Force Main Manhole

[KLH]

Hello all,

Can someone tell me the purpose of the 4-inch long vent at the top of the tee where the force main enters the manhole? Please refer to the attached detail.

With the force main pump on, I think there would be sewage flying all around inside the manhole.

Thanks in advance!
Ken

 

[bimr]

The drawing is not correct. Someone has confused gavity flow sewers and pressure sewers.

A pressure force main should not enter a drop MH with a drop connection. Force mains generally enter about 2 feet off the bottom and the flow should be directed in the same direction that the sewer is flowing.

Some sewer districts will not allow a service connection to enter through a manhole either. Service connections are generally required to enter the sewer line.

I think that you should contact the sewer authority and get connection advice directly from them. The drawing is incorrect.

Another option may be to install a small residential MH and transistion from force main to gravity sewer in that MH.

 

[KLH]

Thanks bimr. I appreciate your help.

We are actually designing the plumbing inside the building and the architect asked us to pick up the outdoor piping as well, including the transition from the force main to the gravity system. I thought a manhole would be the ideal transition and found that detail on an a major US city's website.

This work is now out of my area....I'll tell the architect to hire a civil engineer.

Thanks again.

 

[cvg]

on private property, you can do what you wish, the sewer district does not control your onsite sewer system. a more typical installation is to a wye connection with a cleanout and then gravity flow to the gravity sewer line.

you are correct though, this would typically be outside of the MEP limits, the battery limits are typically 5 feet from the edge of the building and the civil engineer picks up everything outside of that limit.