts are worn, then it may make a sound doing so.
I have never seen spares for them, nor seen one where the antisyphon valve can be dismantled without breaking it.
If it is causing a problem, then these days I would replace it with a HepVO trap. These have a collapsing tube seal inside and no water trap. If there is a negative pressure on the drain side, air will be sucked through, but quite quietly.
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