Sinopsis
Nearly everyone is familiar with "squirrel cage" fans found in home heating, air conditioning and ventilating systems. The squirrel cage is just one of many forms of centrifugal fans and blowers designed in a wide range of sizes for many different applications. Smaller fans appear on the market from time to time as surplus or salvage, some of which may find practical use in home shop applications. It certainly makes little sense to construct a fan for a special purpose if one is readily available at low cost. But some applications require air at high pressure and volume, and the fans and blowers usually available as surplus will probably not meet the requirements. At this point it becomes practical to design and build a fan for the job at hand.
It is not difficult to design a fan for a specific purpose when the importance of the effect of various factors is understood. Although state-of-the-art fan design has become highly technical, mainly due to advances in jet propulsion and turbine technology, you can easily design a fan to suit your specific needs. The basic principles that are discussed in this manual have remained unchanged for more than 150 years. Surprisingly, common materials and ordinary tools are adequate for construction of fans capable of delivering air at high volume and moderately high pressure. Because there are many design parameters that can be manipulated, fans can be designed to meet nearly any requirement of volume, velocity and pressure.
The most common application for a high pressure and/or high volume fan is in forcing air into a furnace or in exhausting dust and fumes. A blacksmith's forge or a melting furnace are examples of forced draft. The exhaustion of welding fumes or the collection of dust from woodworking machines or grinders can be easily accomplished in the small shop at low cost. These are areas of safety, protection and convenience that are usually neglected because a new fan capable of doing this work is too expensive. Because such a fan is seldom found used or surplus, it is worthwhile to consider building one.
This manual will show you how to determine the diameter and width of a fan wheel and at what speed to run it to achieve the desired pressure and volume. Several methods for building the wheel are discussed. The layout procedure for the scroll housing has been simplified. From the formula given for calculating the amount of power required to run a fan you will learn (perhaps to your amazement) how much work can be done by a common fractional horsepower motor. You will be shown how to build simple balancing equipment and how to use it. You will also learn how to test the performance of experimental fans with an easily built manometer and pitot tube. Only a few easily understood and applied formulae are needed to guide you. You will enjoy building several projects that will upgrade your shop and make your work environment safer and more comfortable. As in any shop activity there are dangers that may not be readily apparent. You should be aware that centrifugal force and generated air pressure puts great strain upon the fan wheel and other parts of the blower. Foreign material in the air stream or loose pieces breaking off the wheel can reach velocities of up to several thousand feet per minute. Very serious injury or possibly even death can result if persons are struck. Take all practical steps to protect yourself and others. Electrical wiring must be properly installed to avoid shock and fire hazards. Always be very safety conscious in the shop, and provide protection promptly whenever danger appears.
Content
- Chapter I: Fan Fundamentals
- Chapter II: Design Considerations
- Chapter III: Construction Methods and Materials
- Chapter IV: Fan Testing and Air Measurement
- Chapter V: Shop Fan Applications
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