Grit pumping

[Sam1390]

Hi ,
I am working on a waste water treatment project, we have a Grit Chamber at higher level comparing the downstream Grit classifier , the Grit pumps to push the grit from chamber to classifier is located at the bottom of Grit chamber. in our P&ID , there is a barometric loop that raises up grit and then return it back to the classifier . similar to the photo attached. Just wanted to know the reason of having this loop when the grit chamber is located at the higher level comparing classifier and we are having a vacuum breaker valve on top pf the loop as well.
Does anyone know the reason?

 

[bimr]

Assuming the pump is a typical centrifugal pump, you would have gravity continuing to cause flow through the pump (around the pump impeller) with the power off.

 

[SteveWag]

The vertical loop, vented at the top, presents a constant head situation to the pump. The vent at the top can just be an upended tee. Grit pumps are normally open or recessed impellor pumps. and they work best if there is some minimum head available.
Steve

 

[bimr]

Consider installing an automated valve that closes when the pump is not operating.