Gear type oil pump from 139QMB scooter engine

A gear pump uses the meshing of

gear A gear or gearwheel is a rotating machine part typically used to transmit rotational motion and/or torque by means of a series of teeth that engage with compatible teeth of another gear or other part. The teeth can be integral saliences or ...

s to

pump A pump is a device that moves fluids (liquids or gases), or sometimes Slurry, slurries, by mechanical action, typically converted from electrical energy into hydraulic or pneumatic energy. Mechanical pumps serve in a wide range of application ...

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 philosophy, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best know ...

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

viscosity Viscosity is a measure of a fluid's rate-dependent drag (physics), resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for e ...

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 provide ''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 An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power gene ...

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 may continuously motion, move and Deformation (physics), deform (''flow'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are M ...

. 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— on 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 Viscosity is a measure of a fluid's rate-dependent resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for example, syrup h ...

fluids. Many variations exist, including helical and

herringbone gear A herringbone gear, a specific type of double helical gear, is a side-to-side, rather than face-to-face, combination of two helical gears of opposite hands. From the top, each helical groove of this gear looks like the letter V, and many togeth ...

sets (instead of spur gears), lobe shaped rotors similar to Roots blowers (commonly used as

superchargers In an internal combustion engine, a supercharger compresses the intake gas, forcing more air into the engine in order to produce more power for a given displacement. It is a form of forced induction that is mechanically powered (usually by a ...

), 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 (turbine), rotor." A gerotor unit consists of an inner and an outer rotor. The inner rotor has ''n'' teeth, while the outer rotor has ''n'' + 1 ...

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

fluids External precision gear pumps are usually limited to maximum working pressures of around and maximum rotation speeds around 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 = pumped volume per rotation × rotational speed *Power = flow rate × pressure *Power in HP ≈ flow rate in US gal/min × (pressure in 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 helps 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. * Aviation: Jet engine fuel pumps

Development

The invention of the gear pump is not uniformly solved. On the one hand, it goes back to Johannes Kepler in 1604; on the other hand,

Gottfried Heinrich Graf zu Pappenheim Gottfried Heinrich Graf zu Pappenheim (29 May 1594 – 17 November 1632) was a German field marshal of the Holy Roman Empire in the Thirty Years' War. A supporter of the Catholic League, he was mortally wounded during the Battle of Lützen ...

is mentioned, who is said to have constructed the capsule blower with two rotating axes for pumping air and water. Pappenheim should have adopted Kepler’s design without mentioning his name.

References

External links