Gear pump

<h2 id="theory-of-operation">Theory of operation</h2>
<p>As the gears rotate they separate on the intake side of the pump, creating a void and suction which is filled by <a href="/facts/Fluid/tMQ46Tmz">fluid</a>.  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.
</p><p>The rigid design of the gears and houses allow for very high pressures and the ability to pump highly <a href="/facts/Viscosity/QLVfrdCz">viscous</a> fluids.
</p><p>Many variations exist, including helical and <a href="/facts/Herringbone_gear/MIFsLmlM">herringbone gear</a> sets (instead of spur gears), lobe shaped rotors similar to <a href="/facts/Roots_type_supercharger/1AY0n9Pc">Roots blowers</a> (commonly used as <a href="/facts/Superchargers/gvEtspvw">superchargers</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).
</p>

<p>External precision gear pumps are usually limited to maximum working pressures of around 210 bars (21,000 kPa) 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.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a>
</p><p>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.
</p><p>Pump formulas: 
</p>
<ul><li>Flow rate = pumped volume per rotation × rotational speed</li>
<li>Power = flow rate × pressure</li>
<li>Power in HP ≈ flow rate in US gal/min × (pressure in lbf/in2)/1714</li></ul>
<h2 id="efficiency">Efficiency</h2>
<p>Gear pumps are generally very efficient, especially in high-pressure applications.
</p><p>Factors affecting efficiency:
</p>
<ul><li>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.</li>
<li>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).</li></ul>
<h2 id="applications">Applications</h2>
<ul><li>Petrochemicals: Pure or filled bitumen, pitch, diesel oil, crude oil, lube oil etc.</li>
<li>Chemicals: Sodium silicate, acids, plastics, mixed chemicals, isocyanates etc.</li>
<li>Paint and ink</li>
<li>Resins and adhesives</li>
<li>Pulp and paper: acid, soap, lye, black liquor, kaolin, lime, latex, sludge etc.</li>
<li>Food: Chocolate, cacao butter, fillers, sugar, vegetable fats and oils, molasses, animal food etc.</li>
<li>Aviation: Jet engine fuel pumps</li></ul>
<h2 id="development">Development</h2>
<p>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, <a href="/facts/Gottfried_Heinrich_Graf_zu_Pappenheim/lpvdpFv6">Gottfried Heinrich Graf zu Pappenheim</a> 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.
</p>
<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Gerotor/cE2LwWwj">Gerotor</a></li>
<li><a href="/facts/Hydraulic_pump/EVxec5gu">Hydraulic pump</a></li>
<li><a href="/facts/Vane_pump/E9QScV9L">Vane pump</a></li></ul>

<h2 id="external-links">External links</h2>

Wikimedia Commons has media related to Gear pump.

<ul><li><a href="https://pumpschool.com/principles/external.php">External gear pump description</a></li>
<li><a href="https://pumpschool.com/principles/internal.php">Internal gear pump description</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>"Welcome to the Hydraulic Institute". Pumps.org. Archived from the original on 2013-06-26. Retrieved 2013-08-18. <a href="https://web.archive.org/web/20130626081952/http://www.pumps.org/content_detail_pumps.aspx?id=1772" target="_blank">https://web.archive.org/web/20130626081952/http://www.pumps.org/content_detail_pumps.aspx?id=1772</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Frank Prager,
Kepler as inventor,
Vistas in Astronomy,
Volume 18,
1975,
Pages 887-889,
https://doi.org/10.1016/0083-6656(75)90184-1. <a href="https://doi.org/10.1016/0083-6656(75)90184-1" target="_blank">https://doi.org/10.1016/0083-6656(75)90184-1</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Pinches, M J (2000). Kempe's Engineers Year-Book, p. 2070. Miller Freeman, Kent. ISBN 0863824420. <a href="/wiki/ISBN_(identifier)" target="_blank">/wiki/ISBN_(identifier)</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
</ol>

Gear pump open-in-new

Gear pump