Gear pumps – definition, function and characteristics

Definition

A gear pump is a type of volumetric pump that uses gear meshing to convey liquids and belongs to a category of rotary pumps. Its basic structure consists of a pair of intermeshing gears (the driving gear and the driven gear), the pump body, front and rear end covers, etc. When the gears rotate, the liquid is drawn into the meshing chamber and is then pushed to the outlet end as the gears rotate.

Function

Gear pumps are mainly used for:
Transporting liquids: such as lubricating oil, hydraulic oil, fuel, polymers and other low-viscosity or medium-viscosity liquids.
Providing stable flow: suitable for hydraulic systems or lubrication systems that require a constant flow (without pulsation).
Pressurizing: providing pressurized oil in hydraulic systems to drive actuators (such as hydraulic cylinders, motors).

Characteristics

(1) Advantages

Simple structure, few parts, low manufacturing and maintenance costs.
Small size, light weight, suitable for restricted spaces.
Strong self-priming ability, no need to pump in advance during startup (but dry running may damage the seal).
Stable flow, small output pulsation (external meshing gear pump has slightly larger pulsation, internal meshing is more stable).
Resistant to contamination, capable of transporting liquids containing tiny particles (but high-mobility particles will still reduce lifespan).
Suitable for high rotational speeds, can be directly connected to the motor, without the need for a reduction device.

(2) Disadvantages

Not suitable for transporting high-viscosity liquids (such as heavy oil and asphalt), efficiency will significantly decrease.
There is a phenomenon of trapped oil (in external meshing gear pumps), which may cause noise and vibration. Load relief grooves need to be designed to alleviate this issue.
Efficiency decreases after wear, and wear of gears and side plates will lead to an increase in internal leakage.
Pressure is limited, with the general working pressure being ≤ 20 MPa (for high pressure, multiple stages or special design are required).
It cannot be variable; the flow rate is determined by the rotational speed, and regulation requires variable-speed drive.

Main types

External meshing gear pump: The most common type, two gears mesh externally, simple structure but with significant pulsation.
Internal meshing gear pump (such as cycloidal gear pump): Low noise, stable flow, suitable for precision hydraulic systems.
Interlocking gear pump: Can counteract axial force, reduce bearing load, but the manufacturing process is complex.

Typical applications

Hydraulic systems (machinery, construction equipment)
Fuel delivery (automobiles, aviation)
Lubrication systems (engines, gearboxes)
Chemical processes (transportation of resins, solvents, etc.)