Air vent for stack pipe

[Keefiedee]

Have had a 3" 82mm stack pipe fitted to a toilet (+ basin) that never had one before and had a recurrent problem with suction emptying the waste traps, worsened when a shower was fitted.

This has 90% solved the problem, except occasionally - we think when the wind blows from a certain direction.

At present it has no kind of cap on it as the local builders merchant doesn't seem to be able to get hold of one that is 3" diameter.

I was thinking a cap in the form of a dome would be a good idea in that it would presumably avoid the possibility of the wind causing any further problems, but have been unable to find any for 3" pipe, only 4".

The only other option would seem to be an air admittence valve (e.g. Screwfix - FloPlast Push-Fit Air Admittance Valve Grey AF110, which fits 3" and 4") but I see from the Floplast website that these are not recommended for external use.

Any suggestions?

[Tim Watts]

Although that may not solve your problem, it might lessen it.

[Keefiedee]

Thank you for that. However ruminating on the problem I have come up with the answer myself - a 92½ bend, which could be fitted pointing away from the prevailing wind and would hopefully sort the problem. It will be a bit pricier than a vent cowl, but I have found a reasonably local builder's me rchant who has one in stock.

[Mike Clarke]

Or perhaps not. A series of strong gusts of wind from behind the bend might create enough suction to draw water out of the trap.

[Tim Watts]

If you can get a pushfit bend, then you have the option of adjusting it to get the best result. OTOH if you can only get a solvent weld bend, try it for a while without solvent - I suspect you may need a little trial and error here.

[harryagain]

I don't think wind would cause the problem. More likely incorrectly installed pipework or a part blockage somewhere. See if you can post pix and a link somewhere of the layout.

[David]

Given that the toilet should never have been installed on an un-vented stack in the first place.

I am assuming that the down pipe from the toilet is the standard size,

110mm?

The soil stack should always be vented and I think that if it is the only stack and the last one in the run it should be 110mm up and out.

If there is another stack upstream then you can use an air admittance valve (AAV) which is usually (always?) fitted internally. Please note again that you should not use an AAV if the soil stack is the furthest one away from the main sewer, at the end of the pipe run. In that case the run should be vented to the open air.

Then again Google turns up all sorts of arguments and suggests that 82mm external diameter may be O.K. for a vent pipe. This would be using the proper pipe designed for use as a soil vent. Google "82mm soil vent pipe" for examples.

Further Googling for "82mm soil vent pipe cap" turns up a number of different fittings which all look as though they should do the job.

If your local builders merchant can't get hold of a cap then either you have used the wrong pipe or the wrong builders merchant.

The susceptibility to wind action might be an indication that a full bore

110mm pipe might have been a better solution.

Cheer

Dave R

[Tim Watts]

I disagree - I went through building regs and found an 82mm was the minimum size of an end of run stack and was absolutely fine.

[Tim Watts]

And I should add, because I installed one at the end of my system. Though I do have a 110mm AAV on a mid branch by the loo.

[David]

Yes - it looks as though the regs allow it. However it may not be the best solution - the OP has stated there are problems.

[polygonum]

Use one of these on the basin - and another on the shower (if needed):

[Gazz]

"David" wrote

Is there a reason for an entire housing estate to have their bogs directly plumbed into the sewer with no vent stack??

Just wondering, as where i live, bungalows built between 1947 and 1949 all had a single bog of the S trap type with a floor exit, and the soil pipe is cemented into the floor and goes straight into the sewer via an inspection trap with an air tight lid.

Some of the bungalows have had new bathrooms fitted in the past 10 - 20 years, and they have the soil pipe going through the wall and a vent stack added, so i am thinking some regs changed or something? so that moving the position of the bog meant you couldn't just dig the floor up and move the soil pipe (or it's easier to go through the wall and dig the drive up, then fit a vent stack too)

I have not spotted any vent stacks in the streets.... like i remember from my grans house in York, a 1920's built house, and every few hundred yards there's a cast iron vent pipe from the sewers with a fancy spiked top to dissuade birds from nesting on it, they would gurgle and make other strange noises at times,

[Tim Lamb]

In message , Gazz writes

I have some vague belief that the *highest* connection in a system has to have a vent.

>

[David]

My recollection is that the stack furthest from the sewer has to have a vent, because that allegedly cannot fail.

If it had an AAV and that failed then the suction from mass bog flushings further down could be quite large (assuming they also had failed AAVs and not a vent)!

Anything nearer to the sewer can have an AAV because the suction is then localised to just that one pipe run and won't affect anyone else.

Seems like a logical design decision.

Cheers

Dave R

[Nightjar]

...

How much cast iron would have been needed to provide stacks to all of them? The post-war re-building lead to shortages of most building materials, a situation that, in some cases, lasted into the 1960s. There were a lot of short cuts taken to overcome those shortages in the late

1940s and throughout the 1950s.