Can you calculate water pressure with just flow rate and hose diameter?

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Discussion Overview

The discussion revolves around the possibility of calculating water pressure using only the flow rate in gallons per minute (gpm) and the inside diameter of a hose in inches. Participants explore the relationship between flow rate, pressure, and other factors in fluid dynamics.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant suggests that more information is needed to calculate the pressure of water leaving the hose.
  • Another participant proposes that Bernoulli's equation could be relevant to the discussion.
  • A different participant mentions that the pressure after the water leaves the hose is assumed to be atmospheric pressure, but the pressure against a surface can be calculated using the force of the water divided by the cross-sectional area of the stream.
  • One participant discusses calculating force exerted during high-pressure water blasting, providing specific values for pump pressure and flow rate, and seeks help with back pressure calculations.
  • Another participant emphasizes the need to determine the velocity of the water to apply Bernoulli's equation, asking for the area of the nozzle.
  • A later reply clarifies that there are two nozzles, both with a diameter of 1/8".

Areas of Agreement / Disagreement

Participants express differing views on whether the information provided is sufficient to calculate pressure, with some suggesting that additional parameters are necessary while others propose methods to derive pressure from the given data.

Contextual Notes

There are assumptions regarding the relationship between pressure, flow rate, and velocity that remain unresolved. The discussion does not clarify the specific conditions under which the calculations would apply.

Who May Find This Useful

Individuals interested in fluid dynamics, engineering applications involving water pressure, and those seeking to understand the principles behind pressure calculations in practical scenarios may find this discussion relevant.

rick326
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Given only the rate of flow in gpm and the inside diameter of a hose in inches, is it possible to calculate the pressure of water leaving the hose?
I have no experience or training in this area but it seems to me that more information would be required. Any help will be greatly appreciated.
 
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it's been a while, but i believe that Bernoulli's equation could help. Check that one out
 
Without getting into very advanced fluid dynamics, it is assumed that the water pressure, after the water has left the hose, is same as atmospheric pressure.

If you are referring to the pressure of the water against a surface (as the water splashes on a surface like your hand, after it leaves the hose) then the "pressure" would be the force of the water/cross-sectional-area of the water stream (assumed to be the area of the hose?) P=F/A

From the volume flow rate (gal/min) you can calculate the "mass-flow rate" (mass/sec), and assuming all the water is stopped, the mass flow rate times the change in velocity will produce the force.
Ft = m[delta]v , so F=(m/t) x [delta]v

So, yes, the pressure of this stream of water against a surface can be calculated from the information given.
 
Last edited:
I am trying to calculate the force exerted on a body during high pressure water blasting. The numbers are 36,000psi pump pressure, 5gpm flow rate. lbs of force back pressure is the number I'm looking for. HELP!
 
You need the velocity, then you use Bernoulli's equation to find the pressure. What is the area of the nozzle?
 
There are two nozzles. Both are 1/8" in diameter.
 

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