TFS · Practice Exam 1 · Problem 50PDFSolution in PDF ↓
TFS · Practice Exam 1 · Problem 50
Problem & Solution
Video Synthesis
- Problem: The flow rate at the operating point of a 7.5 horsepower pump described by the pump curve below is 300 GPM.
- Key values: 74 %, 78 %, 75 %
- Result: And that equals about 78.7 feet, which is closest to answer choice D.
- ✅ Answer: D
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Student questions asked in live office hours about this problem
OH 44
Q: On the TFS practice exam problem, shouldn't the operating point be where the 7.5 hp dashed line intersects 300 gpm (giving 72 feet of head), rather than where the 8 inch impeller curve intersects 300 gpm?
A: It's a trap—you must select the largest pump that consumes up to but not exceeding the available horsepower. At 7.5 hp, that's the 8 inch impeller; choosing a larger impeller would demand more power than available and be operationally flawed. So you follow the 8 inch curve to get ~60 feet, then apply efficiency.