Introduction
There are two common centrifugal pump designs employed today:
- Overhung centrifugal pump.
- Between bearings centrifugal pump.
A between bearings centrifugal pump uses one or several impellers installed on a shaft that is suspended at both ends between two bearings.
An overhung centrifugal pump uses one impeller installed on a shaft that is suspended at one end by bearings.
Between bearing centrifugal pumps are favoured over overhung centrifugal pumps whenever higher flow rates, higher pressures, and heavier loading of the pump will occur.
The main disadvantage of an overhung pump compared to a between bearing’s pump, is that the overhung design supports the shaft on only one side of the impeller, whereas the between bearings pump design supports the pump shaft on both sides of the impeller. The additional mechanical support from the bearings, and the ability to more effectively balance the loads acting on the pump (axial loads mostly), are the main reasons for favouring a between bearings pump for more severe and challenging applications.
Please see our overhung centrifugal pumps and net positive suction head and cavitation articles if you would like to learn more about this topic.
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Between Bearings Centrifugal Pump Components
A between bearings centrifugal pump will have some of the following components depending upon its design:
- Impeller – the centrepiece of the pump. The impeller converts the kinetic energy of the fluid to pressure energy. Centrifugal pump impellers are classified as open, semi-open, or closed.
- Volute casing – surrounds the impeller. Fluid is discharged from the impeller to the volute casing. The volute casing is designed to convert more kinetic energy to pressure energy.
- Diffuser – an additional ring-shaped item surrounding the impeller(s). Like the volute casing, diffusers convert kinetic energy to pressure energy, but diffusers are smaller and require less space. For this reason, multistage centrifugal pumps use diffusers, not volute casings.
- Pump Shaft – a cylindrical shaped piece of metal installed along the centre-axis of the pump. Bearings, shaft keys, impellers, mechanical seals or packing, are all installed around or onto the pump shaft.
- Driver – the item providing the rotary motion to the pump. Common drivers include electric motors, steam turbines, and hydraulic turbines.
- Compression Packing (‘packing’) – a rough rope-like material used to seal the space between the pump casing and shaft. The packing material is installed within a stuffing box; the material may or may not be lubricated from an external source.
- Lantern Ring – if packing material is lubricated from an external source, a lantern ring makes this possible; lantern rings are located within the stuffing box.
- Mechanical Seal – used to seal the space between the pump casing and shaft. The alternative to a mechanical seal is compression packing (both serve the same purpose).
- Bearings – used to cater for the axial and radial loads generated by the pump when stationary and in service. Centrifugal pumps use anti-friction bearings (roller bearings) e.g. single row ball bearings (Conrad bearings) or double row ball bearings.
Additional Resources
https://en.wikipedia.org/wiki/Centrifugal_pump
https://www.powerzone.com/resources/glossary/centrifugal-pump
https://www.introtopumps.com/pumps-101/what-is-a-centrifugal-pump