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Unexplainable Results of Modeling AVs in Hammer

Hello.

I'm modeling a sewerage rising main of ID 409.2mm (HDPE - Wave speed: 327.22 m/sec. The system consists of:

1- Wet well.

2- Pump station (including GV, NRV,...)

3- Nos 3 AV (AV1 @ ST 0+000, AV2@ St. 0+300 and AV3 @ St. 1+000).

4- Outlet (discharge to atmosphere).

The pump station consists of 3 pumps (2 w + 1 stdby) to deliver 200 lps. The analysis was made for 2 scenarios as follows:

1- Scenario A: 3 pumps working - worst case scenario- (to size the surge tank and AV's).

2- Scenario B: 1 pump working (to check the negative pressure along the pipe route). The steady state HGL was showing a very minor negative pressure at AV2, and therefore, the "Treat Air Valve as Junction" was set to "yes". The negative head disappeared, and a small portion of the pipe downstream this AV was not running full (see HGL figure below).

Scenario A went successfully and a :Dip Tube Hydro-pneumatic tank" of 5000L is used to mitigate the negative pressure resulting from sudden power failure.

Scenario B was checked, and no severe negative pressure will take place. However, a non explainable velocity increase happens at AV locations (as seen below). This velocity increase is of coarse associated with discharge increase downstream of the AV. I extended the simulation period to a very large extent, but the discharge (and the velocity) never dies.

I can't understand the behavior of the line at the AV. I presume, this is an error in the software, that is separated the line into 3 separate segments and each segment behaves as if it's isolated. 

Can anyone help understanding this?

Appreciated.