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FAN FAQ TOPICS:
Why do VENTRY Fans use free-flow guards instead of solid shrouds?
The outer quarter of a propeller does three quarters of the work. Blocking the air at the tips with a solid shroud starves the prop of air and dramatically increases noise. To see for yourself, hold your hand flat near the outer edge of a running VENTRY Fan’s free-flow un-shrouded guard. As you move your hand closer to the guard, the noise level will increase. You will hear a sort of whump-whump-whump sound as the tips pass your hand, because you will be starving the prop of air! If your hand makes that big of a difference, imagine what a 360-degree shroud does!
We know the claim is often made, in regard to fans that sit near the ground, that solid shrouds improve the dynamics of a fan, entraining the air for greater air volume. The tolerances required for this theory to apply are well outside the limits of fans in this category.
To prove instead how solid shrouds DEcrease fan performance, do the same experiment as mentioned above, but instead wrap a long piece of cardboard around the guard of a VENTRY Fan. Stand in front of the fan when it is running and have someone remove the cardboard shroud. You will instantly notice a large drop in the noise level and a significant increase in the air volume!
TRUE STORY: Years ago, a competitor of ours who also manufactured fans, experimented with using our VENTRY Safety Propellers on their fans. Shortly after sending it, we got a very nasty phone call. They were mad! They said our props didn’t work at all and asked how could we claim such high CFM? James spent a minute troubleshooting, thinking maybe they had the prop on backwards, but eventually discovered that their fan had a solid shroud all the way around the guard. James asked them to try our propeller again, but this time to remove the shroud. A short time later, we received our Safety Propeller back, with a note saying essentially “Thanks, but no thanks.” James followed up with a call to find out what happened...When they removed the shroud on their fan, thereby giving the VENTRY Safety Propeller some air to push, their fan fell over backwards! They did not want to re-engineer their whole fan to handle the thrust, so nixed the idea of using our VENTRY Safety Props. |
Solid shrouds are used by other manufacturers to protect the propeller from sand blasting by rocks, dirt and sand and to prevent the ejection of these materials into the air. Giving the appearance of added safety, the solid shrouds also do little to slow down shrapnel that might be released in the event of metal blade failure.
Fire Chief magazine published an article that mentioned shrouds. See our response on the PPA/PPV page.
