To be used when we are dealing with a flow rate with a range of up to 3m cubic / sec. and with jumps under 1.5 m
It is the only technology that can turn these jumps of limited height, in energy enabling an efficiency up to 60% to which must be added the returns procured by the transmission, by the generator and the electrical parts
It is the oldest type of vertical wheel with a type of rotation generated through the leverage produced by the water on the blades of the bottom of the wheel. For this reason, these types get little benefit from the jump and are better suited to shallow streams in plain.
This type of wheel always requires limited civil works and is housed in the channel, equipped by a safety grid of 15/20 cm. and a compartment for the electrical panels. As all wheels, to vary the flow rate is not necessary to make adjustments, and produces a virtually constant efficiency up to 20% of the design flow rate
There are also three variants of this wheel which take their name by those who have designed them: the Poncelet wheel, the Sagebien wheel and the Zuppinger wheel.
The main advantages for the use of these wheels concern the fact that they are a little less expensive than other types, simpler to build, and have less environmental impact, since it does not create large changes to the river
The disadvantages relate instead, of the one part a lower efficiency as they generate less energy and the other part is that these wheels can only be used when the flow rate can provide a sufficient torque.
The undershot wheels are also suitable for installation on floating platforms sometimes installed immediately downstream of bridges or where the flow restriction increases the speed of the current.