External%20Gears

1
External Gears

• Dinesh Bakthavatsalam
• 20192297
• 4M-I
• September 30th , 2005

2
External Pumps Overview

• External gear pumps are a popular pumping
  principle and are often found in lubrication
  pumps in machine tools, in fluid power transfer
  units, and as oil pumps in engines
• External gear pumps can come in single or double
  (shown, left) pump configurations with spur,
  helical, and herringbone gears
• Small external gear pumps usually operate at 1750
  or 3450 rpm and larger models operate at speeds
  up to 640 rpm.
• Reduced speeds with high-viscosity liquids
  results in greater efficiency.
• The design of external gear pumps allows them to
  be made to close tolerances.
• Tighter internal clearances provide for a more
  reliable measure of liquid passing through a pump
  and for greater flow control.

3
How External Gear Pumps Work

• The external gear pump uses two identical gears
  rotating against each other
• One gear is driven by a motor and it in turn
  drives the other gear.
• Liquid flows into the cavity and is trapped by
  the gear teeth as they rotate.
• Liquid travels around the interior of the casing
  in the pockets between the teeth and the casing
• Finally, the meshing of the gears forces liquid
  through the outlet port under pressure.

4
Advantages Disadvantages

• ADVANTAGES
• High speed.
• Medium pressure.
• No overhung bearing loads.
• Relatively quiet operation.
• Design accommodates wide variety of materials.

• DISADVANTAGES
• Four bushings in liquid area.
• No solids allowed.
• Fixed End Clearances.

5
Applications

• Industrial and mobile applications
• Fuel and lubrication
• Metering
• Mixing and blending (double pump)
• Hydraulic applications
• OEM configurations
• Precise metering applications
• Low-volume transfers
• Light or medium duty

6
Materials of Construction

• Externals (head, casing, bracket) - Iron, ductile
  iron, steel, stainless steel.
• Internals (rotor, idler) - Steel, stainless
  steel.
• Bushing - Carbon, bronze, silicon carbide.
• Shaft Seal - Packing, lip seal, component
  mechanical seal, magnetically-driven pump.

7

• Sources
• www.wikepedia.com
• www.pumpschool.com/principles/external.htm