Fuel Gas Screw Compressor with axial high vibration
Fuel Gas Screw Compressor with axial high vibration
(OP)
Hi all,
I have a screw compressor, which is fuel gas compressor. It has 4 female/6male screws no timing gear. The customer want to reduce vibration because they had to welding cracked pipe and structure caused by high vibration.
The highest vibration freq. is 4x rpm, it could be screw mesh freq. I guess. And, the direction is axial.
Hor. and ver. vibratin is about 4mm/sec but axial is 17mm/sec. Not to mention, dominant freq. is 4x rpm.
I also checked the structure vibration, exactly this 4x rpm is main vibration on the structure and pipe.
I need your help for reducing this vibration.
If you have any information and experience, Please tell me about anything.
I have a screw compressor, which is fuel gas compressor. It has 4 female/6male screws no timing gear. The customer want to reduce vibration because they had to welding cracked pipe and structure caused by high vibration.
The highest vibration freq. is 4x rpm, it could be screw mesh freq. I guess. And, the direction is axial.
Hor. and ver. vibratin is about 4mm/sec but axial is 17mm/sec. Not to mention, dominant freq. is 4x rpm.
I also checked the structure vibration, exactly this 4x rpm is main vibration on the structure and pipe.
I need your help for reducing this vibration.
If you have any information and experience, Please tell me about anything.





RE: Fuel Gas Screw Compressor with axial high vibration
The following is based on assumptions.
Asuming a rotational speed of 1800 RPM(?) the frequency is 4*1800/60 = 120 hz. This gives an acceleration about 1.2G and a displacement of about .05 mm (about .002"). That seems like a small displacement. Is the dischage pipe exactly matched up to the compressor so there is no strain on the compressor? Is there a resonance in the discharge pipe? Can the discharge pipe move freely in reponse to temperature changes and vibration levels? How was the cause of the pipe failure determined? Is the compressor on isolation mounts?
Regards
Dave
RE: Fuel Gas Screw Compressor with axial high vibration
I suspect that the high vibration would be main cause for pipe crack. I checked vibration data from several points, on both side of Compressor and some points of pipe lines. Whole machine including structure is rattling. The source of that is 4x rpm(14325cpm). The running speed of Compressor is 3550 rpm.
Highest vibration is 5.411 G, Peak to peak on that freq.
It is equal to 23.588 um(PtP), 0.929 mils.
Autally, We had to fix the crack of some pipe lines and structure frames until now.
I also suspect the resonance in the pipe.
But, I would like to reduce the source of vibration. That is best way to avoid the resonance.
RE: Fuel Gas Screw Compressor with axial high vibration
Mike Halloran
Pembroke Pines, FL, USA
RE: Fuel Gas Screw Compressor with axial high vibration
Mike, with this class of machine I have had pretty bad experience with bellows. The pulsation tore the metal bellows up and ended up filling the enclosure with gas. I try to avoid bellows on screw compressors.
RE: Fuel Gas Screw Compressor with axial high vibration
Is the vibration new? Without timing gears, I'd conjecture the rotors would scuff and otherwise misbehave as they approach end of life.
Mike Halloran
Pembroke Pines, FL, USA