Air lock in waste system

[bally74]

I hope someone can help

I had an existing kitchen, with the sink waste running into an un-vented 40mm stack, this went through a u-bend. the washing machines waste always had trouble when it was above the sink ubend so now it is connected directly to the top of the small stack, all goes well.

I have now fitted a shower and basin into the same room.
The basin has an anti syphon bottle trap and the shower uses an Hep20 valve, this runs into the same stack at it's lowest point.

The basin has no problem draining at all but the shower tray eventually overflows, I didn't think it was a vacuum problem due to the Hep20 valve and the anti siphon trap on the basin being able to let air into the system.
However when my washing machine connection is removed and the stack is open to the air, the shower tray drains away perfectly. I think my problem is more positive pressure than a vacuum problem.

A local plumber gave a solution to run the stack outside and have it permanently vented, which is good advice and would cure the problem, the thing is I'm lazy and was hoping that there was a magic valve I could put into the system that would allow the air to escape.

Any ideas anyone?

 

[lukechrissy]

Air Admitance Valve

 

[Nige F]

Air Escape Valve

 

[imroberts]

http://www.screwfix.com/app/sfd/cat/products.jsp?id=42968&ts=89176

 

[bally74]

Thanks for the replys.
An air admittance valve wouldn't actually work as the air needs to escape, it's positive pressure.
I did test for this by holding over a piece of clingfilm over the top of the pipe when the shower was draining and it bulged out.

An air escape valve would work but i don't think these exist on waste systems due to smells/gases being under positive pressure and being able to escape into the room.

I have bit the bullet and fitted a vent which runs outside and this has worked, just need to extend it up higher now for some legal thingy.

I did actually phone a few plumbing supply shops and they stated that positive pressure wouldn't exist and that I would only need an AAV, however it seems they are wrong!

 

[gigz]

Could you not have tried an AAV first

 

[Nige F]

Thanks for the replys.
An air admittance valve wouldn't actually work as the air needs to escape, it's positive pressure.
I did test for this by holding over a piece of clingfilm over the top of the pipe when the shower was draining and it bulged out.

An air escape valve would work but i don't think these exist on waste systems due to smells/gases being under positive pressure and being able to escape into the room.

I have bit the bullet and fitted a vent which runs outside and this has worked, just need to extend it up higher now for some legal thingy.

I did actually phone a few plumbing supply shops and they stated that positive pressure wouldn't exist and that I would only need an AAV, however it seems they are wrong!

Well done M8- you have more sense than a lot of "plumbers" - and definitely more than my ex next door neighbour -A Builder- He had a whole 4 inch soil blocked because of positive pressure . I just undid a cleaning cap on a waste tee - away it went - no rods needed - Way back they used to run " puff pipes " in lead right out through roofs etc to vent - both + and - pressure . But that and any form of skill is all gone now - you just need to be Gas Safe Registered PS The escape valve was a wind - up