Water screws can transport very dirty liquids, even when they contain finer solid materials. Usually the conveying height is just a few metres at a relatively fast output-flow rate.

The gear-unit output shaft set at an angle in the helix angle of the screw does not absorb any additional forces and transmits the torque to the screw shaft by means of a flexible coupling. Flender gear units for water screw pumps are configured for such special application. Their use requires of the gear unit an adapted oil level, a suitable shaft sealing, an oil drain and a ventilation device. To prevent the screw from running backwards under the pressure of the water forced back when the motor is stopped, the gear unit can be fitted with a backstop.