How to calculate fountain GPM for a fountain height of 120 feet

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Discussion Overview

The discussion revolves around calculating the gallons per minute (GPM) required for a fountain to shoot water 120 feet high, given a nozzle diameter of 2 inches. Participants explore the necessary equations and concepts related to fluid dynamics, specifically focusing on the relationship between kinetic and potential energy, as well as the calculation of liquid horsepower for the pump.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant requests assistance in finding the GPM and minimum liquid horsepower needed for a fountain, indicating a lack of familiarity with the relevant equations.
  • Another participant suggests using conservation of energy to determine the exit velocity of the water from the nozzle.
  • There is a discussion about the relationship between flow rate (Q), velocity (V), and cross-sectional area (A), with some participants expressing uncertainty about how to derive Q without knowing the velocity.
  • Equations for kinetic energy (KE = 1/2 mv²) and potential energy (PE = mgh) are provided, with a suggestion to equate them to find the velocity.
  • One participant calculates a velocity of 88 ft/s and attempts to derive the flow rate in GPM, later reporting a result of 861 GPM.
  • There is a query about how to calculate liquid horsepower, with a participant noting the formula for liquid horsepower (LHP = (Q x HP) / 3960) but expressing uncertainty about the value for HP.

Areas of Agreement / Disagreement

The discussion reflects a lack of consensus on the specific equations and values needed to complete the calculations, with participants expressing uncertainty and seeking clarification on various aspects of the problem.

Contextual Notes

Participants have not reached a definitive conclusion regarding the calculations, and there are unresolved questions about the appropriate values to use for horsepower in the liquid horsepower equation.

camino
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Homework Statement



How can I calculate the GPM (gallons per minute) of water needed to make a fountain shoot 120 feet in the air straight up? The diameter of the nozzle is 2 inches and friction is neglected. Also, what is the minimum liquid horsepower of the pump neglecting friction and assuming 100% efficiency. Please explain with formulas. Thanks.

Homework Equations



Need equations. I'm sure there is a very simple equation to calculate this since there is only 2 given values, I just can't find it.

The Attempt at a Solution



Need an equation to solve.
 
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If you use conservation of energy, what velocity should the water exit the nozzle at?
 
Not sure how to get that. I know Q = VA, so if i knew the velocity I could get Q but not sure how.
 
camino said:
Not sure how to get that. I know Q = VA, so if i knew the velocity I could get Q but not sure how.

Right so if you consider the kinetic energy of the water leaving the nozzle is being converted into the gravitational PE to each 120 ft. you will be able to get the velocity.
 
I don't know what that equation is though.
 
camino said:
I don't know what that equation is though.

Do you know what the equations are for kinetic energy and potential energy?
 
KE = 1/2 mv^2
PE = mgh
 
camino said:
KE = 1/2 mv^2
PE = mgh


and if you put them equal to each other, can you get the velocity?
 
Sure, but what do I use for m?
 
  • #10
camino said:
Sure, but what do I use for m?

You don't need 'm' :wink:
 
  • #11
I see. So I got 88 ft/s for my velocity. Now Q = (88 ft/s)([PI x {2in/12}^2] / 4) = 1.9198 x 60 sec = 115.1917 ft/min? How do I get to GPM?
 
  • #12
Nevermind, I figured it out. So I got 861 GPM. Now I need to figure out the liquid horsepower. I have the equation LHP = (Q x HP) / 3960. Not sure what to use for HP.
 

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