1. Despite the fact that many in industry use the terms interchangeably, technically there’s a difference between compressors and fans and blowers.
In short, compressors pressurize gases within controlled volumes to ultimately facilitate some type of work. Fans move large gas volumes with slight pressure increase. Blowers move large gas volumes with moderate pressure increase. Further differentiation is made between blower subtypes, as regenerative blowers are generally applied in designs needing high-pressure movement of low airflow, and centrifugal blowers are generally for low-pressure movement of large airflow.
2. Most blowers use one of four motor types — and that largely dictates performance. These include:
• Brushed ac and dc motors that come in the form of PMDC motors, shunt-wound motors, series-wound motors (also called universal motors), and compound-wound motors. These motors are cost effective and simple to control — so are particularly common in blender, grinder, and home-appliance applications.
• Switched-reluctance motors. These blower motors are most common in HVAC blowers, vacuum and cleaning appliances, and industrial material-handling applications that need clean and reliable blower operation.
• Brushless motors that incorporate permanent magnets — also called EC motors for the way in which they’re electronically commutated. These blower motors excel where designs need high efficiency, long life, and airflow adjustability — to optimize turn down for top blower performance, for example. Brushless blower motors first became common in transportation applications — those fans, pumps, and motors on heavy-duty transports and other commercial vehicles. Now they’re finding use in food and beverage, business-machine, and even medical designs.
• Induction motors — or (in the context of blowers in particular) often called by the more playful squirrel-cage motors (to avoid confusion with inducer-blower products). In fact, these motors are the most common used in blowers today, as they excel in high-horsepower blower and cooling-fan applications.
3. As in other industries, permanent-magnet brushless motors are on the rise in an array of fan, blower, and other fluid systems.
That’s because these brushless blower motors are increasingly large — no longer limited to fractional-horsepower applications. In addition, because the current-carrying coils are on the stator, heat dissipation is also simpler. Most importantly though, today’s cost-effective electronics means that permanent-magnet brushless blower motors are in many cases cost-competitive with comparable brushed motor blowers — especially when long-term cost of ownership is taken into account.
4. VFDs paired with ac motors greatly improve efficiency — as well as fan and blower performance.
Recall that blowers incorporating squirrel-case motors are sized for peak demand — so are by definition over sized for average blower operating conditions. That means the motors run inefficiently unless there’s some speed control to optimize flow for actual application conditions. This is where VFDs can control blower-motor speed to most efficiently satisfy airflow requirements. In fact, this core VFD function relates to a concept applicable to all blower motors, no matter which motor type they employ — the concept of turn down.
Turndown is the operating range of a blower or blower system — an expression of its ability to reduce airflow rate. Most often it’s expressed as a ratio of the blower’s minimum airflow to its maximum. Sometimes it’s calculated as the difference between maximum and minimum airflow rates, then divided by maximum airflow rate.
5. Regenerative blowers are for very specific applications.
Recall that in regenerative blowers (unlike centrifugal blowers) the fluid inlet is parallel to the outlet with both perpendicular to impeller rotation. Vanes push air along arcs parallel to the blower-body circumference — even as centrifugal forces push air between impeller vanes outward. Airflow then progresses to the next vane’s root for more re-circulation — ultimately for a spiral airflow path subject.
6. Mufflers, valves, and diverters are core to blower system design.
Rather than afterthoughts, these subcomponents are essential and often quite sophisticated. Just consider diverter valves that can automatically change piping from suction to pressure (and vice versa) to impart blower versatility. They’re especially useful for replacing two blowers with one on installations having intricate piping — as in vacuum-based material and part handling, air tables, and pneumatic tube systems.t to constant acceleration (and pressure buildup).
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