As an external gear coated with special rubber and Viton or Teflon etc .. and the same as an internal gear
External gear pumps are a popular pumping principle and are often used as lubrication pumps in machine tools, in fluid power transfer units, and as oil pumps in engines.

Tne external gear pump is made of MC Nylon, Teflon, PP, or PE are used, the gears don’t easily wear out so that it will last longer.
No noise and vibration when the shaft rotates with high speed.
Little space is required for installation and it is easy to be moved as motor and the pump are directly connected.

Wide range of fluids from the low viscous liquid such as water to the high viscous liquid can be transferred with high pressure.
Chemicals containing sludge and mixture with sands can be also transferred with high speed.
How External Gear Pumps Work
 
External gear pumps are similar in pumping action to internal gear pumps in that two gears come into and out of mesh to produce flow.  However, the external gear pump uses two identical gears rotating against each other -- one gear is driven by a motor and it in turn drives the other gear.  Each gear is supported by a shaft with bearings on both sides of the gear.
1.  As the gears come out of mesh, they create expanding volume on the inlet side of the pump. Liquid flows into the cavity and is trapped by the gear teeth as they rotate.
2.  Liquid travels around the interior of the casing in the pockets between the teeth and the casing -- it does not pass between the gears. 
3.  Finally, the meshing of the gears forces liquid through the outlet port under pressure.
Because the gears are supported on both sides, external gear pumps are quiet-running and are routinely used for high-pressure applications such as hydraulic applications. With no overhung bearing loads, the rotor shaft can't deflect and cause premature wear.