Connecting Forced Main to Gravity Main
Connecting Forced Main to Gravity Main
(OP)
I am designing a sanitary system in which I am being asked to provide a 2" forced main from a duplex grinder pump and connect it into an existing 4" sanitary line that is gravity-fed. I know that the 2" line will require a check valve per the manufacturer specs, but since this is planned to be all underground; are there any further requirements for the forced-main-to-gravity-connection?
In the past we have pumped a force main up to an overhead sanitary gravity pipe where we dropped into the gravity pipe after the check valve.
Am I right in the thought that a similar system would have to be designed for this; but underground?
Thanks (in advance) everyone!
In the past we have pumped a force main up to an overhead sanitary gravity pipe where we dropped into the gravity pipe after the check valve.
Am I right in the thought that a similar system would have to be designed for this; but underground?
Thanks (in advance) everyone!





RE: Connecting Forced Main to Gravity Main
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Connecting Forced Main to Gravity Main
dicksewerrat has a good point that you may be forced to do whatever the gravity line's owner requires. Sometimes there can be negotiation, because a manhole is proportionally expensive and may not be required in this case. The gravity line owner may want a manhole simply for ownership demarcation purposes.
You also need to find out the material, condition, and age of the gravity line. Tapping into new PVC is a different issue than old asbestos pipe, for example.
RE: Connecting Forced Main to Gravity Main
At this point I am providing a backwater valve within an access panel per the building owners request. I just wish they said so right off the bat haha!
RE: Connecting Forced Main to Gravity Main
You should also check with the owner of the 4-Inch line to be ascertain if he has any requirements for the connection.
RE: Connecting Forced Main to Gravity Main
RE: Connecting Forced Main to Gravity Main
Not sure on the configuration of your installation but here is another solution for future reference. Certainly a structure would be needed at the interconnection with the gravity lateral or main, just not sure that it is necessarily a manhole, maybe it can be smaller box like shown in the detail. See attached file from local agency.
RE: Connecting Forced Main to Gravity Main
I wouldn't think you would need a manhole at the connection. Most grinder lift stations can accommodate a check valve at the pump.
I would put the check valve as close to the pump as you can.