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Intake structure Angle

Intake structure Angle

(OP)
We are designing a river water intake structure which comprises 3 x 4.8m wide channels which are separated by 10m high walls.
The river depth varies from 1.3m (dry season) to 6.3m (wet and snow-melt) the river is non tidal and non saline. We don't know how much sediment moves along the river bed or is carried as suspended particles.

So having been doing some reading, for our application where we are on the deep side of a straight section of river, why do all the designs show the entrance as being opened to the flow direction by 45 degrees??

At the moment the 3 channels are all 90 deg to the flow. As we have precious little cover over the pump impeller or intake bell, we have had to put sunken pits to allow the pumps to sit lower without risking air entrainment. (Pump installation in accordance with Hydraulic Institute)

The flow rate in each of the 3 intake channels is 11,250 m3/h so at a 1.3m depth there is the maximum velocity approaching the bar screens of 0.5 m/s.

Are we making a fundamental error by having the intake. Structure at 90 deg rather than 45 deg?

Could anyone out there provide evidence of either case? Perhaps there is no right or wrong way, just depends on the river, etc etc.

RE: Intake structure Angle

Per the 1998 edition of "ANSI/HI 9.8 Pump Intake Design", the intake should be oriented at a 90 degree angle to current flow (see figure, below). I know all of our intakes are designed that way. Don't have the current version of this spec (2012), but doubt that recommendation has changed.
Will you be using traveling screens?

What designs did you see that use a 45 degree orientation?

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Intake structure Angle

(OP)
Sorry for the confusion.... my question was regarding intake structure off take orientation and not pump bay design.

Regards
John

RE: Intake structure Angle

For larger pipe sizes, if the discharge piping is oriented at angle, the access to the pump and suction fittings may be improved. This will tend to increase the size of the pump room as well, but has little effect on the fluid hydraulics.

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