Compressed Air Pressure Drop Across a Restriction

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Discussion Overview

The discussion centers on the pressure drop of compressed air as it flows through a bell reducer from a larger diameter pipe to a smaller one. Participants inquire about the relevant formulas for calculating pressure drop under varying flow conditions and seek resources for understanding the physics of compressed air in industrial systems.

Discussion Character

  • Technical explanation
  • Homework-related
  • Debate/contested

Main Points Raised

  • One participant requests a formula for the pressure reduction when compressed air flows from a 3" diameter pipe through a 1.5" diameter pipe.
  • The same participant asks how the pressure drop would change if the flow rate (cfm) were doubled, seeking a formula for this relationship.
  • Another participant suggests a textbook that may help, but it is noted that the publication primarily addresses liquid fluids.
  • Some participants discuss whether the principles governing liquids and gases are the same, with references to the applicability of Crane Technical Paper 410 to gas flow.
  • There is an acknowledgment that Crane TP 410 is a significant resource for fluid flow in piping systems, including gases.

Areas of Agreement / Disagreement

Participants express differing views on the applicability of certain resources to compressed air systems, with some asserting that the suggested publication is relevant while others question its focus on liquids versus gases. The discussion remains unresolved regarding the specific formulas for pressure drop and the relationship with flow rate changes.

Contextual Notes

There are limitations regarding the assumptions made about fluid dynamics in different contexts, and the applicability of the suggested resources to the specific case of compressed air is debated.

SteveRomero
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I would like the formula that describes the reduction in pressure that results when a constant flow (cfm) of compressed air travels from a 3" diameter pipe through a bell reducer that provides a smooth transition to a 1.5" diameter pipe.

Also, in the same piping configuration as described above, if the pressure drop is X psid acress the reducer, what will the pisd be if the cfm were doubled? What is the formula for this relationship as well?

Is there a textbook that is available for non-engineers that describes the physics of compressed air in industrial compressed air systems?

Thanks a million.
 
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SteveRomero said:
Is there a textbook that is available for non-engineers that describes the physics of compressed air in industrial compressed air systems?

This is probably your best bet:

http://www.flowoffluids.com/tp410.htm

CS
 
Last edited by a moderator:
Thanks . . .
. . . CS, for your help. The publication that you identified appears to be specifically for liquid fluids . . . I need compressed air information. Do both liguids and gases follow the same physics?
 
Hi Steve,
The book stewartcs points out (Crane technical paper 410) is the bible of the industry. Process work throughout industry relies on it for fluid flow through piping systems. The paper specifically calls out where it is applicable and where not, so yes, it's applicable to compressed gas systems.
 
SteveRomero said:
Thanks . . .
. . . CS, for your help. The publication that you identified appears to be specifically for liquid fluids . . . I need compressed air information. Do both liguids and gases follow the same physics?

TP 410 does include gas flow as well as Q pointed out. It would be a great place for you to start.

CS
 
Thanks again. Crane TP 410 is where I will begin my search.

Steve
 

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