Anyone know much about anti-vac traps?

[Deleted member 120897]

So I thought I had a blockage in the whb as water was slow to drain, so used a cleaning brush down the plug hole earlier and no water would go down at all! Scooped all the water out and proceeded with normal unblocking methods to no avail. Although plunger was giving no resistance. Removed trap, snaked waste, put back together blocked straight away! Thought I would loosen the anti-vac part a little and the best it has ever flowed. Any thoughts please as I’ve only ever dealt with p-traps.

 

[ShaunCorbs]

Where did the basin exit / drain to a gully ?

 

[snowhead]

It's partially / fully blocked downstream of the trap.
The anti vac, which normally allows air in, is allowing the air trapped between the blockage and the plug of water out, letting the water drop down to the blockage.
Run enough water down and the flow will overcome what the blcokage will allow through.

 

[Deleted member 120897]

Where did the basin exit / drain to a gully ?

Soil and vent pipe externally and the whb waste; it runs under chipboard flooring.

 

[Deleted member 120897]

It's partially / fully blocked downstream of the trap.
The anti vac, which normally allows air in, is allowing the air trapped between the blockage and the plug of water out, letting the water drop down to the blockage.
Run enough water down and the flow will overcome what the blcokage will allow through.

So it can’t be a faulty anti vac part of the trap? Has copious amounts of water down now, it’s not a long run and no blockages as yet now.

 

[Deleted member 120897]

Oddly, I’ve screwed the anti vac part down again today and all flowing ok. Might have dislodged from loads of water.