Running Traps

rogermatthewstoby · 25 Oct 2014

The waste outlet on a new sink is lower than the old one, and fitting a standard p-trap would leave it lower than the existing pipework (so no natural run-off).

A solution would be a shallow trap (eg shower trap) which would then go into a running trap in the pipework, but I gather running traps are prohibited by most authorities. Any reason why? It would save re-routing pipework through the wall etc

Thanks

Roger

kidgreen61 · 25 Oct 2014

Can't you use an adjustable trap?

ie, a telescopic p trap

Dean744PiN5 · 25 Oct 2014

or use a short flexi to join trap to waste, as long as the existing waste isn't now level with the bottom of the basin otherwise water will just sit in the bottom of it.

rogermatthewstoby · 25 Oct 2014

Hi, thanks for reply.

Perhaps I misunderstand you, or maybe I didn't explain myself properly. A standard P-trap would leave me with an uphill run in the pipework. A telescopic trap would simply lower the outlet of the trap, making it worse!

Roger

PotatoHead · 25 Oct 2014

Just use a HepVo trap instead of any other, assuming you have the room to fit it.

rogermatthewstoby · 25 Oct 2014

Thanks for that PotatoHead - I didn't know of it. I'll look into it

However, it still doesn't answer my basic problem; a running trap would do the job just as easily (and cheaper) so why are they prohibited?

Cheers

Roger

Nige F · 25 Oct 2014

Prohibited on a USA site that popped up on google

I`ve never heard of them being prohibited over here

rogermatthewstoby · 25 Oct 2014

Thanks Nige F, unsurprisingly I'm no expert on the plumbing codes (though I do follow the main rules)

I wonder whether the problem with running P traps, with kitchen sinks, is that there is more risk of blockages occurring, given the stuff that goes down them. Presumably the further away from the bowl outlet, the less the pressure to carry it away around the trap, or even the more likely that fat and stuff will solidify?

Still, it provides such a tempting answer, I might try it; it will save lowering the whole pipework, knocking through walls, etc. It might come down to whether my kitchen fitters are in a hurry!

Cheers

Roger

longdogs · 25 Oct 2014

No problem with a running trap but not sure about using the shower trap. Does your sink waste go out through the wall and into a gully? If so, might be worth just lowering the whole waste a bit.

rogermatthewstoby · 25 Oct 2014

Hi Squeaky, thanks for post.

By 'shower trap' I mean a shallow P-trap ('U' shape). This will keep the outlet above the level of the existing pipework. Soon after the outlet it will enter a running trap, providing the water seal.

Once outside, the pipes go into a soil stack. I don't really get your point about the gully; as long as the running trap provides a water seal, does it matter?

I agree, in an ideal world I would lower the pipework, no problem, but I don't have the luxury of time, as kitchen fitters will be here and will want to get the units in (I certainly want them finished and out!)

Cheers

Roger

PotatoHead · 25 Oct 2014

rogermatthewstoby said:
Thanks for that PotatoHead - I didn't know of it. I'll look into it

However, it still doesn't answer my basic problem; a running trap would do the job just as easily (and cheaper) so why are they prohibited?

Cheers

Roger

I couldn't say if they were prohibited or not. To be honest I'm not even sure why I don't use them- I always use a HepVo trap where a trap is required in a unusual run, and I agree they are far to expensive for what they are.

JimCrow · 25 Oct 2014

rogermatthewstoby said:
Hi Squeaky, thanks for post.

By 'shower trap' I mean a shallow P-trap ('U' shape). This will keep the outlet above the level of the existing pipework. Soon after the outlet it will enter a running trap, providing the water seal.

Cheers

Roger

you cant have 2 traps in series, the sink wont empty.

rogermatthewstoby · 25 Oct 2014

you cant have 2 traps in series, the sink wont empty

Interesting. I'm not sure why not, though I can see there might be a risk of an air lock?

IN any event, I've decided, it's best to do the job properly. Lower the pipework and cut a new hole in the wall. There's enough of a drop on the outside to connect to existing pipework outside without having to cut a new hole in the soil stack.

It's a pain, but I'll just have to work around the kitchen fitters, whether they like it or not!

Thanks to everyone for their help

Roger

mfarrow · 25 Oct 2014

You need to come off the waste with a 90 bend. Maybe a 90 degree FxF galvanised elbow like this one http://www.bes.co.uk/products/160.asp?EPBOE=#8332

Brass may be better but more expensive... you can then screw in a plastic 40mm by 1.5" BSP male fitting you can then attach your running trap to.

rogermatthewstoby · 25 Oct 2014

Thanks mfarrow - I didn't know such things existed! But then I was looking at plastic fittings, and wondered why they don't make one.

It seems the running trap brings its own problems, I'll stick to the simpler, if longer way.

Incidentally, all this comes about because the plumber who fitted the new sink a couple of years ago, just made the connections at the sink. He must have known there was an uphill run on the pipework.

Cheers

Roger

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Running Traps

Dean744PiN5

longdogs

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