Click here for Pump Challenge #1: An Impeller Cut Problem

Statement of a problem: A pump had been operating for many years at the bottom of a dry pit, connected to an open wet pit, which contains hot water at 150 deg F. A mechanical seal would periodically fail, with typical time between repairs ranging from only 2 to 3 months. To eliminate the need to climb down the dry pit to do frequent repairs, it was decided to relocate the pump to the top of the grade. The pump design was self-priming, so priming was not considered an issue.

After work was completed, the operators started having problems with the pump not being able to deliver flow. The problem seemed sporadic; sometimes the pump operated fine, but sometimes it did not. Operators also noticed that the pump was occasionally noisy.

Given: Pump performance and NPSH curve. Vapor Pressure chart.

Question 1: What is the problem?

Question 2: What caused the seal failures before the pump was relocated?

Pump Challenge #2

Can you crack this one? Go for it! Please send answers to Dr. Nelik.

Click here for the solution.

Click here for the Pump Challenge #3.

Tags: August 2009 Issue , Centrifugal Pumps , Pumping Prescriptions , Pumps

Comments (2)

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Interesting
written by anonymous, July 24, 2009

this is an interesting article, thank you!

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written by Ian Simpson, August 27, 2009

Without getting too academic and delving into the in's and out's of "sporadic; sometimes the pump operated fine, but sometimes it did not. Operators also noticed that the pump was occasionally noisy."
I would appear that the pump is cavitating at low sump levels (question 1) resulting from insufficient NSPHa and this was also the problem with the premature seal failure (question 2) when operating at low sump levels.

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