Centrifugal Pumps – What You Need To Know



 

Centrifugal pumps are mechanical devices that have been designed to move fluid by transferring rotational energy into fluid pressure. This is achieved through one or several driven rotors known as impellers. The primary function of the impeller is to increase fluid velocity and pressure, which is then directed towards the pump’s outlet. Generally, the pump’s cast has been designed to constrict the fluid from its inlet.

How Centrifugal Pumps Work

Every component in a pump plays a huge role in either directing or increasing velocity and pressure. However, the impellers are vital components in which without, the pump will not work. In other words, impellers are the most important in a centrifugal pump. Impellers come in different designs and have a series of curved vanes, which are sandwiched between two discs (for enclosed impellers). When it comes to fluids with solid matter, then an open or semi-opened impeller is best. Taking a look at flux pumps will help in understanding more of the options given.

When it comes to pump casting, there are two basic designs which are: Volute and Diffuser. The primary purpose of each design translates to the fluid’s flow (controlled pressure discharge).

Volute Casting Design Vs. Diffuser Case Design

The truth is that both apply similar basic principles to diffuser design. Diffuser designs can be tailored to a specific application, which is why they are the most efficient. On the other hand, volute casting design best suits applications that involve solid matter or fluids with high viscosity. However, the unevenness of the volute design will often lead to greater wear of the driveshaft and impeller.

The Main Features of a Centrifugal Pump

Pumps can be categorised under two main families which are: centrifugal and positive displacement pumps. Unlike positive displacement pumps, centrifugal pumps are generally designed for high flows and low viscosity liquids (below 0.1cP). About 90% of pumps found in chemical plants are centrifugal pumps. However, there are specific applications which will demand positive displacement pumps.

The Limitations of Centrifugal Pumps

For centrifugal pumps to be efficient, they rely on the constant high-speed rotating impellers. However, when it comes to fluids with high viscosity, centrifugal pumps are less effective. That is because they experience high resistance, and high pressure is required to maintain a specific flow rate. Therefore, a centrifugal pump will struggle to maintain pressure when it comes to thick fluids of up to 200cP. In fact, it will make a motor overheat. Also to be considered is Fleet BioPocessing, this engages you further.

In other words, thick fluids such as mud, high viscosity oil, and others will cause excessive wear and overheating. All these are a recipe for damage and premature pump failures. Therefore, when it comes to high viscosity fluids, it is wise to invest in positive displacement pumps. These pumps operate at low speeds and less prone to problems found in centrifugal pumps.

Another limitation is that the high speed of the impeller may damage any fluid that is sensitive to shearing (such as biological or slurries liquids) in a centrifugal pump. In such a case, it is wise to consider low-speed positive displacement pumps.

 

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