Shower Tray Not Draining

[It's me]

When I fitted our shower tray, I installed the waterless trap that came with it. Whilst it stops hair going down the drain, it is not very good at stopping noise from the other drains. When the downstairs toilet flushes or the washing machine empties, the noise is heard upstairs. With the old bath and u-bend, this did not happen.

To overcome this, I added a u-bend further along the drain. This stopped the noise, but also stopped the tray draining. To try and overcome this, I added an air admittance valve. This did not help either, but when I remove the valve and have just the open pipe, all is well.

Fig 1 shows the original plumbing.
Fig 2 shows with the extra AAV
Fig 3 shows what works

Does anyone have suggestions why the AAV did not help? Have I misunderstood their purpose?

James

 

[Wayners]

Can you run with AAV off then? Trap stopping smells and if it runs away fine leave as is.

 

[It's me]

Can you run with AAV off then? Trap stopping smells and if it runs away fine leave as is.

Hello, Wayne.

Yes, it does drain, which is how I have left it. However, I am just puzzled about the AAV and whether I was being unrealistic putting an AAV where I did. I had also hoped that it would help to stop the pipe overflowing if the pipe hbacks up for any reason.

 

[denso13]

Shower wastes can be slow running, perhaps not enough to open the AAV.

 

[DP]

Waterless trap has pressure build up tray side and is clear to the drain.
With additional trap, both sides of this valve have water so valve does not open.

It is same when you fill a tumbler to the brim with water, place a card on top of the full tumbler, invert it, take your hand away from the card. Water in the tumbler stay in the glass

 

[dilalio]

What @DP said, plus...

The water held in the running trap that you have installed creates more resistance than the water leaving the tray can overcome and displace.

The AAV allows air to be drawn in but not expelled out.

Removing this, as per your Fig.3, looks like it's allowing the vertical pipe, connected to it, to fill with water, this creates a "head" of water which is enough to overcome the resistance of the trap and displace it.

Is the right hand AAV able to be changed to a vent? This may overcome the issue or you could try replacing the running trap with a hepVO - which "may" stop the noise.

 

[It's me]

Thank you for your replies, which have really helped. Taking out the gubbins in the waterless trap in the tray enables the tray to drain with both valves in place. I would rather not replace the original AAV with a vent as it vents directly into the main drain. Without it, the downstairs toilet smelt in summer. The AAV solved that.

I shall leave both traps in, but leave the AAV off from the pipe on the shower tray side.

At least I now know why it didn't drain.

James.

 

[dilalio]

Sewers need a SVP more than they do an AAV.