What is a Centrifugal Pump?
A centrifugal pump is a mechanical device designed to move fluid by means of the transfer of rotational energy from one or more driven rotors, called impellers. Fluid enters the rapidly rotating impeller along its axis and is cast out by centrifugal force along its circumference through the impeller’s vane tips.
The action of the impeller increases the fluid’s velocity and pressure and also directs it towards the pump outlet. The pump casing is specially designed to constrict the fluid from the pump inlet, direct it into the impeller and then slow and control the fluid before discharge.
Centrifugal pumps are used to transport fluids by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow. The rotational energy typically comes from an engine or electric motor. They are a sub-class of dynamic axisymmetric work-absorbing turbomachinery.
The fluid enters the pump impeller along or near the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or volute chamber (casing), from which it exists.
Common uses include water, sewage, agriculture, petroleum, and petrochemical pumping. Centrifugal pumps are often chosen for their high flow rate capabilities, abrasive solution compatibility, mixing potential, as well as their relatively simple engineering.
A centrifugal fan is commonly used to implement an air handling unit or vacuum cleaner. The reverse function of the centrifugal pump is a water turbine converting the potential energy of water pressure into mechanical rotational energy.
Parts of Centrifugal pumps
- Impeller: Impeller is a rotor used to increase the kinetic energy of the flow.
- Casing (Volute): The casing contains the liquid and acts as a pressure containment vessel that directs the flow of liquid in and out of the centrifugal pump.
- Shaft (Rotor): The impeller is mounted on a shaft. A shaft is a mechanical component for transmitting torque from the motor to the impeller.
- Shaft sealing: Centrifugal pumps are provided with packing rings or mechanical seal which helps prevent the leakage of the pumped liquid.
- Bearings: Bearings constrain the relative motion of the shaft (rotor) and reduce friction between the rotating shaft and the stator.
How does a centrifugal pump work?
The impeller is the key component of a centrifugal pump. It consists of a series of curved vanes. These are normally sandwiched between two discs (an enclosed impeller). For fluids with entrained solids, an open or semi-open impeller (backed by a single disc) is preferred.
Fluid enters the impeller at its axis (the ‘eye’) and exits along the circumference between the vanes. The impeller, on the opposite side to the eye, is connected through a drive shaft to a motor and rotated at high speed (typically 500-5000rpm). The rotational motion of the impeller accelerates the fluid out through the impeller vanes into the pump casing.
There are two basic designs of pump casing: volute and diffuser. The purpose in both designs is to translate the fluid flow into a controlled discharge at pressure.
In a volute casing, the impeller is offset, effectively creating a curved funnel with an increasing cross-sectional area towards the pump outlet. This design causes the fluid pressure to increase towards the outlet.
The same basic principle applies to diffuser designs. In this case, the fluid pressure increases as fluid is expelled between a set of stationary vanes surrounding the impeller. Diffuser designs can be tailored for specific applications and can therefore be more efficient.
Volute cases are better suited to applications involving entrained solids or high viscosity fluids when it is advantageous to avoid the added constrictions of diffuser vanes. The asymmetry of the volute design can result in greater wear on the impeller and driveshaft.
Centrifugal Pump Applications
Centrifugal pump uses are common throughout a diverse range of domestic, commercial, and industrial markets.
Examples of centrifugal pump applications include but are not limited to:
- Water supply for residential areas
- Fire protection systems
- Sewage/slurry disposal
- Food and beverage manufacturing
- Chemical manufacturing
- Oil and gas industrial operations
Advantages of centrifugal pump
- As there is no drive seal so there is no leakage in pump
- It can pump hazardous liquids
- There are very less frictional losses
- There in almost no noise
- Pump has almost had 100% efficiencies
- Centrifugal pump has minimum wear with respect to others
- There is a gap between pump chamber and motor, so there is no heat transfer between them
- Because of the gap between pump chamber and motor, water cannot enter into motor
- Centrifugal pump uses magnetic coupling which breakup on high load eliminating the risk of damaging the motor
Disadvantages of centrifugal pump
- Because of the magnetic resistance there is some energy losses
- Unexpected heavy load may cause the coupling to slip
- ferrous particles in liquid are problematic when you are using magnetic drive. This is because particle collect at impeller and cause the stoppage of pump after some time