Centrifugal pumps have a place in many industrial applications and are often considered one of the integral gears that keep the world moving!
The first true centrifugal pump was developed by French-born inventor Denis Papin in 1687. This pioneering pump used straight vanes to propel water. Since then, the centrifugal pump has undergone a variety of changes in mechanisms, size, and design to become more efficient and effective at displacing fluid.
Centrifugal Pumps and How They Work
A centrifugal pump is a hydraulic machine that displaces fluid by transferring energy from a rotating component, the impeller, to the fluid itself. It creates a motion, known as a forced vortex flow, which increases the fluid’s pressure head, resulting in the movement of water from one point to another. Centrifugal pumps are also energy conversion machines that change the fluid’s energy from kinetic energy to pressure energy, causing the fluid to flow, usually in an upward direction. Centrifugal pumps are therefore used to raise fluids from a lower level to a higher one.
The centrifugal pump has two ports – one is the inlet and the other is the outlet. The inlet runs through the center of the pump on its horizontal axis, while the outlet is positioned on its vertical axis. The inlet is also called the suction line, while the outlet is referred to as the discharge line.
Apart from the impeller, centrifugal pumps also have another important component- the casing (volute). This is a pressure containment vessel that seals off the inside of the pump from atmospheric pressure and directs the fluid into the impeller.
When the pump is switched on, the impeller begins to spin, creating a low pressure suction at the inlet. This, in turn, pulls the fluid into the center of the impeller. Once the fluid comes into contact with the rotating impeller, it is pushed outwards onto the casing and onward to the outlet. This motion is caused by centrifugal forces.
Basic Parts of a Centrifugal Pump
The centrifugal pump is divided into two major parts – the wet end and the mechanical end. All its components are categorized based on which of these two parts they are found.
The impeller and casing together make up the wet end of the centrifugal pump. The mechanical end comprises those parts within the casing that support the impeller, namely the shaft, sealing, and bearings.
- The casing (volute) is a pressure containment vessel that directs the fluid’s movement into and out of the centrifugal pump.
- The impeller is a rotor whose role is to increase the pressure and flow of a fluid.
- Shaft (bearings): They are responsible for preventing the leakage of the pumped liquid inside the pump and are distributed throughout the internal configuration.
- The Shaft (rotor) acts as a support for the impeller, as the impeller is mounted on the shaft. It is responsible for transmitting torque to the impeller from the motor.
- Bearings restrict the movement of the shaft rotor and decrease the friction between the rotor shaft and the stator.
Types of centrifugal pumps
Centrifugal pumps are categorized into two types, depending on the impeller design.
- Radial Flow: Centrifugal pumps that use a radial flow impeller discharge the fluid at 90° to the shaft axis.
- Mixed Flow: Centrifugal pumps with a mixed flow impeller discharge fluid in a semi-axial direction or conical direction. This is a combination of radial and axial pumping action.
It is important to note that axial flow pumps are NOT centrifugal in their pumping mechanism where fluid is discharged along the shaft axis.
ANSI Pumps vs. API Pumps
Centrifugal pumps can be further classified based on their application as ANSI and API pumps.
ANSI pumps are centrifugal process pumps that adhere to the standards of the American National Standards Institute (ANSI). They can be interchanged across manufacturers and brands and are used to pump thinner fluids like water and alcohol. They are considered the pump of choice for chemical processing.
ANSI process pumps have a horizontal design with end suction and are characterized by an overhung impeller and back pull-out.
API pumps, on the other hand, are designed to meet the American Petroleum Institute (API) standard. They are capable of handling high temperatures, pressures, and emissions and are ideal for the petroleum industry. API pumps have casings, back covers, and bearing houses designed for máximum performance under oil refinery conditions.
API pumps, however, have the disadvantage of being more expensive than ANSI pumps. They are also not as versatile or as readily available in the market.
Single-stage, Two-stage, or Multi-stage
Centrifugal pumps are also classified depending on the number of impellers they have.
- Single-stage centrifugal pumps have a single impeller within the casing. They have a simple design and are easy to maintain. Its operation is perfectly adapted to situations where it is necessary to maintain a high flow rate at low pressure.
- Two-stage centrifugal pumps have two impellers inside their casing and are designed for applications where a higher head is needed. Their operation is low cost and provides a more economical option than serial pumping.
- Multi-stage: Multi-stage pumps have several impellers fitted in series on one shaft. This design allows them to act like separate pumps and develop high pressures while remaining economical in their operation.
Common Industrial Centrifugal Pump Applications
Centrifugal pumps are highly versatile, making them suitable for use across a number of industrial, agricultural, and domestic applications where movement of fluids is required. Some of these applications include:
- Distribution of water for human consumption
- Hydrant and fire protection systems
- Sewage disposal
- Bulk chemical transfer
- Food and beverage manufacturing
- Chemical manufacturing
- Mining and mineral processing
- Irrigation and drainage
- Crude oil and slurry pumping within oil & gas industries
The ideal type of pump to use will depend on how you want to treat the fluid and how the fluid enters the pump.