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Pump Basics – Impellers and Volutes
Mon, October 10, 2018
Centrifugal pumps come in many configurations - in-line, base mounted, foot mounted, single and double suction, vertical and horizontal split case, close coupled and long coupled – the list goes on. No one style is best for all applications. So when should you use which? Over the course of the next few blogs, we are going to look at each and give you a better understanding of why a manufacturer would go through the trouble of designing and manufacturing a given style of pump. Today, we'll start with pump basics. In short, a centrifugal pump consists of five basic components, a volute (also known as a diffuser), an impeller, a motive force such as an electric motor, a coupler (which may be the motor shaft itself), and brackets/bases to hold everything together. Impellers come in all shapes and sizes. Closed or shrouded impellers have vanes that are covered on both sides. Open impellers have just enough shrouding to provide support for the vanes as they rotate and move the fluid. [caption id="attachment_2430" align="aligncenter" width="397"]
Example of a closed (shrouded) impeller[/caption]
For our purposes, we will look at closed impellers. These are meant for clean water applications.
The impeller imparts velocity to the water. Water enters the eye of the impeller where it encounters a centrifugal force caused by the rotation of the impeller itself. From here, it accelerates along the impeller vanes, leaving the impeller at a velocity as near to the impeller tip speed as possible.
Notice we didn’t say that the impeller changes the pressure - that happens in the volute. The volute provides three functions:
Water flow through a typical impeller/volute[/caption]
It’s the volute that creates the change in pressure based on the volume and velocity of the water coming off the tips of the impeller vanes.
Next – Pump curves and what it all means.
Tags: bell & gossett , Bornquist , centrifugal pumps , Education , Educator , HVAC , impeller , volute
Centrifugal pumps come in many configurations - in-line, base mounted, foot mounted, single and double suction, vertical and horizontal split case, close coupled and long coupled – the list goes on. No one style is best for all applications. So when should you use which? Over the course of the next few blogs, we are going to look at each and give you a better understanding of why a manufacturer would go through the trouble of designing and manufacturing a given style of pump. Today, we'll start with pump basics. In short, a centrifugal pump consists of five basic components, a volute (also known as a diffuser), an impeller, a motive force such as an electric motor, a coupler (which may be the motor shaft itself), and brackets/bases to hold everything together. Impellers come in all shapes and sizes. Closed or shrouded impellers have vanes that are covered on both sides. Open impellers have just enough shrouding to provide support for the vanes as they rotate and move the fluid. [caption id="attachment_2430" align="aligncenter" width="397"]
Example of a closed (shrouded) impeller[/caption]
For our purposes, we will look at closed impellers. These are meant for clean water applications.
The impeller imparts velocity to the water. Water enters the eye of the impeller where it encounters a centrifugal force caused by the rotation of the impeller itself. From here, it accelerates along the impeller vanes, leaving the impeller at a velocity as near to the impeller tip speed as possible.
Notice we didn’t say that the impeller changes the pressure - that happens in the volute. The volute provides three functions:
- To keep the water from spraying all around the room
- To provide a relatively smooth channel for the water to travel on its way to the discharge opening
- To reduce the velocity of the water, thus increasing pressure (we will talk about the velocity/pressure relationship later)
Water flow through a typical impeller/volute[/caption]
It’s the volute that creates the change in pressure based on the volume and velocity of the water coming off the tips of the impeller vanes.
Next – Pump curves and what it all means.
Tags: bell & gossett , Bornquist , centrifugal pumps , Education , Educator , HVAC , impeller , volute
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