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Discuss How to fix positive pressure and add a dishwasher? HepVO? Away from sink? in the Plumbing Jobs | The Job-board area at PlumbersForums.net

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mfripp

We live in a second floor flat, with one more floor above ours. Our kitchen sink drains into a 40mm PVC pipe that goes directly to a soil stack about 1.5 meters away. In our flat, the kitchen sink is the only drain connected to this soil stack (there's a separate one for the bathroom). However, I don't know whether there's a kitchen or bathroom connected to this soil stack in the flat above ours.

Our problem is that we sometimes get a glugging noise and wastewater splashing up from the kitchen sink trap into the sink. It's disconcerting, and occasionally accompanied by a bad smell. I imagine it may be due to poor venting of the soil stack, causing positive pressure when water rushes down from the flat above, but I haven't investigated that.

For now, I'm looking for solutions to this problem that I can implement within our flat. I am also looking for a way to connect a dishwasher into this system, and to maintain as much space under the sink as possible, for sliding rubbish bins.

I've bought a HepVO trap and installed it horizontally immediately under the sink. This has stopped the glugging, and keeps the drain pipe nicely close to the bottom of the sink. Unfortunately, in the horizontal position it doesn't seem to drain quite as fast as I'd like (although it's tolerable), and a little bit of smelly water may be remaining upstream of the trap (possibly when soapsuds are the last thing down, and they hold the trap open a bit for smells to come back up?). These aren't big problems, but they've gotten me thinking the HepVO might perform better if it were mounted vertically on the back wall instead of horizontally under the sink. Does that sound like a good idea? Or would that leave too much horizontal pipework before the trap (e.g. could food and wastewater get smelly in the pipes between the sink and the trap -- 30 cm horizontal and 15 cm vertical)?

The second question is, what's the best way to add a dishwasher waste into this setup? I could add an appliance adapter (like this: Appliance Trap Adaptor 40mm - Screwfix.com, Where the Trade Buys ) below the sink, but that would push all the pipes down further than I want. On the other hand, if I move the HepVO to the back wall, I could put a T above it and send both the dishwasher and sink waste down through it.

Alternatively, I could add a separate appliance upstand and trap for the dishwasher, but I'm worried that the occasional positive pressure could be a problem (maybe less so with the 30 cm upstand), or that the trap could empty if we don't run the dishwasher for a while and/or water gets siphoned down the soil stack.

Any suggestions on the best way ahead?
 
Hi. Its standard practice to use a trap and upstand. In your case important that the upstand open end is high enough that any back flow enters the empty sink, before overflowing out of upstand.
However i would be inclined to investigate existing problems before any alterations. It is most unlikely that one flat above would cause the problems you describe if the soil system was in good order and installed to a standard. There are three types of soil pipe arrangements, two pipe, one pipe and single stack find out the system employed. The positive pressure may be caused by compression ( a sharp bend or blockage/restriction at a point just below the 40 mm branch to sink.) Good Luck
 
hi,

i would fit a standard anti-syphon trap below the sink this will protect from bad smells by always retaining a seal depth. it will also protect your trap from being blown through the waste and into the sink.

fit the standpipe type washing machine trap down stream and if possible downstream again from this i would fit a small 'running trap' assuming it is going to be hidden by units, washer etc. the compression problem you describe will probably abate as a result. the small running trap may blow its seal but the displacement shouldn't be enough to blow the washing machine trap upstream. because the sink is now protected any water from traps blown upstream will flow back down and find its level in the traps creating a seal again.

either making or creating a running trap is not going to break the bank so this is what i would try.

the problem you describe is common in flats, basically the waste from above is running full bore in the stack before it reaches your branch so it is pushing air up your branch and blowing your seal.

another method to solve this would be to employ the branch ventilation system whereby your branch upstream from the stack would be fitted with a tee. a pipe would rise from the tee then angle in and connect into the stack. as waste from above running full bore pushes air up your branch discharge pipes instead of blowing your traps the air will now be forced up the tee and back into the stack above the 'plug' of waste water because air offers less resistance to the water in your trap.

i would try the trap option first because it will be the cheaper option, and you can diy it. but the second option is definitive.

hope this helps!

KJ:)


p.s if you are friendly with the bloke upstairs ask him to adjust his flushing mechanism on w/c (many have three settings) or failing that get him to stick half a brick in the w/c cistern (not good practice but may offer a quick fix at no expense!)
 
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Thanks very much for these comments -- it's great to get ideas from the pros! I now have a couple more questions:

(1) Neither of you mentioned the HepVO -- does that mean you don't generally recommend it? I can see the appeal of sticking to tried and true, especially since there's no telling whether the HepVO approach will still be working in 10-20 years.

(2) The stack in the kitchen actually has two 40mm bosses on it. The upper one used to go to the kitchen sink, while the lower one went to a clothes washer (which has been removed). The upper one has now been capped and I'm using the lower one for the sink, since it provides a more direct line. The capped connection is about 18 mm above the branch that goes to the sink. Could I take a T off the lower branch, connect it into the upper connection and create a satisfactory branch ventilation system? Or does the vent pipe need to connect higher than that?

Thanks again! I'm sure I'll have more questions as I get further into it!
 
1 hepv0 are fine in the vertical position but i would only use them in basins where the worst they cope with is a bit of soapy water. i would not reccomend them for a sink which drains with bits of food etc which could and usually will compromise the seal particularly in a horizontal position.

2 depends how much difference in height position the 2 bosses are?? remember to be effective the soil stack between the 2 bosses needs to be capable of accommodating the volume of water that causes the problem. in this case the w/c flush will be about 6 litres if upstairs toilet is modern ish and maybe 9 litres if its old ish.

if the pipe cannot accommodate the wc flow the air will continue to blow your trap because the air will push against both the remainder of its own volume and your trap seal. your seal offering less resistance will still blow.

hope this helps.

KJ
 
Thanks again! I'm now thinking about using a standard trap under the sink and a standard appliance trap/upstand for the dishwasher. Then I may add the HepVO downstream of both of them (since I have it already) -- that should definitively stop air coming back up through the traps, and there shouldn't be any problem if it seals incompletely, since it's below the water traps.

Sorry I reported the distance between the two bosses incorrectly -- they are 18 cm apart (not 18 mm!). As far as I can tell, it's a 10cm pipe, so that only allows about 1.4 liters between the two bosses -- won't really do the job!

Best,

Matthias
 
ok, let us know how you get on. be aware that the problem of bits of food etc keeping the hep membrane from sealing could still be an issue. for best results try and find a vertical position for it.

good luck

KJ
 
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