Vibration Problem Coming from the ceiling

[emrecan88]

Dear All,

I have a vacuum chamber set up in my lab sitting on the vibration isolation table. There are gas lines coming from the ceiling and connected to the chamber. Stainless steel 1/4" gas lines are clamped to the ceiling, but that connection conducts the vibration from the ceiling to my experiment. Is there any good isolation clamp idea for this case (to connect my flow line to the ceiling isolated)?

Appreciate for your help in advance

 

[MikeHalloran]

Get some much longer gas lines, and coil them in a big helix, like a coil spring.



Mike Halloran
Pembroke Pines, FL, USA

 

[KENAT]

Or clamping the line between some foam (or similar) which is attached to something heavy/stationary remote from the table top can help too.

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[tygerdawg]

Do both.
Coiling extra length is a good start, but only adds a spring element to the system. You need damping to really control the induced force caused by vibrational input source.

Looks like a good Senior Vibrations project.

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering

http://www.bluetechnik.com

 

[KENAT]

Or the kind of thing we face around here all the time.

(So if someone comes up with a really good approach I'll be poaching it too;-))

Think about how you're going to suspend/restraind the 'coil' - using a component with some damping - perhaps from hysteresis - may be an idea.

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[dvd]

I'd lean toward a short length of braided stainless steel hose connecting the chamber to a (possibly larger) header. What gas/pressure is being transmitted in the piping? Also, possibly investigate whether resonance is an issue.

 

[KENAT]

Doh, I suggested a vacuum accumulator for a vaguely similar problem just a few weeks back, can't believe I forgot to mention it.

You could do it in line, or depending how long you need your experiments to run/what pressure differential/what volume etc. you could just run off an accumulator for the duration of the experiment.

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[KENAT]

Rereading your OP you could try putting some damping material between the pipe hangars and the ceiling (maybe sorbothane or something) but I'm skeptical how well you'll be able isolate the vibration this way.

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[Tmoose]

When isolation is the goal, Unless resonance is involved (the forcing function frequency is near the resonant frequency of the isolated system) damping will only increase the transmitted force.

http://www.gallaghercorp.com/i/pb-12-a.jpg

Also note that at the 1.2 ratio the transmitted vibration is about the same as if rigidly mounted, regardless of amount of damping

 

[hacksaw]

from operating plant to high tech manf. straight tubing conducts plenty of vibration,

advice is that no straight runs to the protected equipment, you need a bend or two,u-bends are most common, or a simple loop, followed by a piece of pressure/vacuum rated flex hose to your equipment.


most tables include damping, mass and otherwise, so you may need to tie the tubing to the table after the isolation bend but before the flex connection

 

[MikeHalloran]

Some gases you don't want to put through a flex hose, because they won't stay in it, and you don't want them out.

Coiling a rigid tube into a helix many times its own diameter effectively turns it into a coil spring with a super low rate, hence very low transmissibility.



Mike Halloran
Pembroke Pines, FL, USA

 

[hydtools]

I was going to suggest bungie cord suspension, but maybe this would more 'industrial':

http://www.kineticsnoise.com/hvac/shaashab.html

Ted

 

[GearsNsparks]

Search for spring hangers/vibration isolators/vibi.

Common sources are:
Kinetics Noise Control
Mason Industries
CalDyn

Determine what ranges of frequencies you are trying to mitigate, that will control the static deflection used for sizing the appropriate isolators. A good starting point would be to use the same static deflection criteria as for the equipment mounting, and adjust for the effective mass of the pipe being supported per hanger.

 

[GregLocock]

In addition to the coil idea, which is the nice way to do it. consider clamping a very large mass (5-20 kg) to the pipes. You'd be surprised how many vibration problems on cars used to be troubleshooted and sometimes solved by this rather inelegant method.

A bag of cement is also handy.

Cheers

Greg Locock


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[KENAT]

What material or type of tube is actually connecting your chamber to the 1/4" ceiling gas lines?

I was thinking PU tubing or similar as we typically use which is why I asked about how you were restraining the coil etc. However, rereading your op I'm not so sure.

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[GregLocock]

I read 1/4" SS.

Is the material they are made of important? There is a flexible copper brake tube available for cars that you can bend by hand to make the spiral from - getting SS tube bent up professionally can be expensive.

Cheers

Greg Locock


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[KENAT]

Well, the type of plastic tubing (arguably hose as it's flexible) we use doesn't easily hold a 'spiral' although you can buy preformed helical lengths - at least the 1/8 OD stuff.

Initially I was thinking the main supply pipes were the stainless, but now I realize it seems the run from the ceiling to the chamber may be the SST.

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[emrecan88]

Dear All,

First of all thank you very much for your helpful suggestions. I try to answer your questions. I also attached the images that show how the lines are connected to the table and how the tubing connected to the ceiling.
At my side we are now giving the order for flexible hoses to put between the table and rigid tubing.
- Coil spring idea has been thought, we can try that. But once we put the flexible hoses, I don't think it will improve much.
- There is 5-30 psi pressure in the line.
- I didn't get the idea about vacuum accumulator usage though.
- I agree for high frequency case damping might not be helpful at all, but we are not sure about our noise frequency.
- For the material of the tubing, we are running experiments in the condition which should be very clean. Impermeability is our necessity and that leads to an only choice Stainless Steel material for connections. Otherwise I have seen this problem was overcome by putting plastic flow lines.

Thanks a lot again for your kind suggestions

Emrecan Soylemez

 

[KENAT]

On the vacuum accumulator, idea is that you'd connect the chamber to the accumulator, and the accumulator to central vacuum.

Given you're stuck with rigid pipes my comments about 'in line' operation are out. However, you could imagine disconnecting the accumulator from central vacuum while running experiments. This would isolate your chamber from the central vacuum.

(Funnily enough I saw one of our discontinued high vacuum instruments down stairs fresh from refurbishment and noticed that it has KF40 or similar connection on the back so probably ran from rigid lines not flex.)

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[Tmoose]

"we are not sure about our noise frequency."

I would not gamble much time or money until I had that info identified.

There is Not much reason not to gamble, since Every computer these days has a sound card capable of decent recording. There used to be several free spectrum analysis softwares on line.