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Impellers: solid hub versus hollow core



Q  -  Years ago, impellers with hollow core (cored impellers) were widely used.
Because of their cored patterns these impellers are lighter, cheaper, and easier to
install, or remove.

These days, many industry standards require the use of impellers with solid hub.
Hollow cored impellers are either prohibited, or require the approval of the users.
What is the reason for this change?


A  -  Impellers are normally mounted on the shaft with shrink fit (tight fit) that
requires the impellers to be heated to expand prior to their installation to, or
removal from, the shaft.

A hollow core (or hollow hub) impeller that has been used for sometime can have
the liquid, or gas from the liquid, entrapped in its hollowed core. Heating the hub
to remove the impeller can cause the liquid to vaporize, or for pressurized gas to
escape at elevated temperature, and its uncontrolled release can cause harm or
injury to a person, more so if the liquid is flammable, volatile, hazardous, or toxic.

To minimize the risk, a cored impeller can be drilled with a pair of tiny holes to vent
its core. But this safety measure is not advisable for impeller handling flammable,
volatile, hazardous, or toxic liquid because the rotor, when removed for routine
inspection or maintenance, cannot be decontaminated without disassembling the
impeller from its shaft.


R: 1109-IMSO
C: design
F: impeller cored


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