Tundish makes loud noise when draining bath water

[nmg196]

I have a bedroom air conditioning unit which drains water to the bath waste pipe via a tundish valve (this was my idea - not the A/C installers as I didn't want them to run a huge white pipe down the front of my house). It works perfectly for the purposes of the A/C to drain condensate but unfortunately if you drain the bath, the negative pressure causes the valve to make a very loud "whale noise" which would easily wake up our baby. Is there anything I can do to fix this?

If I replace it with a 23mm U-bend I'm worried it will eventually dry out when the A/C is not in use and then provide an open path from the soil stack to the bedroom A/C unit.

Here's a 10 second video showing the problem:

(it's not as loud as usual as I didn't fill the bath very deep for this demo).

Any ideas appreciated!

 

[Hugh Jaleak]

I'd swap that current assembly out for a 32mm HepVo Valve, should solve your issues. Bath draining is creating a vacuum in the pipework, which is in turn, pulling air through the Tundish, and possibly breaking the water seal anyway.

 

[nmg196]

I did consider that but I wondered if the same thing would happen and it would make the noise of letting air out of a balloon instead of the whale song noise The internal HepVo valve design actually looks like a Whoopie Cushion valve and there are reports of hepvo valves making farting noises already posted online!

Maybe I just need to somehow connect it "upstream" of the bath U bend (P trap) but it's incredibly difficult to access.

 

[Hugh Jaleak]

Given the volume and head of water likely to be present when a bath filled to a half decent level gets let go, I suspect you'll have issues wherever you connect it to the bath drain. Any option to run a dedicated waste pipe from the A/C unit to the stack?

 

[Madrab]

As suggested, a separate run to the stack would be the sure fire way to remove your issue.

If that's not an option though then no reason not to add a trap and then put an aav on the top with a side inlet for the condensate and take away that one way valve. It takes an awful long time for a trap to dry out. Even then the AAV could be popped off and some water added if ever needed.

How long is the waste run to the downpipe (stack)?

You could also consider increasing the pipe to 50mm and fitting an antivac at the bath. It may help to reduce the pull on the condensate pipe.

 

[nmg196]

I recently refitted the bathroom and the soil stack is all tiled in. However I think I may be able to access the bath overflow's vertical pipe and T into that - which would then result in the AC draining to the 'safe' side of the bath's own P trap.

 

[Hugh Jaleak]

Just as a point of note, chances are the bath overflow will be Polypropylene, so you will need a compression overflow fitting to connect, it wont solvent weld if you weren't aware.