A rotary gear pump moves liquid by using the rotation of meshing gears to trap and transfer fluid through a casing.
Understanding the Basic Principle
Rotary gear pumps are positive displacement pumps, meaning they move a fixed amount of fluid with each rotation. They work by trapping fluid between the teeth of rotating gears and the pump casing, carrying it around from the inlet to the outlet port.
There are two primary types:
- External Gear Pumps: Two identical, intermeshing gears rotating in opposite directions.
- Internal Gear Pumps: An inner gear (rotor) rotating within a larger external gear (idler).
Both types utilize the same core principle of using gear rotation to create moving pockets of fluid.
The Pumping Cycle
The operation of a rotary gear pump involves three main stages:
h3: 1. Fluid Entry (Inlet)
Fluid enters the pump through the inlet port. Based on the specific configuration described, "As the pump operates in a clockwise rotation, the liquid enters the left-hand Inlet Port between the exterior drive gear or rotor and the smaller driven interior gear or idler gear." As the gears rotate away from the inlet port, the space between the gear teeth increases, creating a partial vacuum that draws the liquid into these spaces.
h3: 2. Fluid Transport
The liquid trapped within the pockets formed by the gear teeth and the pump casing is carried around the periphery of the gears. The close clearance between the gears and the casing, as well as between the meshing gears themselves, prevents the fluid from leaking back to the inlet side.
h3: 3. Fluid Discharge (Outlet)
As the gears mesh again near the outlet port, the volume of the pockets is reduced. This action displaces the trapped liquid, forcing it out of the outlet port under pressure. This process happens continuously as the gears rotate, providing a smooth, pulsation-free flow.
Key Components
| Component | Description | Function in Pumping Cycle |
|---|---|---|
| Gears (Rotor/Idler) | Interlocking toothed wheels, typically metal or plastic. | Create moving pockets and displace fluid. |
| Casing | Outer housing enclosing the gears. | Provides a seal for fluid transport. |
| Inlet Port | Opening where fluid enters the pump. | Allows fluid entry as pockets form. |
| Outlet Port | Opening where fluid exits the pump under pressure. | Channels displaced fluid out of the pump. |
| Shaft Seal | Prevents leakage where the drive shaft enters the casing. | Maintains pump integrity. |
| Bearings | Support the rotating shafts/gears. | Ensure smooth rotation and maintain alignment. |
Practical Considerations
- Rotary gear pumps are well-suited for pumping viscous fluids like oils, resins, and paints.
- They provide a constant flow rate proportional to the speed of the gears.
- The close tolerances make them susceptible to damage from abrasive particles, so filtering the fluid is often necessary.
- They are typically used for transferring liquids rather than building high pressures compared to some other pump types.
In summary, a rotary gear pump works by capturing liquid in the spaces between rotating gear teeth at the inlet and carrying it around the casing to the outlet, where the meshing action of the gears pushes the fluid out.
