Impeller Types in Centrifugal Pumps
The impeller's basic function is to transfer the mechanical energy coming from the motor via the shaft to the fluid passing through it, imparting a certain pressure and flow to the liquid or gas.
Given the diversity of raw materials used in production, it is essential to transfer liquids with very different characteristics from one another. As these liquids and their properties change, the type of impeller used in the pump must also change accordingly. For example, the impellers of a slurry pump used in mining, an irrigation pump and a wastewater pump need to be different from one another. Each impeller type carries certain advantages and disadvantages depending on its intended use.
Open Impeller
As shown in the figure, an open impeller is a type formed by vanes extending at an angle from a central hub, with no restriction on the front side and a partial shroud on the back side. It is generally used to transfer wastewater containing solid particles, or, when manufactured from stainless material, fluids containing food products.
Because its solids-handling capability is high, it is quite ideal for processes with a risk of clogging. However, because the fluid is not compressed by the impeller, pump efficiency is unfortunately low.
Closed Impeller
A closed impeller, is closed on both the front and back surfaces in order to fully pressurize the fluid. In this way, the fluid entering the impeller is compressed between the front and back shrouds, and, along with the rotational motion of the impeller, energy flows directly from the vanes into the fluid. It is used in many applications and is the main impeller type used unless there is a special requirement. Although it can be used with different types of fluid by enlarging the impeller or changing the vane opening, there is a risk of clogging when the fluid contains particles, and it is quite difficult to clean.
Semi-Open Impeller
This impeller type is actually the version of the open impeller discussed above, with the back side fully closed. That is, the back surface of the impeller prevents fluid from escaping, while there is no restriction on the front side. A semi-open impeller is preferred for fluids that may occasionally contain solid particles, but where these particles are smaller in size and less frequent. Although it is more efficient than an open impeller, it cannot reach the efficiency levels of a closed impeller.
These three impeller groups that we have discussed form the basic structure and logic; beyond these, there is a very wide variety of impeller types that manufacturers develop according to the processes they specialize in, some examples of which are given below. What matters here is determining the impeller type best suited to the process in question.
Source: KSB Global
