This is a modification of a regular Gear
Pump and all the variations in that pump (number of teeth, size, shape, etc.)
are possible here too.
The tubing around the edges of this pump returns pressure
-- not liquid -- to opposite sides of the shafts. Very little fluid is transferred
anywhere by these extra tubes.
By equalizing pressure on each side of the
shafts, friction and wear are both reduced in comparison to the standard gear
Other types of pumps, such as Vane
Pumps, sometimes are balanced in similar ways.