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Regenerative Blowers

October - 2014
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Regenerative blowers are the ideal solution for moving large volumes of air at low pressures or vacuums.  As such, these units are found in many finishing shops, primarily as solution agitators, but also for blow-off  / drying,  as well as fume extraction. Unlike others members of the  air moving equipment family (compressors, fans, vacuum pumps), less is known about their operating principles, capabilities and maintenance needs.

Operating Principles

Regenerative blowers are also sometimes called side channel blowers or ring compressors, terms that refer more to their physical construction. The more common name regenerative comes from their basic operating principle.

The impeller is mounted directly on the electric motor shaft and rotates at the motor’s nominal speed, typically 3500 rpm. The impeller consists of numerous radial blades on the circumference of the impeller. The number, size and angle of these blades contribute to the pneumatic performance (flow vs. pressure /vacuum) characteristics of each blower.  The impeller spins within a housing that consists of an inboard and outboard “channel” (hence the term side channel blower). As the impeller passes the inlet port, air is drawn in.  As the impeller rotates, air is captured between each blade on the impeller and is pushed both outward and forward into the channels.  The air then returns to the base of the blade. This process is repeated over and over as the impeller spins.  It is this regeneration that gives the blower its pressure / vacuum capabilities and its more common name. In essence, a regenerative blower operates like a staged reciprocal compressor and while each blade-to-blade regeneration “stage” results in only slight pressure increases, the sum total, from air entry to outlet can yield, in some makes, continuos operating pressures up to 9 psig or vacuum to 14” hg  with flows in the 200 to 250 cfm range at these points.

Operation & Maintenance

For the shop operator, one of the biggest benefits of a regenerative blower is, by virtue of its fundamental design, its lack of maintenance / monitoring requirements.   The impeller is the only moving part;  it does not come in contact with the housing channels and is, therefore, “wear-free”.   Self-lubricated bearings are the only wearing parts.  Regenerative blowers are oilless and have no complicated intake / exhaust valving. Furthermore, most blower makes can be mounted in any plane and, with dynamically balanced impellers, generate little vibration. While “motor-less” (bare-shaft) regen blowers exist, most applications are served by direct-drive design, hence no pulleys / belts. 

Due to this basic construction, regenerative blowers are durable and virtually “maintenance-free”. While warranties vary from manufacturer to manufacturer, it is not unreasonale to expect 70-80,000 hours of operational life from a regen blower.

 Every shop operator, despite the cleanliness of his operation, would recognize the need to filter equipment like this. Regenerative blowers have close internal tolerances between the impeller and housing, and it is important to not allow foreign material, including liquids, to enter the blower.  Debris that is ingested by a blower can cause a catastrophic failure as it may become wedged between the impeller and housing which will cause the blower to lock up.  Most manufacturers will specify / provide the appropriate filter for their blowers, but typically ratings of 10m   with 99% effeciency are used, with filter area appropriate to the blowers flow capacity.

Outside of  ingest of foreign material, including liquids (avoidable by using a check valve, if needed), there are really only 2 other ways to damage these units—and both are related to heat.

While most units are installed originally with the correct filter, maintenance of those filters is sometimes overlooked, leading over time to a false resistance, limiting the air intake or “starving” the blower. This is one way excess heat is generated.

The second condion is also related to inadequate air supply, but for a different reason.. Some smaller blowers are able to operate in a “dead-head” (max pressure / 0 flow) condion, but the majority of units require some air to be going through the blower at all times for cooling. Regenerative  blowers are fixed displacement---as long as the impeller spins at X rpm, the blower wants to put out Y flow. However, this flow decreases as the blower works against a positive (pressure) or negative (vacuum) head. Some blower manufactures will offer up to 4 different horsepower motors on one basic blower. This  has no effect on flow—only the pressure/vacuum (or “work”) capacity. If the pressure capacity is exceeded, in this case approx. 3.9psig (108”H2o), the amount of air passing will not be adequate to prevent the blower from over-heating. In this condition, the motor is also exceeding its full load amperage, contributing additional heat.

This over-heating can ultimately lead to the impeller expanding into the housing, resulting in a locked blower. Some users confuse the squealling evident during this condition as a “bad bearing”, when, in fact, it is the impeller coming in to contact with the housing. The impeller, once cooled, will not automatically shrink back to its proper size  and, depending on time / severity, will score itself and, possibly, the housing. Often times this scoring can be buffed out and the blower can be returned to service, with most of its original  flow/pressure capacity.  It is for this second reason, excess heat generated by excedding the blowers pressure/vacuum capacity, that users are encouraged to use relief valves, which can be set to open at the blower’s maximum pressure / vacuum.

 Of course, many agitation applications should be “fixed backpressure”, with no change in solution type or depth. However, one kinked line, a clogged air outlet or an increase in solution depth (planned or unplanned) could lead to an expensive blower overhaul or replacement, avoidable by using a relief valve (n.b.: the relief valve will not sense a clogged intake filter. There are, however, relatively inexpensive pressure differential sensors that can be used with the intake filter if regular visual inspection difficult or unreliable). 

Dedicated Regens Versus Central Compressed Air

As already discussed, regenerative blowers are the most efficient solution when high air flows are needed, but at relatively low pressure (< 9psig). Some operators continue to use their “shop air” as the air source for these low pressure/high flow applications, such

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as agitation / blow-off. While this initially seems the “low cost” way to go by using an existing compressor versus a “dedicated” regen blower, this is a highly ineffecient use of a typical industrial compressor. These compressors have much greater pressure capacity (normally to 175psig), but their air delivery, versus regen blowers, is relatively low. For example, depending on actual electricity rates, using a 15hp. compressor, 4,000 hours/year to deliver approx. 80cfm @ 3.0psig (a typical range for agitation) could require in excess of $2,500 in operating costs. This same air delivery could be provided at about one-fourth of this electrical power consumption by a 3.0hp regen blower and would pay for itself in less than 7 months.

Regenerative blowers are used in many different applications---packaging / printing equipment, vacuum hold-down, industrial vacuums, etc. Typical metal finishing applications can actually be considered “easy” i.e., straight-forward, typically fixed air demands, operating in a monitored environment. Selecting the correct blower, with proper installation and use of appropraite accessories, should give the shop operator years of trouble-free service.

Article providede by FPZ, Inc., a 35 year-old manufacturer of high performance regenerative blowers.

For further information, including FPZ’s “Tank Agitation” sizing brochure, please contact:

FPZ, Inc.

Metals / Finishing  Marketing

150 N. Progress Drive

Saukville, WI  53080

Tel.: (262) 268-0180

Fax: (262) 268-0415