Regarding fan vibration issues
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I have two fans here, with a rated speed of 980 rpm. One is used to handle air at a volume of 480,000 standard cubic feet, while the other is used to handle the flue gases resulting from natural gas combustion, at a volume of 680,000 standard cubic feet. After operating for about 16 months, it has always been the case that once the fan speed reached around 780 revolutions per minute, the horizontal vibration on the non-driving side increased sharply; an increase of 3 to 5 revolutions was sufficient for the horizontal vibration to rise from 4.2 mm/s to 4.6 mm/s. Other vibrations are normal. The air inlet is equipped with a self-cleaning filter, and alignment is also no problem.
It must have a lot to do with the foundation of the unit
Check if there are any issues with the base bolts; look for the cause in the installation process
First, the unit foundation needs to be considered, and secondly, the fan bearings.
The horizontal vibration at the non-drive end increased from 4.2 mm/s to 4.6 mm/s; this is likely due to a large coaxiality error between the motor and the input end of the bearing housing. The value of 4.2 mm/s is on the high side – it should be below 3.5 mm/s under normal conditions； Also, check whether the base shims meet the specifications.
This post was last edited by Zaza Ya on 2015-12-3 at 18:08. This is likely a problem related to the dynamic and static balance of the machine. Before leaving the factory, the fan’s casing and impeller must undergo dynamic balance testing. According to what you said, your body’s grade should be G2.5, and it has now exceeded that level. You can negotiate with the supplier to perform rebalancing (it’s quite troublesome to do rebalancing after the fan has left the factory), as long as the fan does not exhibit such vibration issues after leaving the factory. Technical support can be provided to the original poster if needed.
This post was last edited by Zaza Ya on 2015-12-3 at 18:08 QQ 1xxxxx
Such a small increase can be ignored. If both machines have this issue, consider the possibility of structural resonance and check whether there are any loose parts in the foundation; if not, reinforce it horizontally to increase its natural frequency.
From what the poster says, it seems there’s resonance; you can try increasing the speed to get past that speed range and see what happens. For extra safety, check the installation of the bearing housings on the non-driving side, reinforce the foundation, and then observe the vibration levels when the speed is increased to 780. If there is an improvement, it indicates resonance. Under normal conditions, the effective value of the vibration speed for equipment operating at over 900 revolutions per minute should be below 3 mm/S; 4.5 is too high. Collect the data from various measurement points on the fan to see if there is any issue.