40mm waste - min and max falls...

[xelaris]

I'm aware the maximum fall for a 40mm waste basin pipe is 44mm/m...
in my specific case I would need a steeper fall (maybe 80mm/m)...can I "cheat" the issue by installing the trap a bit lower?
This picture might give an idea:
http://www.ebay.co.uk/itm/280758616114?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

As you can see the trap is quite low...in fact there is a certain margin of adjustment which might help reducing/increasing the fall as needed.

Am I right?

 

[buck51]

Maximum fall?????

 

[xelaris]

Maximum fall?????

As you can see in this discussion the term "fall" indicates the "gradient" of the waste pipe...(do you know a better term? pls let me know).
http://www.ultimatehandyman.co.uk/forum1/minimum-fall-in-40mm-waste-basin-t25868.html

 

[Jackrae]

If 40mm is vertical fall is infinity so what's the problem. Fall rates in "horizontal" lines are, as far as i'm aware, to do with ensuring enough water continues to flow in the line to keep the sh*t and paper moving. Not likely to be the case in a 40mm line so the matter isn't relevant.

 

[xelaris]

If 40mm is vertical fall is infinity so what's the problem. Fall rates in "horizontal" lines are, as far as i'm aware, to do with ensuring enough water continues to flow in the line to keep the sh*t and paper moving. Not likely to be the case in a 40mm line so the matter isn't relevant.

if you check the link to that other discussion then it seems the matter IS relevant...

"The minimum fall for a 42mm pipe is 18mm per m. Maximum, 44mm per m. There are good reasons for these maxima and minima, to avoid blockages. If the fall's too small, the flow's too slow to keep the pipe clear; if too great you get turbulant flow instead of laminar flow and again the pipe may not remain clear."

 

[Jackrae]

But what length of 40mm line are you talking about. If only metre or so it's doubtful that laminar flow conditions will be established once the waste leaves the trap irrespective of the gradient. The fluid is turbulent when it enters the line so it needs length to establish laminar flow. Sometimes we get bogged down (excuse the pun) in bull**** and theory. If only a short length then gradient might well be irrelevant. Don't forget to instal the vacuum breaker line.

 

[xelaris]

But what length of 40mm line are you talking about. If only metre or so it's doubtful that laminar flow conditions will be established once the waste leaves the trap irrespective of the gradient. The fluid is turbulent when it enters the line so it needs length to establish laminar flow. Sometimes we get bogged down (excuse the pun) in bull**** and theory. If only a short length then gradient might well be irrelevant. Don't forget to instal the vacuum breaker line.

40mm is referred to the diameter of the waste pipe for basin/sink.....I've never referred to it as a "line"...then it seems the actual diameter is 42mm.

Bottom line is: can we control the "fall" by adjusting the height of the trap? It seems a simple question - but it appears you are questioning a question...again, I don't really know how relevant this issue is, but there are some guidelines which have been implemented for decades...

 

[GavThePlumber]

The minimum fall for a 42mm pipe is 18mm per m. Maximum, 44mm per m.

That is only partially correct, the regs state specific requirements for connection of branches in to soil stacks and for 40mm pipe, the slope is 18-90mm/metre over a maximum 3m. For the correct gradient, you need to refer to a design curve, this will at least you you an idea.

 

[denso13]

Bottom line is: can we control the "fall" by adjusting the height of the trap?

Yes, but you might not have to.

 

[denso13]

*double post*

 

[xelaris]

The minimum fall for a 42mm pipe is 18mm per m. Maximum, 44mm per m.

That is only partially correct, the regs state specific requirements for connection of branches in to soil stacks and for 40mm pipe, the slope is 18-90mm/metre over a maximum 3m. For the correct gradient, you need to refer to a design curve, this will at least you you an idea.

Ok, that 90mm/metre can really help my case....this because the waste from the basin is linked to the soil stack - and it's going to be less than 3 metres.
Maybe there is no need to lower the basin trap (the lower the more difficult to keep it out of sight too)...

 

[Fougere]

I appreciate this thread is 3 years old but people will still find it on a Google search. Just to add that the maximum fall is recommended as too vertical a fall over a distance can cause water to completely fill the pipe creating a vacuum that will then suck out the water from your u bend.