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When gas is introduced into an impeller, it lowers power consumption, as will be described later in more detail. However, in many cases, the power draw increases when flooding, especially for Rushton or other impellers with flat vertical blades. This is due to the loss of gas pockets which streamline flow, illustrated in Chapter 5. This can be used as an indication of flooding, as illustrated in Figure 4.2

However, this phenomenon does not occur at all Froude numbers and can be difficult to detect for deeply concave impellers, as they have little or no gas pockets to streamline flow. For such impellers, the gassing factor is mostly a density reduction factor, which might not change much due to flooding. An opaque vessel will work for this method also.

Figure 4.2 Impeller flooding by power draw.