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Anybody with understanding of how Air pressure regulators function?

  1. Mar 27, 2008 #1
    As title dipicts I'm wishing to understand the relationships between CFM and PSI in regards to Air Regulation.

    For example lets say I had a compressor tank with a compressor connected to it, to fill it to 200 PSI. I connect an X diameter Air line to an air regulator, and than have its output just an open X diameter Air line.

    So my question is how can I control both variables. How could I have lets say a high flow rate, but lower maintained pressure. Or vice or versa, how could I have a low flow but at high pressure.

    What I understand is that an air regulator (by some means) reduces the air pressure (PSI) by having a preset (spring rate) spring that opens after what ever you set the pressure tension bolt at(or what ever means the system uses to change spring reaction/travel). What I don't see is if the CFM would change based on what PSI the regulator is at. Also another thing I don't understand is how the X diameter line falls into play. I would think the larger the line, the higher the flow. Pressure would be the same but the tank would empty faster. How can I understand this fine line and learn how to balance those numbers.

    Hypothetically lets say I know how much CFM I would like to generate, and I know at what PSI I want the CFM to be at. So in the end how would I control both those variables.

    Hopefully me spelling it all out will avoid missunderstandings and replies that wouldn't hit the nail on the head and end up not giving me the exact answers or where to look for them.

    Thanks for all those who read this short "story" and also to those who may reply!
  2. jcsd
  3. Mar 27, 2008 #2


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    Regulators operate on a balance of forces combined with a particular flow geometry. Whether that includes a spring or a compressed air volume doesn't matter.

    Here's a pretty good paper describing the theory:
  4. Mar 30, 2008 #3
    Excellent, thanks! That covered most of what I needed to know about the pressure regulators. I didn't end up seeing anything about how that changes how much air is flowed. It limits the pressure of the air comming out, so wouldn't that also mean the amount of air flowed would be substaintially less? Or because its compressed air, if its let out at 8psi, it will expand to a volume based on the compression level of 8psi?

    Does anybody have any info on ways of compairing how CFM and PSI react with varrying sizes/diameter of piping or lines? For example, If I had a 1/2 inch diameter line, how much CFM could I flow through it. Also, how does the pressure its compressed at factor into this.
  5. Mar 30, 2008 #4


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    The amount that you can flow through a given pipe/opening will be totally dependent on the delta P across the thing you're flowing through. In the case of a regulator, you have to look at the specific model's engineering data to see the flow characteristics. There is no one set way that handles all different models.

    This does not hold true for pipe flows though. If you do a search on this topic, there are a number of posts by Q_Goest in which he has posted a PDF of some very well known flow calculations.
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