Abstract: A positive displacement rotary pump with an improved impeller design integrating a replaceable wiper insert. The impeller generally has or more lobes and an equal number of conjugate surfaces. Each lobe has a cavity which holds a wiper blade. The wiper blade improves efficiency by making a seal with a pump chamber or the conjugate surface on the other impeller as it rotates. The wiper is pressed radially outward from a central axis of the impeller by a biasing means such as a spring.