Internal External Gear Pump

By Andrew McKinney

External Gear Pump Internal Gear Pump

Objective: Compare the two pumps

External Gear Pump

• Been around since the beginning oil pump industry • Used for high pressure applications (pulse free fluid flow) • Smaller - operate at 1 750 rpm or 3 450 rpm • Larger operate 640 rpm • Can handle viscous and water type liquids well • Thick liquids speed must be properly set (small meshing time) •True involute gear form (contour gear curved)

Internal Gear Pump

• Crescent pump • Less than 100 years old • Generally run at 1 150 rpm • Smaller ones run at 3 450 rpm (same as external) • Fairly long meshing time (allowing higher speeds with thicker fluids than external) •Not true involute gear form •$$$

Materials

• Metals of various types and hardness through to plastics of various types and hardness • Metal allow for high temperatures and aggressive products

Internal External Abrasives Thin liquids Good Poor Pump Handling Comparison Good Good Viscous Excellent Good Solids Dry Poor Poor Difference in Pressure Average Average

Stack Up

• Internal pump, more modern pump • Both have a pulse free fluid flow • External pump, cheaper • External pump has to run slower with thicker fluids • External involute form allows for less wear and tear • Internal pump handles abrasive and viscous fluids a lot better

References

• • • •

http://www.pumpschool.com/principles/external.htm

http://www.appliedpumps.co.uk/Gear%20Pump%20Overview.ht

m http://www.bin95.com/ebooks/pump_types_ebook.htm

http://www.pumpschool.com/intro/selection.htm