Gear pumps use rotating gears to move liquids, creating high pressure and an airtight seal. They are used for water, oil, and thick liquids. The displacement principle creates low and high pressure areas, and there are two types of gear pumps: internal and external.
A gear pump is a mechanical pump that moves liquids by the use of two rotating gears. The liquid flows under pressure from the pump inlet to the outlet in the space formed by the gear teeth. The liquid also serves to lubricate the gears. Small gaps between the pump chamber walls and the gear teeth create an airtight 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. Pump speeds must be reduced as viscosity increases to allow the liquid to fill the gaps between the gear teeth long enough. A gear pump is capable of pumping very precise quantities of liquid under high pressure and is often used to pump fuel and heating oil, diesel and petrol. Gear pumps are also commonly used in automobile oil pumps and household sump pumps.
A gear pump works according to the displacement principle. As the gears rotate within the gear pump chamber, they create areas of low and high pressure. A low pressure area, or vacuum, is created between the gear teeth when they are not meshing. The liquid flows into this area of lower pressure. As the gear continues to rotate, liquid becomes trapped in the pocket formed by the gear teeth and the pump chamber wall. Finally, once the gears begin to mesh, an area of increased pressure is created, forcing the liquid from the gear teeth to the discharge outlet. Extremely small clearances are required between the gear teeth and the wall for the pump to operate effectively. Over time, the gear pump will gradually lose efficiency as clearances increase due to normal wear.
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 internal gear fits inside a larger one and both rotate in the same direction. The smaller gear always has one tooth less than the larger one and is mounted off center to the shaft of the larger gear. This allows the internal gear to rotate freely within the external gear, while providing the clearance needed to pump the liquid from the gear pump’s suction to discharge. Power is applied to the shaft of the inner gear, which then drives the outer gear.
External gear pumps have two identical gears that rotate in opposite directions. The liquid is transported in the space created between the gear teeth and the walls of the pump chamber. Power is applied to the shaft of the drive gear, which in turn drives the other gear. Spur gears are usually used in external gear pumps, although helical and herringbone gears are sometimes used when excessive pump noise is a problem.
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