Working on a two speed Marley cooling tower I measured vertical amplitudes on the motor of .2 ips @ 1785 cpm and 2.8 ips at 1195 cpm. Both were running speed. Axials were .19 ips at 1785 and 2.06 at 1198. Horizontals were.152 @ 1785 and .862 at 1198. Couldn't get phase data or do any bump tests.

This sounds like misalignment and a resonance in the mounting structure (see posting about natural frequency calculations), but there are also some questions about the couplings and floating shafts.

Any experience out there with the Marley couplings with with the rubber bushings and bolts. Shafts are about 8 feet long.

Thanks,

Danny

I have three Marleys at one site--brand new--with a natural frequency of 1820 rpm. I bumped the motor, base plate and the 'torque tube' (that links the motor base and gearbox base) and everywhere was 1820. Makes it real tough to run them wide open. One of the design guys from Marley came out with some field service guys. They checked the alignment and everything was within 0.005" TIR which is their spec. We ended up putting a tuning fork on them to absorb the vibration.

Patrick,

I'm pretty sure that a pretty simple stiffening of the motor bases and correcting the alignment or whatever other problems with the torque tube or couplings will get things down to a dull roar here. Fortunately, it works fine in high speed, so for now while it is hot it can just run there.

Thanks,

Danny

If the torque tube has been replaced recently, be advised that I have seen more than one Marley shaft with runout/balance issues new from the OEM......

Danny,

Usually the high vertical and axial indicate a rocking mode resonance. I have often found that a good alignment and precision in-place balance of the coupling half on the drive-end of the torque tube usually takes care of the problem. I have also installed dynamic absorbers in the eyebolt hole on top of the motor. Good Luck, John

Try a dial indicator on the jackshaft too. It could be going thru a bending mode.

To further exemplify the above posts, one of my customers called me today about a brand new cooling tower they were commissioning. He said it had a little shimmy (not as bad as a shake). I measured motor horizontals about 0.4 ips, motor axial about 0.5 ips and three points on the gearbox at about 0.4 ips--all at 1X motor. With the high axial you'd think misalignment but it was within 0.003" on both ends. The next thing we looked at was the jack shaft. It had a runout of 0.060" in the middle (about a 12' shaft). Come to find out, it sat onsite for about 6 months during construction, apparently not being rotated or supported or anything. The OEM is sending a new shaft.