Finding if the correct pump is installed

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Discussion Overview

The discussion revolves around assessing whether a pump is appropriately sized for its application, particularly in the context of cavitation issues. Participants explore methods to calculate flow rates and factors influencing pump performance, including system layout and net positive suction head (NPSH).

Discussion Character

  • Technical explanation
  • Exploratory
  • Debate/contested

Main Points Raised

  • One participant suggests calculating the flow rate in lbs/hr using the formula: 60 GPM * 60 minutes * 8.33 lbs/gal, assuming no cavitation occurs.
  • Another participant proposes measuring the actual outflow rate by collecting water in a container for one minute if cavitation is present, as this would provide a more accurate assessment.
  • There is a suggestion to restrict outflow to determine the flow rate at which cavitation ceases, noting that this would involve estimating the relationship between restriction diameter and output diameter.
  • One participant raises the importance of considering the NPSH in the system, indicating that excessive suction on the inlet may be contributing to cavitation.
  • A request for more details about the specific system layout is made to better understand the context of the problem.

Areas of Agreement / Disagreement

Participants express varying approaches to addressing the cavitation issue and calculating flow rates, indicating that multiple competing views remain without a consensus on the best method or solution.

Contextual Notes

Limitations include potential missing assumptions about the system's design and operational conditions, as well as the need for specific measurements that may not be feasible in all situations.

precog
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I am having problems with a pump installed.

I am trying to determine if it is to large for the application because there is a lot of cavitation during the process. I have the pump information 60GPM with a 5Hp Motor. RPM is 1725. How can i calculate lbs/hr of the fluid flowing?
 
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For water @8.33lbs/gal:
Code:
60(gallons per minute)  * 60(minute in an hour) * 8.33
if the pump never cavitates... this would be the max possible flow.
If the pump cavitates, you'll have to measure the actual outflow rate for one minute which is arguably the best solution. Get a forty gallon container, direct the output into the container for one minute. Substitute that value into the equation above.

If that is physically impossible you will have to estimate your flow. Can you restrict outflow? If so keep restricting outflow until no cavitation occurs. Then estimate what the reduced flow is as a function of the restriction diameter vs the output diameter.
There will be slop in there, because as head pressure goes up, the pump has to not only lift water, but also push it out through the restriction. Remember Bernoulli.

Sorry if this is excessivley trivial, but I can't tell what your situation is.
 
If the pump is cavitating, I would look at the NPSH you have in your system. It sounds like you are trying to pull to much on the inlet.
 
Can you tell us a little more about your specific system layout?
 

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