The main rotating pumping element in a Centrifugal Pump, The impeller comes in many different shapes and sizes determining different applications and considerations on selection and Applications.
The impeller transfers the torque or rotational movement from the motor, steam turbine, or basically any driver coupled to the pump onto the medium being pumped. The Geometry of the pump impeller comprehends some veins irradiating from the eye or hub and most of the time accompanied by frontal and/or rear shrouds that push the medium being pump against the Pump Casing.
The operation of the pump impeller as it rotates works by the vanes exerting or directing the medium from the hub towards the end of the vanes inducing a centrifugal force and increasing the pressure exerted to increase the final differential pressure. It is noticeable that different shapes and sizes will determine the way the medium being pumped is handled by impeller.
Common Pump Impeller Types
There are five major impeller designs in Centrifugal Pump construction nowadays. These different type of impellers are used according to their advantages in many different types of Centrifugal Pump applications.
Open Impeller Types
An open impeller has vanes that are attached to the eye or hub which at the same time is coupled to the pump shaft. There is no shroud or wall surrounding the vanes front or back making open impellers more susceptible to vane failure than a closed or semi-closed impeller.
Some of advantages of open impellers are the handling of suspended solids in the media with relatively ease compared to some of its counter parts. Furthermore, Open impellers are relatively easier to clean and repair due to not having front or back shrouds.
Semi-Open Impeller Types
Semi-Closed impeller’s anatomy adds a shroud or plate to the back of the impeller and acts as the vanes are webbed increasing the strength mechanically of the vanes. It is a middle ground between an open impeller and a closed impeller. Semi Open impellers are of medium efficiency are used on most average size centrifugal pumps. They are not as good as open impellers in handling applications with solids but still an improvement over or next type of impellers, the close impeller. There are further design conflicts on certain applications where the gap between the semi open impeller and the casing of the pump is large enough that some fluid goes back into the start of the vanes recirculation and slipping. This issue makes the Semi open impeller less effective in some applications.
Closed impeller Type
After seeing the construction anatomy of an Open and Semi Open Impeller, we can now step into the most logical step in impeller construction and the is the Close Impeller. As the sequence inherits, the close impeller comprehends of the same hub and eye with vanes protruding out to the outer part of the circumference. However, this time the impeller will have a shroud in the back and front of the vanes making it a more robust and mechanically sound strong impeller. This structure will provide its advantages and disadvantages as a close impeller will have a very low NPSH requirement and provide a very efficient flow in comparison to its predecessors. however, that close design make this impeller very inefficient when handling suspended solids as they are extremely prone to clog. the intrinsic design of close impellers almost certain requires the use of wear rings to increase efficiency.
Vortex impeller Type
Although very similar in shape to a semi open impeller, vortex impellers differ in shape and certain advantages in pump applications. Previous mentioned impellers developed a channel between the vanes and the shroud; however, vortex impellers have more space between the impeller itself and the casing creating a vortex in the fluid where solids avoid contact with the impeller itself. It is primarily used in solid applications such as waste water and alike due to this property from its configuration. However, the vortex impeller efficiency is diminished when in comparison to a semi open or close impeller.
Screw Impeller Type
One step up from the vortex impeller in solid handling capability is the Screw Impeller Type. Its design aligns more with a progressive channel that allows for solids to be openly handle when rotating. It has a low shear ratio, making it suitable for special applications that are delicate to pump. Its high efficiency, anti clogging properties , and low shear makes it ideal for specific applications. Due to its anatomy, Screw Impellers are used in end suction pumps.
Chopper or Cutter Impeller Type
Chopper or Cutter impellers are modified impellers to work in certain applications where the used of a solid reducing mechanism is require for its optimal performance. Solids are reduced in size, shredded, as they are being pumped to prevent clogging and ultimate failure of the unit. its ability to reduce solids as it wears and pumping efficiency are diminished as the impeller accumulate hours of operation.
Impeller Selection and Sizing
Selecting the right impeller type for your application is crucial for the most effective performance and correct functioning of your pump. ACCA Pumps manufactures impellers in many different types and alloys ensuring that you will receive the most well reversed engineer impeller with todays manufacturing techniques of 3d printing and castings. We can provide you from any sample a new impeller that not only will fit your pump but perform as the Original Equipment Manufacturer or better. If you would like to inquire about our capabilities of selecting and manufacturing current applications, please contact us.