Blackmer offers a range of internal gear pumps ideally suited for applications where high- or wide-ranging viscosities are prevalent. Internal gear pumps operate on the “gear within a gear” principle. Liquid enters the suction port between the teeth of the rotor gear (the larger exterior driven gear) and the idler gear (the smaller interior gear). As the internal gear pump rotates to suction the teeth of the gears come out of mesh, an atmospheric vacuum or low-pressure zone is created at the suction port, pulling liquid into the spaces.