Centrifugal pumps are similar to barrel pumps, mechanical devices that have been designed for transporting fluids by transporting rotation energy from one or multiple impellers, which are driven rotors. Fluid enters into the fast-rotating impeller along the axis. Centrifugal force then casts it out along the circumference through the vane tips of the impeller. The impeller’s action increases the pressure and velocity of the fluid and sends it in the direction of the pump outlet. The casing of the pump is specifically designed for constricting the fluid from the inlet of the pump, directing it towards the impeller and then slowing and controlling the fluid before it is discharged.
How Do Centrifugal Pumps Work?
The key component in centrifugal pumps is the impellers. It is made up of curved vanes. Normally they are sandwiched in between two discs (or an enclosed impeller). It is preferable to have a semi-open or open impeller for fluids that have entrained solids.
There are two main pump casing designs: diffuser and volute. In both designs, the purpose is translating the flow of the fluids into a discharge that is controlled at pressure.
Design of Centrifugal Volute Casing
Diffuser designs have the same basic principle applied to them. In this particular case, there is an increase in pressure as the fluid gets expelled between stationary vanes that surround the impeller. It is possible to tailor diffuser designs for specific applications which can make them more efficient. A volute case is best suited for applications that involve high viscosity fluids or entrained solids when avoiding the diffuser vanes’ added constrictions is advantageous. The volute design is asymmetrical which can result in the impeller’s drive shaft experiencing greater wear.
Design of Centrifugal Diffuser Case
What are the main features of centrifugal pumps?
There are two major families of pumps: positive displacement and centrifugal pumps. When compared to positive displacement pumps, usually centrifugal pumps are specified to pump lower viscosity liquid, as low as 0.1 cP and for higher flows. In certain chemical plants, centrifugal pumps will make up 90% of all pumps that are in use. However, it is preferable to use positive displacement pumps in a number of different applications.
What Limitations Do Centrifugal Pumps Have?
In order for a centrifugal pump to operate efficiently, it relies on the impeller having a high-speed, constant rotation. Centrifugal pumps will become increasingly inefficient when there are high viscosity feeds. Higher pressure and greater resistance are needed in order for a certain flow rate to be maintained. Generally speaking, centrifugal pumps are best suited for high capacity, low-pressure pumping applications with liquids that have viscosities ranging from 0.1 to 200 cP.
High viscosity oils or slurries like mud may cause overheating and excessive wear which can result in premature failures and damage. Positive displacement pumps frequently run at much lower speeds. This makes them much less prone to having these types of problems.
Any kind of pump medium sensitive to shearing (the process of separating biological liquids, slurries, or emulsions) can become damaged as a result of the high speed of the impeller on a centrifugal pump. In these cases, it is preferred to have a positive displacement pump’s lower speed.