Designing for Suction Flow

[lcw818]

1. When calculating NPSHa: Do you use theoretical suction lift 33.9 feet or practical suction lift around 25 feet sea level?
2. I have an 8-inch suction line that is horizontal at the pump location and below the inlet to the pump. the pump is a 3in x 3in so I have a concentric reducer from the 8-inch to 3-inch. Currently it is also horizontal then goes thru a 90 and up to the level of the suction inlet on the pump. There is concern we are trapping water in the top of the concentric reducer. Can I turn this reducer up to vertical?

luke

 

[MJCronin]

1. When designing for suction lift, talk with the pump vendors first and see what thier pumps can do.... In my opinion, 20 ft lift is about the limit. Also consider how often the pump will cycle and how you will prime the pump. A self primer may be gthe way to go Vertical cantilever pumps (with reasonable sump depths) make a lot of sense to me...

2. When the pump is above the sump (i.e. suction lift conditions) or if the pump is drawing from an adjacent tank, an eccentric reducer should be used.... FLAT_ON_TOP (FOT) If the suction source is somehow above the pump centerline, then an eccentric reducer can be used (FLAT ON BOTTOM) or a concentric reducer can be used directly on gthe pump suction.

The idea here is to prevent the possibility of developing an air pocket in the suction piping because of the pipe routing.