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| The use of Pressure
Blower-IN-SERIES has these specific
advantages:
For instance, where two blowers are operating in series and one breaks
down, the other may
be able to "limp" the system along while the necessary maintenance is
performed.
Having on blower continue in operation can often allow limited
production while the other is being
repaired. Also, there are cases where having one blower continue in
operation could prevent or
at least minimize system or equipment damage from such things as high
temperature of
contaminated airstreams.
Another advantage of blowers in series is that of the available space.
If system must be
expanded and increases the CFM requirements, the allotted space for the
original blower may
not be large enough for a single large blower, but might be large
enough to install two smaller
blowers in series to obtain the necessary pressure.
One more potential advantage for series operation is the likelihood of
initial cost savings.
Although each case must be evaluated individually, it is often more
economical to select two
"smaller" blowers with their respective smaller motors and drives than
to select one "larger"
blower to do the job.
Series connected blowers are those which have the outlet of the one
blower exhausting into the
inlet of another blower. By connecting blowers in such a manner, high
static pressures can be
attained. This is accomplished as the second blower adds its pressure
capability to the
system, increasing the capacity beyond the capabilities of the first
blower.
Ideally, two identical blowers installed in series
would result in the same CFM at the outlet of
the second blower as the inlet of the first one,
and nearly twice the static pressure as that
rated for either blower alone. However, some
variation will result in both air flow and
combined pressure because of the tendency
of air to compress under pressure. A good
understanding of how atmospheric pressure
and absolute temperature affect density is
required. Both of these factors are involved in
the proper selection of blowers. Density is
directly proportional to atmospheric pressure
and is inversely proportional to absolute
temperature (degrees Rankine).
Caution is necessary in selecting blowers for
series installation. It is generally accepted that
most pre-engineered blowers are capable of
withstanding twice their catalog rated static
pressure. In other words, where two blowers
are installed in series the second blower
housing should withstand the higher pressure.
There is, however, a need for concern when
the combined pressure exceeds twice the
rated static pressure for one blower. In series
applications involving three or more blowers,
or in any system in which positive or negative
pressure exists prior to the consideration of
the blowers, special housing reinforcement
may be necessary.
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