Howden Roots RAS Whispair, Инструкция по установке, эксплуатации и обслуживанию

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ILRB-3000 GEA20261
RAS and RAS-J WHISPAIR Blowers
Page 17 of 33
Rotary Lobe Blower Vibrations
Blower vibration levels should be monitored on a regular basis. Take measurements at the bearing locations on the housings
and refer to the chart below for guidelines on assessing the vibration severity of a rotary lobe blower rigidly mounted on a stiff
foundation. When vibration measurements indicate that a review is required, the installation should be fully evaluated to
determine and resolve the causes of vibration.
In addition, vibration level trends should be observed for progressive or sudden changes. If a change occurs, the cause should
be determined through spectral analysis.
Blower vibrations are transmitted into the motor, speed reducer, and other system components. Make sure to obtain the
allowable vibration levels of all accessories from the associated vendors.
Note: Rotary lobe blower vibrations are measured in inches per second. The measurement of spike energy is not recommended
for judging blower condition because the rotary lobe blower has inherent impacting bearing loads.
The following items generate vibrations in rotary lobe blowers:
• Inherent rotary lobe blower characteristics can lead to vibrations:
− Impacting bearing loads excite component/ system natural frequencies.
− Pressure pulsations set off vibrations at four times the running speed (RPM).
• Very close clearances between the impellers and the housing can result in vibrations set off by impeller contact:
− Impeller to impeller frontal lobe contact. If contact is between only one set of lobes, the vibration frequency is one times the
RPM. If both sets of lobes contact, the vibration frequency is two times the RPM.
− Impeller to cylinder contact. The vibration frequency depends on the number of impeller tips contacting the cylinder and can
range from one to four times the RPM.
− Impeller to head plate contact. The vibration frequency is erratic and unsteady.
• Damaged gears generate vibrations at mesh frequency (number of teeth times RPM).
• Damaged bearings generate vibrations at ball pass frequency, fundamental train frequency, and ball spin frequency.
• Rotor unbalance and a bent shaft generate vibrations at one times RPM.
• Blower/driver coupling misalignment generates vibrations at one times RPM and two times RPM.
• Acoustic resonance in the blower inlet/discharge piping generates vibrations at four times RPM.
• Operation of a rotary lobe blower at or near system torsionals may cause impeller lobe contact and increase vibrations.
• If external piping is not properly isolated it will transmit vibrations into the blower.
• The foundation design and mounting method considerably affect blower vibrations.
Maintenance/Replacement
A consistent program of inspection and maintenance is the most reliable way to reduce the need for costly blower repairs. To
help establish a regular maintenance schedule, keep a simple record of procedures and dates. While operating the unit within
its specified rating limits is the best way to help ensure a satisfactory service life, the following basic ongoing service needs
should also be performed:
• Lubrication
• Cleaning
• Checking for hot spots
• Checking for increases or changes in vibration
• Frequently observing inlet and discharge pressures to ensure that blower ratings are not exceeded In a properly installed and
operated blower, there is no moving contact between the two impellers, or between the impellers and cylinder or headplates.
Wear is confined to the timing gears, the bearings that support and locate the shafts, and the shaft oil seals. When properly
lubricated with clean oil of the correct grade, only normal wear should occur. Shaft seals (lip type or rotating mechanical type),
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