The interaction of impeller and guide vanes determines the operating behaviour of multistage, high-pressure casing pumps. Especially, the performance curve instability (PCI) is of special interest and is not understood until now. PCI means that the slope of the performance curve becomes positive when the pump works at low volume flow rates (s. Fig. 1 below). 

There are different kind of PCIs. One can differentiate between full load and part load instability. The part load instability is caused by the recirculation region in the entrance of the impeller leading to a head drop. Although this kind of instability is still a problem for impeller pump technology, it is understood and there exist effective means for avoiding this kind of instability. The full load instability – it occurs near the operation of the best efficiency point (BEP) - which is caused by the interaction of the flow at the impeller outlet and entrance of the guide vanes is of more interest and is to be treated in the present intended project because it is not understood and still produces severe problems in impeller pump applications. 

Two new concepts for avoiding the full load instability are examined in this project. The first concept is based on the application of low solidity guide vanes which has been applied for pumping liquid hydrogen and oxygen for rocket propulsion. For this application the full load instability does not occur and the question arises whether this concept can be transferred to classical impeller pumps. The second approach is a combination of a vanless diffusor and a diffusor with classical guide vanes. This idea is mentioned in the newest scientific literature and is to be examined and evaluated in the present intended project.