drainage

Joined
2 Aug 2008
Messages
28
Reaction score
0
Location
Selkirkshire
Country
United Kingdom
Hi

I hope this is the right section for asking a drainage question

Recently i have had a new building put up, it is a car workshop, i would like a second opinion before i raise my doubts with the contractors, i dont like to complain but if it is wrong i will raise the points with them.

Our waste from the toilets is getting stuck in the first section of drainage
drain A to drain B.

My step son who does building work has been out and measured the depths with a dumpy level at all the drains.

From the measurements we took it would seem there is not enough run on the first section dain A to drain B, and more than enough of a run, from drain B to drain C AND C to D.

I have attached a drawing it is not to scale but the measurements and drops from drain to drain are correct.

I suppose i want to know is could more of run been achieved drain A to B if the run was less between point B to D as the run's dont seem consistent, and the run drain A to B if it were minuim 1 in 10 drop 58mm would only span a distance of 5.8 meters and the distance is 7.9, am i right as i really dont know that much about this kind of thing

.
DRAINS.jpg
 
Sponsored Links
The invert at B needs to be lowered by at least 40mm, the invert at C needs to be lowered by 10mm to achive falls of 1:80.
 
The overall fall is enough to achieve the required falls. Ideally the run would have been consistent for the whole run and would have been 1:68 from A-D.

They have put B in too high for some reason! Realistically lowering invert C for the sake of 10mm is likely to be impracticable.

Are you sure there is nothing in the pipework holding up the turds? Like a blob of mortar or similar.
 
Sponsored Links
The overall fall is enough to achieve the required falls. Ideally the run would have been consistent for the whole run and would have been 1:68 from A-D.

They have put B in too high for some reason! Realistically lowering invert C for the sake of 10mm is likely to be impracticable.

Are you sure there is nothing in the pipework holding up the turds? Like a blob of mortar or similar.

No :( unfortunately there is nothing in the pipe the turds are just sitting right at the end of section A just before drain B

What is the run between A and B as it is at the moment, i dont know how to work it out :oops:

In fact if you have the time can you tell me drop of each run

A to B
B to C
C to D
 
OK in an ideal world with an overall drop of 520mm over a distance of 35500 (7900 + 9600 + 18000) the fall would be (35500 ÷ 520) 1:68.

Therefore

A to B 116mm (7900 ÷ 68 )
B to C 141mm (9600 ÷ 68 )
C to D 264mm (18000 ÷ 68 )
 
OK in an ideal world with an overall drop of 520mm over a distance of 35500 (7900 + 9600 + 18000) the fall would be (35500 ÷ 520) 1:68.

Therefore

A to B 116mm (7900 ÷ 68 )
B to C 141mm (9600 ÷ 68 )
C to D 264mm (18000 ÷ 68 )

Thanks i really appreciate the info and taking the time to calculate it for me.
so you will have to excuse me as i ask another couple of layman type questions.

The dimensions you mention above are depths that could be achieved over the drop between drain A and drain D ??

The measurements you mention between b to c and c to d, dont seem a million miles from what is there.

Where did it go wrong at A to B as that point seems to be a mile away.

One more thing i am probably missing the obvious here as i can be a bit thick when it comes to maths lol.

What are my drops as they stand at the moment, particularly intrested in drain A to drain B what is the run on that drain at the moment with 58mm of drop over 7.9 meters.

Again thanks for your help
 
The drops quoted in my last post are what could have been achieved.

Yes you builders have put the invert at B in too high.

At the moment

A to B is a fall of 1:136 (7900 ÷ 58 )
B to C 1:73 (9600 ÷ 151 )
C to D 1:60 (18000 ÷ 298 )
 
A to B is a fall of 1:136 (7900 ÷ 58 )
B to C 1:73 (9600 ÷ 151 )
C to D 1:60 (18000 ÷ 298 )

so does that mean

A to B drop's 136mm every meter

B to C drop's 73mm every meter

C to D drop's 60mm every meter

And one more layman type question i promise :) i notice on your calculations you divide length of the run 35.5 meters by the depth 520 mm.

Somebody else told me i could work it out by dividing depth by length witch is the opposite to these calculations, i am getting confused now lol.

I am not doubting your calculations just wondered why i have been told i can divide it the other way round.

This is the last question i promise dont want to waste anybody's time

Thanks for all your help
 
Somebody else told me i could work it out by dividing depth by length witch is the opposite to these calculations, i am getting confused now lol.

That would give you the inverse of the figure that you require, (i.e. 1/x)
(Inverse is nothing to do with invert in this context)

So:
58 ÷ 7900 = 0.007341772 (to 9 decimal places)

But as this is the inverse figure, you'll need to divide that figure into 1
So:
1/0.00734 = 136 approx.

Don't worry if you don't understand it, just accept that fmt is correct.
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top