gravity connection to force main

[swolfman]

Existing 6 inch force main ties into manhole . From that manhole there is a 8 inch gravity sewer. Fl elevation at manhole is 59. Manhole lid is at 62.5 only 3.5 feet deep. There is a single family home at elevation about 76. It is currently piped into the manhole.

This will no longer be possible…long story…but road is going to be widened and it will be above road…so

We intend to tie gravity residential into force main…with sanitary sweep at like 2:00 maybe even into top of force main….at about elevation 49. Distance from tie in to manhole is about the same distance as to the home about 100 feet. Plan to put a check valve (ball check) on the gravity 4 inch pipeline above manhole cover elevation.

I figure that when pump is not on gravity flow will push as a siphon into manhole. When the pump comes on what will happen…Will it pull with a vacume?

Any thoughts on this plan?

 

[bimr]

Sounds like a bad idea.

What will happen when the check valve fails? Maybe several hundred gallons per minute flowing into a residence.

The check fail may wear out over time or become jammed with debris.

Have you considered installing a small eone lift station at the residence?

 

[swolfman]

The manhole that the the force main pumps to is well below the house and will be below the check valve. The check valve will only be needed if the force main collapses between the residential connection and the manhole.

 

[dicksewerrat]

I would follow the advice of BIMR. You can't afford the lawsuit when one of the kids living in the house gets sick.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[swolfman]

sick???? from????

 

[atook]

You've only got 16' elevation from the FL at manhole and the residence. I imagine your lift station generates more than that?

I don't do much sanitary work, but in my line of work, it's not uncommon to see check valves get stuck open from debris. If the valve is stuck open, and the pump comes on, life could get very exciting in that house.

An E/One lift station for the residence may be more expensive, but seems like a safer route.

Tim Grote - The Irrigation Engineers.

http://www.irrigationengineers.com

 

[Maury]

Your last statement and question: "I figure that when pump is not on gravity flow will push as a siphon into manhole. When the pump comes on what will happen...Will it pull with a vacume?"

The pump will not pull a vacuum, it will cause a back pressure on the check valve until the valve fails, which it will cerainly do at some time. If I am reading your numbers correctly, there is a low point in the force (elev. 49, where you plan to make the service connection) before it discharges to the manhole at elev. 59.0, and the force main never completely drains. You will be depending on the flow from the house developing enough head to keep the service line and check valve from clogging.

I don't see anything good about this plan.

 

[dicksewerrat]

swolfman, When was the last time you walked in a sewer? up to your waist? Did you wash off before going home? Typhoid, typhus, cholera, yellow fever, plague. Just make a list of all the diseases in a third world country.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[swolfman]

well we have installed the gravity lateral to force main and it is working just fine...I kinda appreciate your replies but none were really based on engineering just fear. check valve is not even active since it is above force main outlet elevation.

 

[bimr]

I do not use a fear factor. Opinions are based on common sense, practicality, experience, compliance with building codes and regulations, and murphy's law among other things.

I took the question to ask if you should consider a check valve as a tight shut-off, leak tight valve that would prevent the discharge pressure of the running force main pump from pressuring up the gravity line. If that is the question, the answer would be no.

In a HAZOP analysis, one does not take any credit for a check valve.

Good luck to you. Be sure to keep your mobile on.