The main difference of these pumps' design compared with the gear pump is the presence of big teeth and big cavities in the gears. The pitch of big teeth and big cavities is greater than the pitch of small teeth in 3, 5, 7 or more times. Besides, the addendum diameter of big teeth is greater than the addendum diameter of small teeth. This simple change in the gear pump design gives the following advantages:

Higher suction lift and ability to deliver high viscous liquids at higher RPM, because high volume of the pocket between two opposite big teeth generates high vacuum at the suction port enabling speed increase when delivering viscous liquids compared with the same liquid pumped by gear pump, thus increasing productivity.

High volumetric efficiency, since gears have high number of small teeth (rated) and high engagement factor consequently, which improves meshing hermeticity.

High hydraulic-mechanical efficiency, because a great part of the liquid is discharged as a result of constantly diminishing large pocket as apposed with tooth engagement of one gear into cavity of the other gear in case of the gear pump. Thus the pumps have lower pulsation.

Long life operation and high reliability, because of the small meshing circumferential force, which results low friction forces between teeth, low contact fatigue and consequently less wear. Besides, high engagement factor enhances smooth operation and thus contributes to reliability too.

The other great advantage of this pump is the possibility to make driven gear from plastics, such as polyamide and POM again because of the small meshing circumferential force. It is possible to generate up to 200 Bar liquid pressure with plastic driven gear.
The metal to plastic gears meshing provides the following advantages:
Sufficient hermeticity to carry low viscous liquids like water at higher pressure.
The pump can handle suspended solids or abrasives.
Low noise
Low cost