| General > General Technical Chat |
| Why is the curvature of pump rotor blades "backwards"? |
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| Ground_Loop:
The comparison with a fan is not very good as a fan is axial flow whereas a centrifugal pump is radial flow. Also, if you look at the impeller at flow entry whether fan or cent pump the fluid 'sees' forward swept vanes. At the exit the fluid 'sees' reverse swept vanes. I have seen only one example where the reverse was true. I had a dishwasher whose pump had extreme swept impeller blades that upon reversing would actually pump water from the pump casing back through the impeller eye to drain the basin. Forward rotation was trailing blades at impeller exit and pumped water through the wash bars. Generally, straight blade are for high flow and swept blades are for high pressure. |
| CatalinaWOW:
There may be additional factors besides the 'pump theory' ones mentioned before. If the pump is designed with little or no clearance to the blade tips, friction between the blade tip and wall will tend to drag a forward facing blade into the wall, with the reverse for a backward blade. In one case increasing pump power requirements and reducing leakage, while the other case minimizes power at the potential cost of leakage. Chatter could result from the forward configuration. Several other possibilities. |
| beanflying:
Some of what has been posted above isn't really correct. Centrifugal Pumps come in a range of types from Axial, Radial and Mixed Flow impellers depending on application Also they can be run in reverse (tips forward for a crude description) but they run very inefficiently with lower flow and reduced pressure (Typically in the 25-30% range). |
| Ground_Loop:
Centrifugal pumps are by definition radial flow. Fluid may flow through the casing axially, but within the impeller it is only radial. |
| beanflying:
Tell that to the industry :o Axial Flow impellers do not have the fluid flow radially in the casing at all (middle of the picture above). Typical applications are high flow low head applications like flood irrigation or ground dewatering and in some cases longer shaft drives are used. The impeller is a propeller and just because it spins radially doesn't mean the flow past the impeller is. Some more reading here https://www.batescrew.com/axial |
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