Calculation of discharge pipes (sewage disposal)

[Christophe]

What are the rules for sizing a wastewater evacuation in order to avoid clogging and stagnation at the "source"? Minimum slope? Diameter of pipes / maximum flow rate of the source? Sizing of the siphon?

Anyway, I know quedale and I would like to know how we size a landfill?

Goods.

[Forhorse]

There are undoubtedly calculations, but in general according to the connected equipment one always puts the same thing.
What is important is the slope (in general a good slope like 2% avoids the problems)
Then we modulate according to lengths or conditions.

For example when PVC pipes are buried they quickly tend to crush and take the form of a very flat oval reducing therefore the passage with the foreseeable consequances that it can have.

But generally the longer it is the more the diameter is increased.

some standard diameters:
bathroom sink; bidet: 32mm
shower, sink: 40mm
bathtub: 50mm
WC: 100mm

this remains valid for short horizontal links (4 to 5m) with a good slope.
Then we go to the upper diameter
32-> 40
40-> 50
50-> 80
100-> 125
125-> 140
140-> 160
etc ...
And of course the longer it is, the larger the diameter.
Many plumbers and good do-it-yourselfers do this with judgment, with habit.
But it is certain that there must be abacuses or calculations.
After that it depends on what exactly you want to do.

[Christophe]

Thank you Forhorse for the very general and complete answer as it should be

I don't have any special needs but I just wanted to know what was being done in this area ...

With us "everything" (bathtub shower ... except WC obviously) is 32 mm, even in the "final" portions ...

I noticed that there was a vent that overlooks the foliage ... does anyone know its usefulness? Avoid engorgement?

ps: hey trap question and for a sanibroyeur? What do we count?

[Forhorse]

It's weirdly done, in principle for each point we try to connect the pipe as short as possible to a larger manifold (often in 100mm)

The event can have two uses (one, the other or both):
it can be the primary ventilation of the tank (septic or all waters) but normally this ventilation must now be done in minimum 80mm (before the 90s it was often 40)
it can also be an event which avoids emptying the siphons in the event of a vertical fall. Indeed, without this event, the fall of the water causes a depression in the pipe which has the effect of sucking the contents of the siphons which suddenly lose all utility.
(To avoid this we can also put special calpets.)

Otherwise, to come back to the calculation of pipe diameters, I think that we may have to look for the roof descents for rainwater. Depending on the roof area there must be abacuses which determine the number and / or the section of the downpipes, or calculation notes, since we do not put the same thing for a garden shed or the roof of a 6000m² shopping center

EDIT: a yes for sanibroyeur it is often in 32 or 40

[dedeleco]

I noticed that there was a vent that overlooks the foliage ... does anyone know its usefulness? Avoid engorgement?

Basic for any plumber. To not forget !!
Otherwise, without vent, strong overpressures and depressions of air occur, the flows are very bad, in the sinks and toilets, the other siphons serve as vents by emptying with these overpressures and depressions and the stinking odors come out !!
Finally these vents must be the highest, in a well ventilated place otherwise odors and stinks if we put them lower !!
I was made to put them lower, towards the outside and smells of stench enter the bathroom, through a wall that is not waterproof, especially with the wind !!

[Christophe]

Yes, quite odd, hence these questions but well it works ...

After asking the question, I reflected a bit and I actually think that this is especially your second explanation because there are many vertical conduits.

On the other hand, as this vent is 32mm, it still creates a sacred "thermal bridge" ... so I wonder if it would not be wise to put an automatic degasser at the high point to limit the intake of fresh / cold air? ?