03 Aug What you should know about Centrifugal Pumps
In many industries and at home, it is often necessary to transfer water over long distances via a pipeline. To achieve this transfer, one must employ a device that can convert mechanical energy into hydraulic energy. Among the options commonly used to generate the necessary mechanical energy are centrifugal pumps. To understand how these units work, one should first look at their five main components. These are the shaft, impeller, casing, and suction and delivery pipes.
Structure and Operating Principle
The impeller is a fan-like structure consisting of several curved vanes and is mounted on a rotating shaft driven by a motor located outside of the casing. The airtight casing, which protects the moving parts and contains the water, has a suction pipe through which the water enters and a deliver pipe through which it is later discharged. Centrifugal pumps rely on the rotational forces generated by the impeller vanes to draw in water through the suction pipe and transport it at increased pressure to the delivery pipe. A one-way valve located in the entry port ensures the water can only travel forwards, while an external strainer prevents the entry of any solid bodies that might otherwise damage the pump’s moving parts or cause a blockage.
However, the casing is more than a mere watertight container. In practice, its geometry can play a significant role in determining the performance characteristics of centrifugal pumps. There are three types; volute, vortex, and fitted with guide blades. In the volute type, the impeller is located eccentrically, resulting in a casing with a spiral cross-section whose area gradually increases as it nears the exit port. The spiral shape reduces the flow rate, which causes an inverse pressure increase.
In the vortex casing, the impeller is mounted centrally to provide a circular cross-section that is markedly less prone to eddy formation. When positioning guide blades around the impeller, these act as diffusers, slowing the flow rate and further boosting the outlet pressure in this variant of the centrifugal pump. In each case, varying the speed of the motor offers the operator a means to adjust the unit’s flow rate and outlet pressure. There is a performance curve for each device, which indicates the relationship between its speed of rotation, flow rate, and pressure.
In addition to the type of casing, a second design feature also affects the performance of this type of pumping device, namely the number of impellers it has. Models with just a single impeller are best suited for use in applications that involve transporting high volumes of a liquid at relatively low pressures. However, correspondingly more powerful centrifugal pumps are possible when introducing one or more additional impellers. The resulting units can cope with more viscous fluids and handle applications that require generating higher outlet pressures.
The Pros and Cons
Because of their simple design and the limited number of parts, centrifugal pumps are less prone to wear and tear and tend to produce less noise than other pump types. That structural simplicity also means they are less expensive than alternative pump types. Due to the gap between the fluid compartment and the external motor, there is no risk that its contents could become overheated. The distance between the two also means that pumped fluids cannot easily penetrate the motors of centrifugal pumps.
In some models, the coupling between the motor and the impeller is not mechanical but magnetic. The design eliminates the need for a potentially vulnerable drive seal that might subsequently become worn and begin to leak. Furthermore, manufacturing their parts from suitably resistant materials can enable these modified units to handle hazardous liquids without sustaining any significant damage.
Any excess strain that might arise due to an unusually high load acts to break the magnetic connection, thus preventing the motor from sustaining any damage while also pausing these mag drive centrifugal pumps in the process.
However, no technology is entirely without its shortfalls, although, in this case, these are comparatively few. Ultimately they are unable to equal the high pressures or precision obtainable by reciprocating models. However, these models are designed to produce a continuous stream of liquid rather than the fixed-measures produced by the reciprocating action of a plunger or piston.
If you are in the market for world-class centrifugal pumps and accessories, be sure to contact South Africa’s industry leaders at Prochem Chemical Pump Manufacturers.