This design concept could be applied for connecting a straight pipe or tunnel with a vertical shaft, but unlike the normal Tee-junction, the flows are turned by the shape of the junction (represented by the above diagram’s thick black lines) to meet at 120 degrees to each other and so there should be no efficiency bias in favour of horizontal flow through the junction, even for fast flow.
The diffusers (illustrated by diagram’s red lines) should be custom designed to decelerate flow into the junction and accelerate flow out of the junction, by converting in flow velocity head to slower, higher pressure flow around the curves and then from higher pressure back to outflow velocity head once again.
Total diffuser and bend velocity head loss may not be significant in situations such as high head hydroelectricity tunnels where the velocity head (of a metre or two) is small compared to the hydrostatic head (hundreds of metres) so losing 1m or so of head is negligible in the grand scheme of things.
Scottish Scientist 
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