This picture is reproduced from a Sampson Leffel Turbine Co brochure of about 1910. It shows a naked turbine and the same turbine in a casing. The penstock inlet is facing you, and the casing is sitting on its discharge vent.
Although this Bell casing is not the same as the Tamaiti Co used, it does show clearly how the turbine sits inside a casing (penstock) with the water surrounding all its working parts and how the water, after passing through the turbine, discharges out of the casing.
This illustration shows the unusual characteristic of a Leffel turbine - that the turbine and the wicker gates surrounding it which direct the water flow onto the turbine and control the volume and thus the speed and power, are all immersed in and subject to the flow of in the water through the penstock. This includes the rack and pinion and all the control rods and cranks which work the wicker gates. It is a highly unusual design which would have necessitated good screening of the incoming water to eliminate as much as possible the interference that would be caused by sticks and branches and stones carried by the water. Kaplan and other contemporary turbines had all this apparatus external to the water in the penstock.
These American turbines found a variety of uses in New Zealand's early days of industrialisation, however in a lot of cases I suspect that their consumption of water (they gobbled it) would have made the installation at some locations problematic.