How External Gear Pumps Work
External gear pumps generate a pumping action by using two gears that come into and out of mesh to produce flow. The external gear pump uses two identical gears rotating against each other -- a motor drives one gear and it in turn drives the other gear. A shaft supports each gear with bearings on both sides of the gear.
- As the gears come out of mesh, they create expanding volume on the inlet side of the pump. 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 -- it does not pass between the gears.
- Finally, the meshing of the gears forces liquid through the outlet port under pressure. Because the gears are supported on both sides, external gear pumps are quiet running and are routinely used for high-pressure applications such as hydraulic applications. With no overhung bearing loads, the rotor shaft can't deflect and cause premature wear.
The Macropaver uses an external gear pump as its standard emulsion pump to handle both standard and polymer modified emulsions. The external gear pump is a reliable fixed displacement pump that is not affected by polymers or latex used in microsurfacing emulsions. Having a fixed displacement that does not change is critical to the emulsion-to-aggregate ratio when mixing slurry seal and microsurfacing.
2. Are all gear pumps the same?
No. The gapping in gear pumps depends on the design, the speed depends on the sizing. This is what exerts shear. This for emulsions needs to be minimized. Gear pump designers do this. The WRONG gear pump will cause problems.
3. What effect does this have on emulsions?
Emulsions are dispersions of electrically stabilized particles of asphalt. If they are OVER sheared then they can be squeezed together to form larger particles and ultimately break the emulsion.
The coarser the emulsion is initially the worse this effect.
As emulsion equipment manufacturers and designers of products we make fine emulsions. Not just to ensure easy handling but to optimize performance.
A coarse emulsion may break in a gear pump. But it will also have worse field performance in
- Adhesion
- Cohesion
- Waterproofing and coating
- Abrasion resistance
- Life under traffic
If you visit our web site www.slurry.com you will find detailed papers and presentations that demonstrate this.
Correct emulsion will NOT break in the CORRECT gear pump.
4. How do we know it works?
VSS is the largest slurry and microsurfacing contractor in California- the biggest market in USA. VSS is the biggest emulsion producer in the biggest market in USA.
WE have used these pumps on MP for more than 25 years.
USA is the biggest market in the world.
We also have a CD-Rom showing the data referred to above.
Glynn Holleran
January 18, 2001