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Static pressure

I have been scrounging around the internet trying to figure out exactly what static pressure is and how exactly it makes a difference on cpu coolers/radiator... so i thought ide give the forum a try...
Reply to XuraharaX
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More about static pressure
  1. XuraharaX said:
    I have been scrounging around the internet trying to figure out exactly what static pressure is and how exactly it makes a difference on cpu coolers/radiator... so i thought ide give the forum a try...

    Static pressure is the resistance of a system to air flow, usually measures as "inches of water". The higher the air flow the the higher static pressure . In other words, fans and blowers can deliver more air flow, cfm, when working against a lower static pressure. Clutter in a case and poorly directed air flow, and any other obstructions in the air flow path causes higher static pressure and lower CFM.
    Reply to jerryb
  2. Best answer
    Ok, here we go...

    Every fan has a performance curve which describes it's flow and pressure characteristics. The higher the pressure across the fan, the lower the flow through the fan and vice-versa. The pressure across the fan, and hence the flow through the fan, is dictated by the system in which the fan is installed. Things that impede airflow, such as small holes, heatsinks, filters, wires, convoluted flow paths, etc. cause an increase in the pressure required to drive a particular flow. The effect of this is that the more resistance you put in the path of the fan, the more the flow through the fan will drop.
    As for the the static pressure quoted by manufactuers- I assume this is either the max pressure the fan can deliver (ie. when flow = 0), or the pressure at the fan's design point (ie. flow = x cfm at y mm H20- or whatever other units of flow and pressure you want to use).
    Of course, manufacturers don't seem to make performance curves available to the public, and trying to work out the airflow resistance of your case or heatsink is nigh on impossible, not to mention a waste of time. What you need to know is that systems in which there is a high resistance to flow (heatsinks being a common example) will require a higher static pressure rating than systems which have a low resistance to flow (typically cases). So if you have a high resistance system, like a CPU heatsink, installing a powerful fan with a high pressure rating will ensure you get a decent airflow flow over the heatsink.

    Hope that helps...
    Reply to esuckq
  3. http://www.overclockers.com/forums/showthread.php?t=631724

    Radiators with a high fin per inch count need high CFM and pressure fans. Low FPI can run quieter fans with lower pressure ratings. Same goes with Air cooled heatsinks, but radiators come in MANY varied designs.

    Look at the watercooled solved post at the top, some of those links will really explain fans and cooling.

    Research and time, it's free.
    Reply to Conumdrum
  4. Best answer selected by XuraharaX.
    Reply to XuraharaX
  5. Cool, thanks.

    Found this recently- it explains it better than me...
    http://www.comairrotron.com/airflow_note.shtml
    Reply to esuckq
  6. Hello Friends,
    I am in bit of a confusion here. I have 2 kinds of fans used for industrial unit cooling. The current fan is nearing its obsolescence and I am looking for a new fan with same or better specifications to replace the older fans.
    Following are some specs.

    Old Fan:
    Rated Speed: 4300 RPM
    Air Delivery: 19 CFM
    Static Pressure: 0.18 inch - H2O
    Rated Current: 290 mA

    New Fan:
    Rated Speed: 3900 RPM
    Air Delivery: 19.07 CFM
    Static Pressure: 0.095 inch - H2O
    Rated Current: 260 mA

    Below is my opinion about the new fan, please correct me if I am wrong.

    Rated speed: Slower than Original fan but doesn't matter as long as CFM ratings are better.
    Air Delivery: New fan has better CFM
    Static Pressure: : I am not able to figure if the rating for the new fans is worse, same or better than Older fan given other parameters.
    Rated current: Better.

    ALso, The form, fit and function of both the fans is identical.

    Any and all the help would be highly appreciated.

    Thanks,
    Jambhu
    Reply to jambhumalamal
  7. Conumdrum said:
    http://www.overclockers.com/forums/showthread.php?t=631724

    Radiators with a high fin per inch count need high CFM and pressure fans. Low FPI can run quieter fans with lower pressure ratings.


    The problem is, high CFM fans don't have high static pressure ratings. Look at the list of fans made by Delta. The highest pressure ratings are for fans with around 60 cfm; fans with 100-200 cfm have lower, not higher, pressure ratings.
    Reply to shagbark
  8. jambhumalamal said:
    Hello Friends,
    I am in bit of a confusion here. I have 2 kinds of fans used for industrial unit cooling. The current fan is nearing its obsolescence and I am looking for a new fan with same or better specifications to replace the older fans.
    Following are some specs.

    Old Fan:
    Rated Speed: 4300 RPM
    Air Delivery: 19 CFM
    Static Pressure: 0.18 inch - H2O
    Rated Current: 290 mA

    New Fan:
    Rated Speed: 3900 RPM
    Air Delivery: 19.07 CFM
    Static Pressure: 0.095 inch - H2O
    Rated Current: 260 mA

    Below is my opinion about the new fan, please correct me if I am wrong.

    Rated speed: Slower than Original fan but doesn't matter as long as CFM ratings are better.
    Air Delivery: New fan has better CFM
    Static Pressure: : I am not able to figure if the rating for the new fans is worse, same or better than Older fan given other parameters.
    Rated current: Better.

    ALso, The form, fit and function of both the fans is identical.

    Any and all the help would be highly appreciated.

    Thanks,
    Jambhu


    It's lower static pressure. For pushing air through radiators with a high fin count, you'll need high static pressure fans. For pushing air through radiators with a lower FPI (fins per inch), then static pressure is less important, but still needed.

    It's always best to research the radiator you're using, then select fans based on their static pressure ratings, in order to get the best performance for your setup. What may work really well on one radiator, will work very poorly on another.

    Like Shagbark said. Generally, higher status pressure fans usually have lower CFM. And higher CFM fans, generally have lower static pressure.

    Have you ever seen a horsepower / torque curve from a gasoline engine? About the same thing.
    Reply to Vellinious
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