For truck-mounted hydraulic systems, the most typical design in use is the gear pump. This design is characterized 
as having fewer shifting parts, being easy to service, more tolerant of contamination than additional designs and fairly inexpensive. Gear pumps are fixed displacement, also called positive displacement, pumps. This means the same level of circulation is created with each rotation of the pump’s shaft. Gear pumps are rated when it comes to the pump’s maximum pressure rating, cubic ” displacement and maximum input speed limitation.
Generally, gear pumps are found in open center hydraulic systems. Gear pumps trap oil in the areas between your teeth of the pump’s two gears and the body of the pump, transport it around the circumference of the gear cavity and then push it through the wall plug port as the gears mesh. Behind the brass alloy thrust plates, or use plates, a little amount of pressurized essential oil pushes the plates tightly against the apparatus ends to improve pump efficiency.