Useful Information On Gear Pumps
Useful information on Gear Pumps
By michael-smith-engineers.co.uk
What is a gear pump?
A gear pump is a type of positive displacement (PD) pump. It moves a fluid by repeatedly enclosing a fixed volume using interlocking cogs or gears, transferring it mechanically using a cyclic pumping action. It delivers a smooth pulse-free flow proportional to the rotational speed of its gears.
How does a gear pump work?
Gear pumps use the actions of rotating cogs or gears to transfer fluids. The rotating element develops a liquid seal with the pump casing and creates suction at the pump inlet. Fluid, drawn into the pump, is enclosed within the cavities of its rotating gears and transferred to the discharge. There are two basic designs of gear pump: external and internal (Figure 1).
External Gear Pump
An external gear pump consists of two identical, interlocking gears supported by separate shafts. Generally, one gear is driven by a motor and this drives the other gear (the idler). In some cases, both shafts may be driven by motors. The shafts are supported by bearings on each side of the casing.
As the gears come out of mesh on the inlet side of the pump, they create an expanded volume. Liquid flows into the cavities and is trapped by the gear teeth as the gears continue to rotate against the pump casing.
The trapped fluid is moved from the inlet, to the discharge, around the casing.
As the teeth of the gears become interlocked on the discharge side of the pump, the volume is reduced and the fluid is forced out under pressure.
No fluid is transferred back through the centre, between the gears, because they are interlocked. Close tolerances between the gears and the casing allow the pump to develop suction at the inlet and prevent fluid from leaking back from the discharge side (although leakage is more likely with low viscosity liquids).
External gear pump designs can utilise spur, helical or herringbone gears.
Internal gear pump
An internal gear pump operates on the same principle but the two interlocking gears are of different sizes with one rotating inside the other. The larger gear (the rotor) is an internal gear i.e. it has the teeth projecting on the inside. Within this is a smaller external gear (the idler – only the rotor is driven) mounted off-centre. This is designed to interlock with the rotor such that the gear teeth engage at one point. A pinion and bushing attached to the pump casing holds the idler in position. A fixed crescent-shaped partition or spacer fills the void created by the off-centre mounting position of the idler and acts as a seal between the inlet and outlet ports.
As the gears come out of mesh on the inlet side of the pump, they create an expanded volume. Liquid flows into the cavities and is trapped by the gear teeth as the gears continue to rotate against the pump casing and partition.
The trapped fluid is moved from the inlet, to the discharge, around the casing.
As the teeth of the gears become interlocked on the discharge side of the pump, the volume is reduced and the fluid is forced out under pressure.
Internal gear pump designs only use spur gears.
Chemical mixing and blending
Acids and caustic (stainless steel or composite construction) Alcohols and solvents Asphalt, bitumen, and tar
Food products: corn syrup, peanut butter, cacao butter, chocolate, sugar, fillers, vegetable fats, vegetable oils, animal feed
Soaps and surfactants
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| Chemical mixing and blending | | |
| Acids and caustic (stainless steel or composite construction) | | |
| Alcohols and solvents | | |
| Asphalt, bitumen, and tar | | |
| Food products: corn syrup, peanut butter, cacao butter, chocolate, sugar, fillers, vegetable fats, vegetable oils, animal feed | | |
| Soaps and surfactants | |
Summary
A gear pump moves a fluid by repeatedly enclosing a fixed volume within interlocking cogs or gears, transferring it mechanically to deliver a smooth pulse-free flow proportional to the rotational speed of its gears. There are two basic types: external and internal. An external gear pump consists of two identical, interlocking gears supported by separate shafts. An internal gear pump has two interlocking gears of different sizes with one rotating inside the other.
Gear pumps are commonly used for pumping high viscosity fluids such as oil, paints, resins or foodstuffs. They are also preferred in applications where accurate dosing or high pressure output is required. External gear pumps are capable of sustaining higher pressures (up to 7500 psi) whereas internal gear pumps have better suction capabilities and are more suited to high viscosity and shear-sensitive fluids.