How fast will 120 psi travel through a 3 inch tube in mph?

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Discussion Overview

The discussion revolves around calculating the speed at which air at 120 psi would travel through a 3-inch tube, focusing on the relationship between pressure and flow. Participants explore concepts related to pressure gradients, flow dynamics, and the influence of system design on speed calculations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant emphasizes that 120 psi is a measure of pressure and does not directly indicate flow speed, suggesting that flow requires a pressure difference to occur.
  • Another participant proposes that the term "pressure gradient travel" might be more appropriate than "flow," noting that pressure gradients can travel at sonic speeds.
  • A participant mentions the importance of system design, such as the size of the reservoir and valve, in determining the effective speed of the air moving through the tube.
  • One participant suggests using the speed of sound as a starting point for estimating the speed, while acknowledging that specifics of the valve and container will affect the actual speed.
  • A casual remark about a potato gun is made, possibly indicating a practical application or analogy related to the topic.

Areas of Agreement / Disagreement

Participants do not reach a consensus on how to calculate the speed of air through the tube, with multiple competing views on the definitions and factors influencing flow and speed remaining evident throughout the discussion.

Contextual Notes

The discussion highlights the complexity of flow dynamics, including the need for pressure differentials and the influence of system components on speed calculations. There are unresolved assumptions regarding the specifics of the setup and the definitions of terms used.

Who May Find This Useful

This discussion may be of interest to individuals exploring fluid dynamics, engineering applications involving pressure systems, or those seeking to understand the relationship between pressure and flow in practical scenarios.

Joey Bradshaw
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I need help finding out how fast 120 psi will travel though a 3 inch tube in mph. My partners are counting on me and thanks to anyone that can help me.
 
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What do you know and what part are you having trouble with?
 
Joey Bradshaw said:
I need help finding out how fast 120 psi will travel though a 3 inch tube in mph. My partners are counting on me and thanks to anyone that can help me.
When you say 120 PSI you are talking about a pressure. Flow is a different variable. For instance you could say I have a tube with 120 PSI in it, say 3 inch diameter and 4 feet long and it is enclosed so that is the total volume and we open a valve quickly to another tube say also 3 inch diameter and 4 feet long and at a vacuum level of 1 millitorr, you could do a speed calculation but just a tube with 120 PSI in it does not indicate flow so the speed would be zero there.

Also, for there to be a flow, there has to be a place with say 120 PSI and another place with say 100PSI, that would flow from high to low PSI and the difference of 20 PSI would be the variable to use to calculate air velocity, or water or oil, whatever.
 
Last edited:
"Flow" may not be the proper term, although the air in the pipe does move as it is compressed. Maybe "pressure gradient travel" would be a better term. Not a big deal in any case. First, be aware that pressure gradients travel at roughly sonic speeds so the time intervals will be quite short. And there will be a slight error due to the time it takes for enough air at 120 PSI to fill into the pipe to pressure it up. This can be minimized by using a relatively large reservoir and valve vs. the diameter of the pipe. For example, 1/2" tubing and a 2" ball valve on a 60 gallon reservoir. That's all I can come up with right now.
 
Potato gun?
 
It's probably going to depend on details of your valve and container, but for a ballpark estimate, you could start with the speed of sound.
 

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