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Free-Flow Guards vs. Solid Shrouds
Click here for more advantages shown in the above llustration
It is important to know that in order to push a lot of air, a propeller has to have a lot of air reach it! Supplying more air TO the propeller simply results in more air being pushed BY the propeller.
When a VENTRY Fan runs, its propeller pulls air in from the back, the sides, and even the outer front edges of the guard -- then it shoots that air forward in a consistent, central stream of air. The majority of the propeller’s air supply reaches the propeller from the sides, through the open-flow guard.
To demonstrate the noise problem for yourself, start a VENTRY Fan and hold your hand perpendicular to the propeller. As your hand approaches the guard, lay it flat against the side of the wire guard. You will hear a sort of “whump-whump-whump” sound as the propeller tips pass your hand. What happens is that every time the propeller tips pass your hand, they make a noise. It is prop starvation! If your hand makes that big of a difference, imagine how noisy a solid shroud clear around the propeller would be! For more on noise, click here.
The false claim is often made that solid shrouds improve the dynamics of a fan by entraining the air flow as it goes through the shroud. The tolerances required for this theory to apply to conventional PPV Fans are well beyond the capabilities of ppv fan manufacturers! Entrainment does happen during PPV, but it is through the entry, not the propeller.
To prove instead how solid shrouds DE-crease fan performance, wrap a long piece of cardboard around the guard of a VENTRY Fan to simulate a solid shroud. Stand in front of the fan when it is running and have someone remove the cardboard shroud. You will instantly hear a huge decrease in noise and feel a big increase in the air volume!
So why do other fans have solid shrouds? One reason solid shrouds may be used by other manufacturers is to prevent the propeller from being sand blasted by rocks, dirt and sand and to prevent the ejection of these materials into the air stream. Solid shrouds give the (false) impression of safety too; unfortunately, they do little to slow down shrapnel, released in the event of metal propeller blade failure.