Regenerative Blowers
Regenerative blowers are the ideal solution
for moving large volumes of air at lower pressures or vacuums.
Unlike positive displacement compressors and vacuum pumps, regenerative
blowers “regenerate” air molecules through a non-positive
displacement method to create vacuum or pressure. In the world
of air handling equipment, regenerative blowers are probably the
least understood of today’s technologies, but when system parameters
fall within the range of a regenerative blower, it can be the
most cost effective method for producing pressure or vacuum.
Regenerative blowers are also 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, as discussed below.
Regenerative blowers in plant installations
are typically in a direct drive design, versus electric motor
/ gas engine belt drive configurations. (refer photo depicting
these 2 designs). The impeller in the direct drive (sometimes
called monobloc) construction is mounted directly on the electric
motor shaft and rotates at the motor’s nominal speed, typically
2900 or 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. Some makes
of blowers have somewhat “flat” curves (Y axis =pressure
/ vacuum, X axis = scfm), while other makes have quite steep performance
curves. 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. 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 continuous
operating pressures up to 9 psig or vacuum to 14″ hg with
flows in the 200 to 250 scfm range at these points.
Most blowers are single stage as air molecules
travel around the blower housing one time and then are exhausted.
In addition to single stage units, some blower manufacturers offer
two staged blowers. Two stage regenerative blowers are capable
of providing nearly twice the pressure or vacuum of single stage
units. Two staged blowers operate much like single stage units
as the impeller strikes air molecules over and over to create
vacuum and pressure. In a staged blower air molecules will make
one revolution around the front side of the impeller. Instead
of being exhausted after the first revolution (like single stage
units), the air flow is channeled to the back side of the impeller
through internal porting. Air molecules will then make another
revolution around the back side of the impeller thus doubling
the number of times that the impeller blades strike the air molecules.
After a second revolution around the blower housing, the air is
exhausted. Higher pressures and vacuums are able to be generated
with two stage blowers since the impeller blades strike or “regenerate”
air molecules through two revolutions instead of one.
For the engineer, 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. As a “non-positive
displacement” compressor / vacuum pump, discharge air, besides
being clean, is pulsation-free, an important consideration particularly
for plant controls or instrumentation use.
The majority of blower failures are due to
improper installation and / or operation. Because there are so
few moving parts, there is not much that can go wrong. Regenerative
blowers have close internal tolerances between the impeller and
housing, and it is important to not allow foreign material 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. A filter should
always be purchased with a blower to prevent debris from entering
the blower. A 10 micron filter is usually adequate to prevent
such a failure from happening. Over pressurization can also cause
a catastrophic failure. Some blowers can be “dead headed”
(zero airflow through the blower) while other models (usually
¾ HP models and above) must have air passing through the
blower to cool it. If air does not pass through the blower, heat
will build up causing the impeller to expand at a faster rate
than the blower housing. Eventually the impeller will lock up
with the housing causing the blower to fail. A relief valve (either
vacuum or pressure) will prevent over pressurization and will
allow air to pass through the blower. Most blower manufacturers
offer filters and relief valves as accessories for their blowers.
Regenerative blowers are used in a broad range
of applications. These include: pneumatic conveying, sewage aeration,
vacuum lifting, vacuum packaging, packaging equipment, printing
presses, aquaculture/pond aeration, spas, dryers, dust / smoke
removal, industrial vacuum systems, soil vapor extraction, and
chip removal for engraving equipment. Anywhere high airflow and
low vacuum / pressure is required, regenerative blowers are an
ideal solution as a properly installed blower will provide years
of service free operation.
This article was provided by FPZ Inc.