Gear type oil pump from 139QMB scooter engine

A gear pump uses the meshing of

gear A gear is a rotating circular machine part having cut teeth or, in the case of a cogwheel or gearwheel, inserted teeth (called ''cogs''), which mesh with another (compatible) toothed part to transmit (convert) torque and speed. The basic ...

s to

pump A pump is a device that moves fluids (liquids or gases), or sometimes slurries, by mechanical action, typically converted from electrical energy into hydraulic energy. Pumps can be classified into three major groups according to the method they ...

fluid by displacement. They are one of the most common types of pumps for hydraulic fluid power applications. The gear pump was invented around 1600 by

Johannes Kepler Johannes Kepler (; ; 27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws ...

. Gear pumps are also widely used in chemical installations to pump high

viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the int ...

fluids. There are two main variations: ''external gear pumps'' which use two external spur gears, and ''internal gear pumps'' which use an external and an internal spur gear (internal spur gear teeth face inwards, see below). Gear pumps are ''positive displacement'' (or ''fixed displacement''), meaning they pump a constant amount of fluid for each revolution. Some gear pumps are designed to function as either a motor or a pump.

Theory of operation

As the gears rotate they separate on the intake side of the pump, creating a void and suction which is filled by

fluid In physics, a fluid is a liquid, gas, or other material that continuously deforms (''flows'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are substances which cannot resist any shear ...

. The fluid is carried by the gears to the discharge side of the pump, where the meshing of the gears displaces the fluid. The mechanical clearances are small— in the order of 10 μm. The tight clearances, along with the speed of rotation, effectively prevent the fluid from leaking backwards. The rigid design of the gears and houses allow for very high pressures and the ability to pump highly

viscous The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity quantifies the in ...

fluids. Many variations exist, including helical and herringbone gear sets (instead of spur gears), lobe shaped rotors similar to Roots blowers (commonly used as superchargers), and mechanical designs that allow the stacking of pumps. The most common variations are shown below (the drive gear is shown blue and the idler is shown purple). File:Gear pump.png, External gear pump design for hydraulic power applications. File:Gear pump 2.png, Internal gear (

Gerotor A gerotor is a positive displacement pump. The name ''gerotor'' is derived from "generated rotor". A gerotor unit consists of an inner and outer rotor. The inner rotor has ''n'' teeth, while the outer rotor has ''n''+1 teeth; with ''n'' defined a ...

) pump design for automotive oil pumps. File:Gear pump 3.png, Internal gear (Crescent Internal Gear) pump design for high

fluids. An external precision gear pump is usually limited to a maximum working pressure of and a maximum speed of 3,000 rpm. Some manufacturers produce gear pumps with higher working pressures and speeds but these types of pumps tend to be noisy and special precautions may have to be made.Pinches, M J (2000). ''Kempe's Engineers Year-Book'', p. 2070. Miller Freeman, Kent. . Suction and pressure ports need to interface where the gears mesh (shown as dim gray lines in the internal pump images). Some internal gear pumps have an additional, crescent-shaped seal (shown above, right). This crescent functions to keep the gears separated and also reduces eddy currents. Pump formulas: *Flow rate in US gal/min = Pump Capacity × rpm *Power in hp = US gal/min × (lbf/in²)/1714

Efficiency

Gear pumps are generally very efficient, especially in high pressure applications.

Factors affecting efficiency

* Clearances: Geometric clearances at the end and outer diameter of the gears allows leakage and back flow. However sometimes higher clearances help reduce hydrodynamic friction and improve efficiency. * Gear backlash: High backlash between gears also allows fluid leakage. However, this aides to reduce wasted energy from trapping the fluid between gear teeth (known as pressure trapping).

Applications

* Petrochemicals: Pure or filled bitumen, pitch, diesel oil, crude oil, lube oil etc. * Chemicals: Sodium silicate, acids, plastics, mixed chemicals, isocyanates etc. * Paint and ink. * Resins and adhesives. * Pulp and paper: acid, soap, lye, black liquor, kaolin, lime, latex, sludge etc. * Food: Chocolate, cacao butter, fillers, sugar, vegetable fats and oils, molasses, animal food etc.

References

External links