Degree of reaction
The degree of reaction (rth), or reaction ratio, is a parameter used for multistage turbomachinery defining the ratio of the static head (see Clearance gap pressure) to the fall head (of turbines) or the pump head (of centrifugal pumps). It is an indication of how the static pressure is distributed between impeller and stage. A degree of reaction of zero means that there is no increase in pressure within the impeller (constant pressure impeller), whereas a degree of reaction of 1 means that the static pressure increase in the stage takes place solely in the impeller.
The degree of reaction can be calculated from the velocity triangles of an impeller element (see fundamental equation under Fluid mechanics) and is given by:
Typical degrees of reaction of centrifugal pumps vary between 0.5 and 1, and can in exceptional cases also be above 1, for example for propeller pumps.
