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Semi-open or closed impeller?

Semi-open or closed impeller?

Release time:
2019/05/11 16:00
Semi-open or closed impeller? 
The design of the slurry pump impeller is not related to a closed or open confguration. This is determined by production aspects and what type of applications the impeller will be used on.
Closed impellers
Closed impellers are by nature more efcient than open impellers, due to the reduction of “short circuiting” leakage over the vanes. The efciency is less affected by wear, “If you are looking for efciency - use a closed impeller whenever possible!”
Semi-open impellers
Semi-open impellers are used to overcome the limitations of a closed design and depend on impeller diameter, size or structure of the solids, presence of entrained air, high viscosity, etc. 
The efciency is slightly lower than for closed impellers. 
Impeller diameter
“The diameter of an impeller governs the amount of head produced at any speed.” The larger the diameter of the impeller the greater the head produced. A large diameter impeller running very slow would produce the same head as a smaller impeller running much faster (key aspect when it comes to wear, see section Wear Protection.
To make it simple:
For highly abrasive duties we use large impellers giving long life and reasonable efciencies.
So even if larger impellers are more expensive and have slightly lower efciency, they give a better pay off in highly abrasive duties.
For abrasive duties where wear is not the primary concern, smaller impellers are more
economical, and offer better efciency.
This relation is known as:
Impeller Aspect Ratio (IAR) = Impeller diameter / Inlet diameter
for highly abrasive duties we use IAR = 2.5:1
for abrasive duties we use IAR = 2.0:1
for mildly abrasive duties we can use IAR of less than 2.0:1
All the above parameters have been considered when designing the Tobee slurry pump ranges, giving optimal operation economy at various duties.
Impeller width
"The width of the impeller governs the flow of the pump at any speed.” A large width impeller running slowly could produce the same flow rate as a thinner impeller running faster, but most important - the velocity relative to vane and shroud would be considerably higher.
Compared to water pumps and depending on the “wear profle”, slurry pumps normally have impellers that are not only larger, but very much wider.