What is a Gear Pump?

A sump pump uses a gear pump to move water.

A gear pump is a mechanical pump that moves liquids through two rotating gears. The liquid flows under pressure from the pump inlet to the discharge in the space formed by the gear teeth. The liquid also serves to lubricate the gears. The small gaps between the pump chamber walls and the gear teeth create a tight seal, thus preventing liquid from flowing back through the inlet. Unlike other types of pumps, gear pumps do not need to be primed and can run dry for short periods without damaging the pump. They are typically used to pump water, oil and other liquids.

Gear pumps are capable of producing very high internal pressures and are often used to pump thick liquids such as pitch and crude oil.

Gear pumps are capable of producing very high internal pressures and are often used to pump thick liquids such as pitch and crude oil. Pump speeds should be reduced as the viscosity increases to allow sufficient time for the liquid to fill the voids between the gear teeth. A gear pump is capable of pumping very precise amounts of liquid at high pressure and is often used to pump fuel and heating oil, diesel oil and gasoline. Gear pumps are commonly used in automotive oil pumps as well as domestic sump pumps.

A gear pump works on the principle of displacement. As the gears rotate within the gear pump chamber, they create areas of low and high pressure. An area of ​​low pressure, or vacuum, is created between the teeth of the gears as they come loose. Liquid flows into this lower pressure area. As the gear continues to rotate, liquid is trapped in the pocket formed by the gear teeth and the wall of the pump chamber. Finally, an area of ​​increased pressure is created as the gears begin to mesh, forcing fluid from the gear teeth to the discharge outlet. Extremely small clearances between the gear teeth and the wall are required for the pump to work effectively. Over time, the gear pump will gradually lose efficiency as clearances increase due to normal wear and tear.

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There are two main types of gear pumps, internal and external. The internal gear pump, also known as a gerotor, has two gears. A smaller inner gear fits inside a larger one and both rotate in the same direction. The smaller gear always has one less tooth than the larger gear and is mounted off-center to the axis of the larger gear. This allows the inner gear to rotate freely within the outer gear, while providing the space needed to pump liquid from inlet to gear pump discharge. Power is applied to the inner gear shaft, which then drives the outer gear.

External gear pumps have two identical gears that rotate in opposite directions. Liquid is transported in the space created between the gear teeth and the sides of the pump chamber. Power is applied to the drive gear shaft, which in turn drives the other gear. Spur gears are generally used in external gear pumps, although helical and herringbone gears are sometimes used when excessive pump noise is a concern.

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