Reducing pipe size at an inline air release valve in pressure sewer

[jffr602]

Our firm was called out to consult on a private sewer system malfunction. Each house in this development is equipped with grinder pumps which pushes the waste water through HDPE lines ranging from 1.5" to 3". In line flushing stations occur every 1000 feet typically. At the high points in the lines, 2" combination air release valves are installed in manholes. However, when an ARV is installed on a 3" line, it is reduced to 2", converted to brass within the manhole, and upon exiting the manhole re-sized back up to 3" HDPE. The HOA has a drawing detailing this downsize, but I don't understand why the pipe diameter would have to be reduced. Wouldn't a 3"x3"x2" brass tee allow for the 2" ARV to be installed without causing a "bottleneck" at these locations.

 

[bimr]

The manufacturer is probably using a standard setup and has put little thought into the application.

There is no reason to decrease the pipeline to 2-Inch to install an air release valve. In fact, unless concentric reducers are used, the 2-Inch reducers could be trapping air as the force main narrows.

However, there is probably not a significant friction loss associated with the use of 2-Inch fittings unless your are dealing with multiple fittings on the same force main. There should not be much concerned with clogging either since everything has been through grinder pumps

In addition, there is no reason that brass fittings have to be used. A saddle fitting on the force main would be acceptable.

In general, automatic air release valves should not be used on force mains. Air release is necessary only on startup and can be done manually. Refer to the attached articles.

http://files.engineering.com/getfil...411c-4ba5-b72b-e62f13744789&file=0362_001.pdf