I have a kitchen sink (and dishwasher) that is some distance
from the gulley. I can find web pages that recommend 1 in 40 to
1 in 120 as the range of gradients that work best on the grounds
that solids will be stranded as the liquid flows too fast if the
gradient is too steep or settle out if its too gentle. I think
this is mainly for sewage. Does this really apply to the grey
water that one gets out of a kitchen sink?

Im moving the pipe because it blocks frequently and is hard to
get to to unblock. It currently drops through the bottom of the
sink cupboard and then runs along and turns a corner under the
cabinets before going out through the wall. The main problem
seems to be that a biofilm forms on the inside of the pipe, and
I would have thought that having the liquid flow past quickly
and dry out as much as possible would be the thing to go for.

Any ideas?

--
Jón Fairbairn
http://www.chaos.org.uk/~jf/Stuff-I-dont-want.html (updated 2014-04-05)

On Wed, 21 May 2014 09:47:44 +0100, Jon Fairbairn wrote:

I have a kitchen sink (and dishwasher) that is some distance
from the gulley. I can find web pages that recommend 1 in 40 to
1 in 120 as the range of gradients that work best on the grounds
that solids will be stranded as the liquid flows too fast if the
gradient is too steep or settle out if it s too gentle. I think
this is mainly for sewage. Does this really apply to the grey
water that one gets out of a kitchen sink?

The building regs have reasonable detail on the required falls and
pipe sizes. I think it's Doucment
H:

http://www.planningportal.gov.uk/bui...roveddocuments
/parth/

URL may well be broken but I'm not makinga tinyURL for 3 characters.

--
Cheers
Dave.

Dave Liquorice wrote:

http://www.planningportal.gov.uk/bui...roveddocuments
/parth/

URL may well be broken but I'm not making a tinyURL for 3 characters.

No need :-)

http://planningportal.gov.uk/buildin...ocument/parth/

"Dave Liquorice" writes:

On Wed, 21 May 2014 09:47:44 +0100, Jon Fairbairn wrote:

I have a kitchen sink (and dishwasher) that is some distance
from the gulley. I can find web pages that recommend 1 in 40 to
1 in 120 as the range of gradients that work best on the grounds
that solids will be stranded as the liquid flows too fast if the
gradient is too steep or settle out if its too gentle. I think
this is mainly for sewage. Does this really apply to the grey
water that one gets out of a kitchen sink?

The building regs have reasonable detail on the required falls and
pipe sizes. I think it's Document
H:

Thanks. Looking through it I cant find anything specific to the
case. This is going from the sink into a gulley, so its vented
and not a branch. The permitted gradients for branches do go up
to 1 in 20, though.

URL may well be broken but I'm not makinga tinyURL for 3 characters.

Gnus can unsplit URLs, so it doesnt bother me.

--
Jón Fairbairn
http://www.chaos.org.uk/~jf/Stuff-I-dont-want.html (updated 2014-04-05)

On 21/05/14 15:41, Jon Fairbairn wrote:
"Dave Liquorice" writes:

On Wed, 21 May 2014 09:47:44 +0100, Jon Fairbairn wrote:

I have a kitchen sink (and dishwasher) that is some distance
from the gulley. I can find web pages that recommend 1 in 40 to
1 in 120 as the range of gradients that work best on the grounds
that solids will be stranded as the liquid flows too fast if the
gradient is too steep or settle out if its too gentle. I think
this is mainly for sewage. Does this really apply to the grey
water that one gets out of a kitchen sink?

The building regs have reasonable detail on the required falls and
pipe sizes. I think it's Document
H:

Thanks. Looking through it I cant find anything specific to the
case. This is going from the sink into a gulley, so its vented
and not a branch. The permitted gradients for branches do go up
to 1 in 20, though.

The long and short is "fall along all of the pipe" is essential.

It's ideal if the fall is "good" - but no fall (or worse a sag) will
cause blockages. A continuous fall, even if not ideal is usually manageable.

If good fall cannot be achieved, run the pipe in 50mm and stick some
tees with a screw cap end to act as rodding points.

Tim Watts writes:

On 21/05/14 15:41, Jon Fairbairn wrote:
"Dave Liquorice" writes:

On Wed, 21 May 2014 09:47:44 +0100, Jon Fairbairn wrote:

I have a kitchen sink (and dishwasher) that is some distance
from the gulley. I can find web pages that recommend 1 in 40 to
1 in 120 as the range of gradients that work best on the grounds
that solids will be stranded as the liquid flows too fast if the
gradient is too steep or settle out if its too gentle. I think
this is mainly for sewage. Does this really apply to the grey
water that one gets out of a kitchen sink?

The building regs have reasonable detail on the required falls and
pipe sizes. I think it's Document
H:

Thanks. Looking through it I cant find anything specific to the
case. This is going from the sink into a gulley, so its vented
and not a branch. The permitted gradients for branches do go up
to 1 in 20, though.

The long and short is "fall along all of the pipe" is essential.

Sure. I have no problem getting it steep enough. What Im
wondering about is the upper limit on how steep it should be.

--
Jón Fairbairn
http://www.chaos.org.uk/~jf/Stuff-I-dont-want.html (updated 2014-04-05)

On 22/05/14 09:19, Jon Fairbairn wrote:

Sure. I have no problem getting it steep enough. What Im
wondering about is the upper limit on how steep it should be.


None really.

On 22/05/2014 09:46, Tim Watts wrote:
On 22/05/14 09:19, Jon Fairbairn wrote:

Sure. I have no problem getting it steep enough. What Im
wondering about is the upper limit on how steep it should be.


None really.
That's certainly always been my view but my kitchen sink outlet runs for
about 10ft with a shallow slope, through a wall, then vertically for a
foot, through a 90 degree turn then along another couple of feet of
shallow slope to the gully. Dunno if that's the cause but it makes some
pretty 'orrible gurgles when the sink's emptied and I've been meaning to
have a fiddle with the geometry for ages to see if it has any effect.

On 23/05/14 00:22, GMM wrote:
On 22/05/2014 09:46, Tim Watts wrote:
On 22/05/14 09:19, Jon Fairbairn wrote:

Sure. I have no problem getting it steep enough. What Im
wondering about is the upper limit on how steep it should be.


None really.
That's certainly always been my view but my kitchen sink outlet runs for
about 10ft with a shallow slope, through a wall, then vertically for a
foot, through a 90 degree turn then along another couple of feet of
shallow slope to the gully. Dunno if that's the cause but it makes some
pretty 'orrible gurgles when the sink's emptied and I've been meaning to
have a fiddle with the geometry for ages to see if it has any effect.

Another way to handle this (and the preferred way on sewer pipes where
there are maximum falls quoted in building regs) is to run on a sensible
slope, then a 90 degree bend with a gentle bend at the bottom (not a
tight elbow) then continue with a run at a reasonable fall again.