Flow Rate in Compressed Air System

[bghanson]

I am trying to determine what the flow rate of compressed air would be in the event a pipe or hose is completely severed. The idea is to install a shutoff valve upstream that will activate when the discharge flow rate nears this calculated maximum flow rate. This will hopefully keep someone from being beaten severely by a 1" rubber hose whipping around the room.

The system consists of a 3" copper main. A 1" copper line will tee off the main and feed the 1" hose. The system pressure is 120 psig. Our facility is at an elevation of 4500 feet above sea level.

I have tried several methods to estimate the flow rate and have seen widely varying results. Any help is appreciated!

 

[Montemayor]

In case Milton Beychok doesn't read this thread and responds directly, you should go to his Website at:

http://www.air-dispersion.com/

and there you will find the applicable equation for an accidental release of your compressed air to the atmosphere. If you luck out and Milton reads this thread, I'm sure he'll be of great help in guiding you to a solution. He not only knows his stuff, he is a great teacher and a great help to other engineers.

Good luck.

 

[unclesyd]

1” hose puts you on the upper shelf, a little more expensive. Most excess flow valve suppliers have methods for calculating the type valve needed. We used 3 times the normal flow on a hose to take care of surges and pressure fluctuations.

In addition to the above advice you might want to take a look at the standard listed below.
I recently saw a citation that mention this standard as guide.

http://www.astm.org/cgi-bin/SoftCart.exe/DATABASE.CART/REDLINE_PAGES/F1793.htm?E+mystore

 

[Latexman]

bghanson,

A good reference for your air flow problem is Perry's Chemical Engineers' Handbook, 7th Edition, page 6-23, section titled "Adiabatic Flow with Friction in a Duct of Constant Cross Section". It even has an example worked out. There are other references, if you can't access a Perry's.

I would treat the 3" main as an unlimited reservoir supplying the 1" pipe and line.

The lowest maximum flow would be if the hose broke right at the very end. Not the end where the hose is connected to the 1" pipe, the other end.

Though, unclesyd's advice seems very practical and probably more conservative than mine!

Good luck,
Latexman