When it comes to the transfer of liquids, Centrifugal Pumps are the most popular choice. These everyday workhorses can be found across many industries, providing mission-critical solutions wherever the movement of liquid is essential. Let's take a look at why centrifugal pumps are so popular.
Related Blog: Understanding How to Measure a Pump's Performance
History
One of the first centrifugal pumps in use was put into service in 1475. Francesco di Giorgio Martini was credited with the device, and it was called a mud lifting machine. However, real centrifugal pumps were not developed until the late 17th century. At that time, Denis Papin designed and created a straight vane version.
The curved vane pump as it is in operation today was created by British inventor John Appold in 1851.
How They Work
As the name implies, centrifugal pumps use centrifugal force to pump liquids from one location to the other. They are designed to transform provided rotational energy into work to raise a liquid from a low level to a high level.
A centrifugal pump uses only two main parts for its conversion of energy - the impeller and the casing. The impeller is the part of the pump that rotates, and the casing forms an airtight passage around the impeller.
When fluid enters the casing, it hits the impeller blades. From there it is whirled tangentially and radially outward to the diffuser part of the casing. The fluid picks up both pressure and velocity as it acted upon by the impellers. The doughnut-shaped diffuser decelerates the flow and further increases the pressure. The process then repeats as the impeller turns.
Factors Affecting Performance
There are several factors that can affect the performance of a centrifugal pump. These factors need to be considered when choosing a pump for a given purpose. These factors are:
Fluid Viscosity - The viscosity of the liquid to be pumped can affect pump performance. Viscosity can be defined as the liquid's resistance to shear. Since a centrifugal pump generates high liquid shear through its pumping process with the impellers, most centrifugal pumps are better suited for low viscosity fluids.
Operating Temperature and Pressure - A pump designed for high-temperature operation is going to need special seals capable of withstanding the material. When it comes to a high-pressure condition, the pump casing may need to be reinforced to stand up to the pressures created.
Liquid Vapor Pressure - Fluids will turn into a vapor at a given pressure. If this pressure is achieved during the pumping operation, it can cause bearing damage. For this reason, the vapor pressure of the liquid must be known and pump pressure calculated to prevent cavitation from evaporation.
Fluid Specific Density and Gravity - The weight of a liquid will directly affect a centrifugal pump and how much work it can do with the selected material. The density of a fluid is defined as its mass per unit of volume. The gravity is a ratio between this density and the density of water. As you might expect, liquids with a gravity higher than water are going to take more power to pump.
Net Positive Suction Head (NPSH) - NPSH refers to the pressure on the suction side of the pump. As in liquid vapor pressure, cavitation needs to be avoided during the pumping process. To make sure that this doesn't happen during operation, the Net Positive Suction Head Available (NPSHA) must be greater than the Net Positive Suction Head Required (NPSHR.)
Centrifugal Pump Types
Centrifugal pumps are often classified based on the number of impellers they contain. A single stage pump contains a single impeller and is the easiest to maintain. Single stage pumps are used in high flow rate applications where there is low pressure. You will find these in low Total Dynamic Head (TDH) applications.
(It should be noted that TDH is roughly defined as the total equivalent height that a liquid is going to be pumped. The TDH calculation takes into account the frictional losses in the pipe itself. TDH is equal to the static height plus the static lift plus the friction loss.)
Two-stage pumps employ double impellers that operate side by side. These are used in medium TDH applications.
If a high-TDH service application is required, a multi-stage centrifugal pump can be used. A multi-stage centrifugal pump uses three or more impellers in a series to get the lift capability required.
Applications
Centrifugal pumps can be found in any number of applications where liquids need to be transported. You will find them in many of the nation's water and wastewater plants, where they pump the water for the municipal services.
They can also be found in many industrial plants, including petroleum, chemical, pharmaceutical, and other applications. Most vacuum cleaners are a modified version of a centrifugal pump, designed to move air instead of liquids.
Mader Electric, Inc. specializes in centrifugal pump repair and installation, as well as pump training. Contact us to see how we can help with your pumping needs.
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