# what makes a static pressure fan a static pressure fan

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July 8, 2014 10:20:15 AM

Ok..I know the difference between a static pressure fan and an airflow fan but what i was wandering is how exactly is a SP fan design different from a AF design. Ive looked all over the net and have not found anything that explains this particular infromation. Its not that its an important bit of information but i was just kinda of curious if anybody (other then the people that make the things) had any ideas.
July 8, 2014 10:39:54 AM

A static pressure fan has big wide fins that go almost all the way to the edge of the fan shroud. Thus creating more static pressure by not allowing air to escape past the blades when pushed up against a radiator. An airflow fan will have more smaller fins with more space between them.
Check the pics of the 2 http://pcpartpicker.com/p/2yM4CJ
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July 8, 2014 10:45:24 AM

I had to Google it to explain it properly. Static pressure is the measured force exerted on a still surface not resultant from the velocity of the moving air. Velocity pressure is the force directly resultant from the moving air.

Total pressure is the sum of velocity pressure + static pressure.

Static pressure is exerted equally in all directions, including TOWARDS the airflow.

In the HVAC industry, if static pressure is too high in a system, ductwork or other components may "whistle" or be excessively noisy or loud. By the same token, a certain amount of static pressure is necessary to deliver airflow properly.

The best explanation I can think of right now would be as follows:

If you were delivering 100 cfm from computer fan through a huge duct the size of a car, you wouldn't be able to effectively deliver the air through a vent or register because you would have very little static pressure.

If you delivered the same 100cfm through a duct approximately the size of the computer fan, you would have better static pressures and more effective delivery.

Yet again if you delivered 100cfm through a drinking straw, it would blast out the other end, probably be noisy, and indefinitely make the fan work harder due to higher static pressure.
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July 8, 2014 10:48:34 AM

So as the above poster said - as the fins are closer together and therefore doesn't let as much escape backwards (static pressure is exerted in all directions as previously posted), which results in higher SP.
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