CETIM has decided to modify its hydraulic test platform to accommodate very large vertical pumps. For more than 30 years, CETIM (Centre Technique des Industries Mécaniques) has operated a platform for testing hydraulic equipment (pumps, turbines, valves) in Nantes, France. This platform was developed at the request of French manufacturers but now also provides services for manufacturers further afield such as Alstom, Flowserve, KSB, Sulzer. The platform equipment was first sized to test machines under conditions up to 4000 kVA, 250 bar and 20,000 m3/h. At the request of Alstom Fluides et Mécanique (AFEM), it was decided to raise the pump suction capacity of the Nantes test platform to 35 000 m3/h within a 10-metre deep well in order to determine the hydraulic characteristics of large vertical pumps (including their submergence) under suitable conditions. In order to ensure that the operating limits of the well were suitable, CETIM has requested Alstom CERG (Centre d’Etudes et de Recherches de Grenoble) to build an equivalent small-scale model. Simultaneously, CETIM’s Fluid & Flow Technologies Department has performed a numerical modelling.