Rebuilding a Practically
Destroyed Impeller
Alfredo A. Ciotola, Frontline Industries, Inc.
We were told that the 48-in diameter sewage pump
impeller from one of New York City’s main sewage
pumps had been found “practically destroyed.”
When the impeller actually arrived at our location, both the
shop foreman and the service manager asked, “Where is the
other half?”
After realizing that there was no other half, they both
looked puzzled and somewhat worried. Some of their concerns were voiced at our internal planning meeting, where we
tried to set a proper course for the repair:
• How are we going to build the suction half of the impeller from only an old “one line drawing” that really has no
details of the vanes, especially the section that attaches to
the suction ring?
• How are we going to make sure that we do not considerably change the flow characteristics of the original impeller
and risk doing a lot of work for nothing?
• How are we going to “attach” the old half of the impeller
to the new one, in a way that creates a sound and integral
bond that will not fatigue and fail at a later date?
• How are we going to measure/calculate the weight distribution during the positioning of the four new vanes in a
way that it will not create a dynamic balancing nightmare
later on?
Any of these potential problems would have been
enough to discourage most repair facilities from undertaking such a challenging repair job. However, at the end of our
strategy meeting the consensus was unanimous: we would
apply our combined knowledge, field experience and basic
common sense to develop and implement the best possible
solution under these circumstances.
Here is the piece left over of the original We had a foundry cast a ring and set it at Following the existing profile, we built a
48-in diameter impeller. the right height, following a customer’s vane made out of reinforced plaster, then
dimensional drawing. cut out the vane and sent it to a foundry to
be reproduced.
The foundry provided four identical vanes. We then trimmed off the existing impeller The four new vanes were carefully set in
Here are two of them. vanes uniformly. place and welded to the ring and to the hub.
