Advantages of Rotary Positive Displacement Blowers Versus Centrifugal Blowers

Centrifugal blowers are generally more expensive than positive displacement blowers.
Centrifugal blowers operate at high speeds (up to 30,000 RPM) and, as such, rely heavily on
instrumentation which monitor many conditions to protect against unfavorable operating
conditions.

If such instrumentation fails, or is not utilized, a centrifugal blower will often fail to the point that
replacement is the only repair alternative.

A positive displacement blower will provide definite warnings prior to failure allowing the user
to remove the unit from service prior to the occurrence of major damage.

Also Read: Blower Bearing Life

Positive displacement blowers deliver a generally fixed volume with varying inlet and/or
discharge pressures. The throughput of a centrifugal blower can vary significantly with only
minor changes in inlet or discharge pressure.

In most cases, usually 250 HP (185 kW) and below, positive displacement blowers operate
more efficiently than centrifugal blowers. Always compare power consumption vs. delivered
volume at operating and off operating points.

The internals of a centrifugal blower must be kept scrupulously clean at all times. By contrast, a
positive displacement blower is less sensitive to fine material passing through the machine.
Centrifugal blowers do not operate well in high vacuum applications (<0.5 ATM) and cannot be
used as vacuum boosters.

Similarly, centrifugal blowers do not operate with good repeatability of process when handling
low density gases such as helium.

Positive displacement blowers are available with gas-tight mechanical seals, generally avoiding
the need for seal purge gas. Centrifugal blowers, due to their inherently high rotative speeds,
cannot utilize mechanical seals, and seal areas of units handling gas must be purged resulting
in more maintenance costs.

Centrifugal blowers cannot tolerate liquid presence in the gas stream and as such, are never
deliberately liquid injected. Positive displacement blowers can be specifically designed for liquid
injection to increase performance and/or volumetric efficiency.

Positive displacement blowers can generally be repaired or overhauled in the field by
competent mechanics with basic tools. Repair or overhaul of centrifugal blowers generally
requires sophisticated equipment and specialized technicians.

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