Turbine vibration test, key method.
 

Has anyone heard of this test? Place your house key (without the key ring) on top of your turbine, if at full power the key falls off the turbine you need to have your bearings checked or your turbine is out of balance. What amount of vibration is considered OK?

I tried this test above on a JB-220 and the keys stayed in place.

I don't have a house key... I use a garage door opener, will that work ??

I have not heard of that, but I know with experience, you can feel the bearings going if you hold a screwdriver or a key in your hand and put it on the end of the turbine near the rear bearing. Hard to describe the feeling but it works, but you have to have a feel for a good motor first, obviously.

if the key gets sucked in, the engine need some maintenance for sure.... ;)

Always use fod screen for test.

I saw this test done with a heavy duty screw driver place on the case close to the cone or the compressor. Saw this at RAM.
The screw driver vibrate at the tip and won't stay still. then you hear "backward masking voice lol" just kidding about the backward masking voice part :)

So whats the deal then, should the screw driver stay in place without vibrating or some vibration is ok?

It should sit there without any vibration..almost like if the engine is not running.

Well if that is the case this jet central cheeta I have has failed :(

Not surprised, vibration is a product of combustion, not necessarily to do with rotating parts.

Just saying m

The easiest way to test vibration is to just use something like a 3/32 ball driver and when going through your throttle setting just put it on top of the turbine or top of one of the screws. Trust me if you have a vibration you will feel it.

Always be carful especially if you do feel any vibration also always stand in front of the turbine and not on the side or rear.

Ok first and foremost...what caused you to check for balancing in the first place. You could be mistaken vibration for something else. I would have someone that have more experience to check it out.

exactly, IMHO this test only works if you have experience probing with a NORMAL turbine with good bearings. The key is the difference. I would not know how to tell someone what to feel for. And I would not balance anything on the turbine, I can feel it fine by hand.

Well...doing process safety management and predictive maintenance on commercial turbines vibration analysis is common. Only thing is, the equipment is slightly more advanced...with software.

I've seen others use this technique as well, actually and it has basis, but maybe not merit. I do know people have identified bearings about to fail this way, but seems like you're really pushing maintenance limits, because if you can tell from vibrations you can feel, how close do you think you are to catastrophic failure? Wonder if portable vibration monitoring equipment has a place here? Keep tracking from known good readings and track vibration amplitudes...

You can hear a different pitch on the sound when the turbine is run at max rpms, after running your turbine for some time you will notice the difference of the sound.

I agree. I can tell by sound if the bearings are going bad or the turbine is out of balance.

A hand tool resting against the casing while running through idle thru full throttle settings should easily identify any excessive vibration. A good method of keeping track of the heath of your bearings is to pay attention to the cooling cycle; if the rotor assembly sounds noisy or the time it takes the rotor to come to a stop after starter disengagement changes significantly, you may want to have the engine checked for imbalance or worn bearings.

Dreamworks offers full in house turbine services, free turbine inspection and health checks for numerous brands of turbines including; Jetsmunt, Simjet, Ram, JetCentral, Wren and AMT. Our indoor turbine lab is equipped with a state of the art core balancing system and test cell.
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