Types of blowers and industrial fans – applications and industries a thomasnet buying guide gas under a dollar

Blowers are mechanical or electro-mechanical devices used to induce gas flow through ducting, electronics chassis, process stacks, etc.–wherever flow is needed for exhausting, aspirating, cooling, ventilating, conveying, and so on. See also Fans. Key specifications include intended application, blower type, port design, as well as the parameters of flow capacity, electrical ratings, and dimensions. Blowers cool electronic enclosures, induce drafts in boilers, increase airflow on engines, and are configured in a variety of designs such as centrifugal flow or rotary lobe styles. Motors usually drive blowers, though they can be powered by other means such as engines. Often used interchangeably with “Fans,” blowers are defined by the ASME as having a ratio of discharge pressure over suction pressure between 1.11 and 1.2, while fans are defined as anything below this ratio and compressors are defined as anything above it. Some makers of portable fans refer to their units as blowers even if they do not necessarily conform to the ASME distinction, which applies to permanently installed industrial process equipment. Another kind of blower is the mobile or hand held device used for moving fallen leaves.

Types of Blowers Centrifugal Blowers Centrifugal blowers use high speed impellers or blades to impart velocity to air or other gases. They can be single or multi-stage units. Like fans, centrifugal blowers offer a number of blade orientations, including backward curved, forward curved, and radial. Blowers can be multi- or variable speed units. They are usually driven by electric motors, often through a belt and sheave arrangement, but some centrifugal blowers are directly coupled to drive motors. Fan speed can be changed to vary flow rates by resizing sheaves, using variable speed drives, etc., but dampers are even more common as a means of adjusting flow. Fan affinity laws dictate that a percent reduction in speed will produce a like reduction in flow.

Positive Displacement Blowers Positive Displacement blowers are similar in principle to positive displacement pumps in that they use mechanical means to squeeze fluid and thereby increase pressure and/or velocity. Centrifugal designs, on the other hand, impart velocity and pressure to media by flinging them outward with impellers. Among positive displacement blowers, the Roots, or rotary lobe, type is common, which uses two counter-rotating lobed rotors to move fluid through the blower, much the way a gear pump moves oil or other viscous liquids. A cutaway blower (below) shows one of the two rotors. Positive displacement lowers are often driven by direct-coupled electric motors but they can be driven by gas engines, hydraulic motors, etc. in unusual circumstances.

Applications and Industries Centrifugal blowers are routinely used for combustion air supplies, on cooling and drying systems, for fluid bed aerators, with air conveyor systems, for dust control, etc. Positive displacement blowers are also used in pneumatic conveying, and for sewage aeration, filter flushing, and gas boosting, as well as for moving gases of all kinds in the petrochemical industries. Centrifugal blowers are often built as close-coupled units, meaning that the impeller wheel is not supported by independent bearings but is cantilevered on an extension of the motor shaft and relies on the motor bearings for support. Close coupled mounting dispenses with the need for shaft couplings. Other arrangements cantilever the wheel off pillow block bearings, such as designs that use belt drives. Blowers are sometimes stepped up from motor speed, but are just as often stepped down or 1:1 ratios. The centrifugal blower outlet is usually arranged tangentially to impeller rotation and can be specified usually in one of eight angular orientations with respect to the direction of the blower wheel rotation, making for sixteen possible arrangements of rotation and discharge orientation in 45 degree increments. Industry practice specifies impeller rotation either as CW or CCW as viewed from the drive end—usually the motor end—of the unit. On smaller centrifugal blowers the housings can often be rotated through a full circle to permit any angle of discharge. Rotary lobe blowers usually orient the input and output ports in line, due to the design of the blower.

Considerations Blowers are specified on the basis of pressure and flow rate. As mentioned, the ratio of system inlet pressure and outlet pressure determines whether a fan or blower should be picked according to strict definition, although the terms are sometimes used synonymously. Where higher pressures are needed, a designer may have to select a positive displacement machine over a centrifugal type. Manufacturers often publish fan performance curves or similar charts which help the designer to narrow his choice to one or several models that match requirements. The chart at right is fairly common among blower makers. System designers decide the flow rate and pressure needed and add additional capacity to overcome frictional losses in the systems due to ducting, piping, etc. They can select materials or coatings that combat the effects of corrosive media. Most blower capacity charts are based on standard temperature and pressure, ie, 70 degree F air at sea level. Where design conditions are different, designers can apply correction factors which size the blowers based on actual conditions.

Blower Type Checking centrifugal or positive displacement will separate search results into the two main blower types. Another few boxes can further refine the blower type, that is, picking rotary lobe, rotary vane, Roots, etc. will narrow the results to positive displacement machines of these specific types. There are some non-industrial blowers which can be selected here as well, leafblowers, for instance.

Blades Backward inclined and forward curved refer to centrifugal blowers and relate to the orientation of the blades. Forward curving blades move larger quantities of air than backward inclined blades do, albeit at lower pressures. Backward inclined blades tend toward higher efficiencies. Radial blades also relate to centrifugal units, representing simple paddle type construction with no backward or forward inclinations. They can be self-cleaning, an important consideration for blowers handling dirty media. Airfoil blades also apply to centrifugal blowers.