Connecting force main to gravity main 4

[POLYENGMOR]

Hello fellow engineers,

I work on a project where I need to connect a force main to a gravity main via a manhole (attached drawing).

https://files.engineering.com/getfi...-1b61-4caf-b5fd-6ca3aca97f4e&file=manhole.JPG

Is this design correct?
Are there any rules I need to take into consideration regarding the difference between the level of the force main and the gravity main? (In my case the force main is 30cm higher than the gravity main (outside the manhole), is it a good thing?
Are there any rules I need to take into consideration regarding the height of the weir between the two parts of the manhole?
Do I need to make the manhole larger?

This is the first wastewater project I'm working on so please forgive me if my questions are dumb .

 

[bimr]

You can go straight into the gravity sewer without that sump. See the link.

Link

 

[Pinwards]

I agree with bimr, you want to direct that FM discharge towards the gravity pipe opening as smoothly as you can. As drawn you are going to have a splattering mess all over that manhole (depending on exit velocity) and that "sump" will be constantly full of waste and an odor issue.

#

 

[TigerGuy]

Can you tap the force main discharge into the gravity line, separated from the manhole? I've only been involved in one force main design, but that's what we did. It discharges into the gravity line and transitions into gravity flow. There's no pressure when it reaches the manhole.

 

[AgMechEngr]

There is more than one way to skin this cat, but I would elect to do whatever the public authority over the utility requires. It is common around here for the force main to enter the manhole with an elbow turned up once inside the manhole.

 

[FacEngrPE]

Lots of ways to make the connection between pumped sewage and gravity. Often the public utility will have a standard approach.
From the standpoint of long term durability, reducing turbulence in the section where excess energy is dissipated will reduce H2S production, and erosion of the structure and piping.

If you need to enter a manhole with a forcemain, and your starting elevation is high on the wall, consider using an inside or outside drop connection.