Need help designing a tie into a 6" sewer FM?

[godiegogo]

We are the civil engineers for a new development that has a 6" sewer force main running in the right-of-way adjacent to the propoerty. There is no gravity main nearby. I do not have enough room for a septic system. I have never tried to tie into a force main directly. Can it be done? If so does anyone have any details? I was thinking that we could put a check valve on the service line before tieing into the force main.

 

[PEDARRIN2]

Unless the pressure upstream (gravity system) of the check valve was greater than the pressure downstream (force main), I would think the check valve would never open. And the only way to get pressure on the gravity system would be vertical head, which would mean that for every psi in the force main, you would need to be 2.31 feet above the elevation of the elevation of the check valve. If you have a fairly flat profile, you will have problems.

Also once the pressure equalized, the check valve would close and you would settle out in the piping.

What you might consider doing is provide a pit and pump as close to the force main as you can. Size the pump to overcome the pressure of the force main - to open the check valve but also it should not be more than the pump on the force main or you will back up that system.

Flow from your property via gravity to the pit.

 

[bimr]

The tie-in consists of a standard Y fitting.

I would not use a check valve located at the tee. The check valves are prone to failure and you would eventually have to dig it up.

Follow PEDARRIN2's lead. Put a small lift station outside the building. The discharge head must be higher than the pressure in the force main in order to discharge at all times. A check valve(s) should be located with the lift pumps.

If you have the lift station pump(s) located outside of your building, you will probably be able to sleep at night without the worry of a check valve failing and then leaking pressurized sewage back into your building.

 

[jartgo]

You'll also need to consider the headloss from both flows. That is, you'll be adding flow to a section of force main (which will increase the headloss through that section). So the head you'll be looking at will be the result of the sum of the existing flow and your new flow in that section of force main. Both pumps (existing and proposed) will need to be able to overcome the headloss from total flow.

 

[RWF7437]

Who owns this force main ?
Do you have permission to connect to it ?
What will the force main Owner require to allow you to connect ?
Is this part of a septic tank effluent system ( SREP) ?
Was this force main designed to allow connections to it ?
What does this force main serve now ?
Who designed it ?

good luck

 

[RWF7437]

Sorry about the typo; I meant STEP system.