External gear pumps are typically used as lubrication pumps in machine tools, oil pumps in engines and in fluid power transfer units. They can have one or two gears in the pump that drives the liquid. As with all gear pumps, external gear pumps provide a relatively smooth flow of liquid. The two-gear versions of external gear pumps differ from internal gear pumps in that they have two identically sized gears operating next to each other. One gear connected by a drive shaft to a motor, drives the second gear. As the gears unmesh, they create a vacuum that draws in the liquid from an inlet valve. The gears carry the liquid around the casing until they begin to mesh again, forcing the liquid through the outlet valve.
External gear pumps run with close tolerances, allowing them to pump to pressures beyond 3,000 PSI / 200 BAR, making them well suited for hydraulic systems. Their tight internal clearances also provide a more reliable measure of liquid passing through a pump and greater flow control, making them a pump of choice for precise transfer and metering applications requiring the flow of fuels, chemical additives and polymers.