Problem 3.48

# Problem 3.48 - No allowance was made for the extra volume...

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Problem 3.48 [Difficulty: 5] Discussion: The design requirements are specified except that a typical floor height is about 12 ft, making the total required lift about 36 ft. A spreadsheet was used to calculate the system properties for various pressures. Results are presented on the next page, followed by a sample calculation. Total cost dropped quickly as system pressure was increased. A shallow minimum was reached in the 100-110 psig range. The lowest-cost solution was obtained at a system pressure of about 100 psig. At this pressure, the reservoir of 140 gal required a 3.30 ft diameter pressure sphere with a 0.250 in wall thickness. The welding cost was \$155 and the material cost \$433, for a total cost of \$588. Accumulator wall thickness was constrained at 0.250 in for pressures below 100 psi; it increased for higher pressures (this caused the discontinuity in slope of the curve at 100 psig). The mass of steel became constant above 110 psig.

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Unformatted text preview: No allowance was made for the extra volume needed to pressurize the accumulator. Fail-safe design is essential for an elevator to be used by the public. The control circuitry should be redundant. Failures must be easy to spot. For this reason, hydraulic actuation is good: leaks will be readily apparent. The final design must be reviewed, approved, and stamped by a professional engineer since the design involves public safety. The terminology used in the solution is defined in the following table: Symbol Definition Units p System pressure psig A p Area of lift piston in 2 V oil Volume of oil gal D s Diameter of spherical accumulator ft t Wall thickness of accumulator in A w Area of weld in 2 C w Cost of weld \$ M s Mass of steel accumulator lbm C s Cost of steel \$ C t Total Cost \$ A sample calculation and the results of the system simulation in Excel are presented below. σ π t D S 4 2 S D p Results of system simulation:...
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## This note was uploaded on 10/19/2011 for the course EGN 3353C taught by Professor Lear during the Fall '07 term at University of Florida.

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Problem 3.48 - No allowance was made for the extra volume...

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