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This may seem like an odd question, but I'm trying to figure this one out.

I'm currently looking to purchase a "VGA Silencer" from Artic Cooling for my ATI 9800Pro. The version for that card is "Version 1", now at "revision two". But you can still find the revision 1 card for sale from most distributors.

Besides the fact that the "rev1" cooler has a blue fan and "rev 2" is a nice black, I also noticed that the long fan blades curve INTO the spin on the "rev 1" and AWAY from the spin on "rev 2".

"Revision 1":


"Revision 2":


(Notice the direction of the fan blades. The fan spins clockwise on both.)

You would *think* that the rev 1 fan would be better, but the only difference between the two cards given on ATI's website is that "rev 2" is now compatible with their "All In Wonder" cards. No explaination as to why they changed the direction of the fan blades.

So, can anyone explain this to me? Is the "rev 2" fan actually better than the "rev 1"? Too weird.

If you stand on the other side of the card you'll notice that everything is symetrical and both cards work the same.

That makes abosultely no sense. Please explain.

The cooler mounts one way and one way only. Doesn't matter "from which way you look at it".

I have one of the first version coolers, and it didn't put out a whole lot of air. My guess is the second ver has enhanced airflow, and you don't need to be concerned at all about what direction the fan rotates. Worry if you get the power wires backwards.

Thanks. But things just got a little more confusing.

Reasearching on Artic Cooling's website, I noticed that revision "3" of the "VGA Silencer" has the old blue fan with blades that angle "into" the spin. Question is, is the "VGA Silencer rev 3" older than the "ATI Silencer rev 2"???

Also, it does indeed matter very much which way the fan spins, since "counter-clockwise" would suck air in from the outside and blow the heat *into* your case. AC says all their fans spin clockwise.

Sorry missed this point in my 1st post.

I do not think think it's possible for Rev2 fan to be rotating CW, if it did the fan baldes would have no effect. They must spin in the direction of the curvature of the baldes.

You are correct if you mean to say the fan/airflow system is DESIGNED to suck air across the cooling fins and out the top open face. So once again the REV1 and 2 ARE equivalent IF Rev2 rotates CCW (but it must, there is NO way any engineer could keep his job if this thing rotates CW!). I'm certain REv2 must rotate CCW. If it doesn't do not buy it, it's a complete failure of design.

Cheers, and sorry for the confusing post previous.

The fan appears to be a simple "centrifugal fan". Notice the blades are flat.
High pressure air at the ends of the blade created by centrifugal force and trapped by the blower housing is forced over the heat sink.
Air is drawn into the housing from the center hole at the base of the blades (low pressure created by centrifugal force).
Air flows in the same direction regardless of fan direction.

The only thing that changed on the blades is the Revision 1 the blades are curved CW and the Revision 2 curved CCW.
Revision 2, housing and blades appear to be a more efficient design. IMHO.

From AC's website FAQ:

Q: Which direction should the fan rotate?
The fan of all ATI or NV Silencer coolers should rotate clockwise.

http://www.arctic-cooling.com/vga2.p...6&data=6&disc=

So you see my puzzlement.

That was my point from the beginning, that the blade curvature changed w/o reason.

Curving the blades "away" from the direction of the flow would seem to push "less" air, not more. On what basis do you belive the second design to be more efficient?

Lots of things to consider when using forward-curved (FC) and backward-inclined (BI) blades, housing design, fan speed and many more.

Check out this artical.

http://www.yaskawa.com/site/Industri...t&fileFormat=B

"Centrifugal Fan or Blower. The centrifugal fan consists of a wheel with small blades on the circumference and a shroud to direct and control the air flow into the center of the wheel and out at the periphery. The blades move the air by centrifugal force, literally throwing the air out of the wheel at the periphery, creating a suction inside the wheel. The basic types of wheel blades in centrifugal blowers are forward-curved (FC) and backward-inclined (BI). A centrifugal blower with forward-curved blades has blades that are curved in the direction of wheel rotation and, is primarily an impulse device. It accelerates the air to a high velocity, while rotating at a speed that is usually low compared to that of a backward-inclined blower. The forward-curved type is known as a "volume" blower, and is more common because it delivers the greatest air volume in relation to blower size and speed. It has static efficiency in the range of 60 to 68%."

"The backward inclined blower wheel design has blades that are slanted away from the direction of wheel travel. The term applied to this type of blading is BI or backward inclined. (An AF fan, or air foil fan, is a subset of the BI fan with, as the name implies, more efficient fan blades.)
The performance of this wheel is characterized by high efficiency, high cfm and its rugged construction makes it suitable for high static pressure applications.
The maximum static efficiency of the BI wheel is approximately 75 to 80 %. When a BI fan is selected to handle a given air quantity, it must be operated at approximately twice the speed of a similarly selected FC fan. In spite of this, the horsepower requirement of the BI fan is less, making it a more efficient design."

Wow, that article really more than covers the subject! Very interesting.

Thanks. (though my curiosity does still wonder "why" BI moves more air.)

:bounce: