anti-siphon traps

[Fred]

Hello,

Has anyone tried the anti-siphon traps from Screwfix and do they work?

In our bathroom, the builders joined the basin and bath waste with a tee, so when the bath empties the basin "burps".

I know two separate wastes would fix this but in their wisdom the builders hid the soil stack in the wall and I would have to take half the bathroom and half the kitchen apart to get to it!

I have fitted such a trap to the basin but it still burps!

From the outside it looks like a normal trap. How is it supposed to work?

Thanks,

[John]

Not used the ones from Screwfix but the ones I have used, bought from various places, all worked. The one on the Screwfix web doesn't look like an anti-vac waste to me but that may be down to picture error rather than it being the wrong product. An anti-vac waste should have a 'hat' on top of the outlet pipe this is where the air is drawn in if it is needed. Have a look on

and search part no 15509 for a picture (third item down).

HTH

John

[John Stumbles]

You could try a Hepworth non-return valve type of trap on the basin waste.

[Fred]

No, it's not a picture error, it does not have a "hat" like the ones of BES.

[Doctor Drivel]

Which is also an air admittance valve too.

Called a HepVO trap. BES No. 15121.

Sometimes these anti-siphon and AAV traps may have to be fitted to basin and bath to stop the burping.

[meow2222]

If you unscrew the trap bit you'll see an extra tube inside to let air bubble through while making less noise.

NT

[Fred]

I did unscrew it and I did see that but (1) it doesn't work in my case and (2) why should the air want to move down a tiny little pipe rather than the big one?

[meow2222]

all good questions :)

NT

[Andrew Gabriel]

It would help if you identified exactly which product. I've fitted a bottle trap with air admitance valve, and that works extremely well. The pictures I can see on the screwfix website of the anti-siphon traps look like regular traps, at least, they're missing the air admitance valve that's on mine, but mine didn't come from screwfix.

[Fred]

[...]

Sorry for the delay in replying. It is the one that you saw on their web site already, like you say, without an obvious valve.

I'm not sure how to quote the url without the session id included, but they are part numbers 15739 and 19709 for 32 and 40mm respectively.