Noise control for lab sized high vacuum pumps

Hi Russell,

I can't speak definitively without seeing the installation, but, the easiest solution would likely be active noise cancellation. If you rely only on architecture to solve the problem you may have other issues of space, construction, heat dissipation, etc.

If this is of interest to you, you can search for 'active noise cancellation' solutions via Google or others, or if you like, maybe I can find some solutions.

Regards,

Hi,

Your best bet is to make your own enclosure and line it with sound insulating foam. The easiest way to make the enclosure is from modular extuded aliminum. http://www.item.info/en

If you give this company the measurements they will send you the flat pack kit within a week or two. You will probably have to line the box with foam yourself. (if you ring them they may have already have a solution as they design specifically for machine enclosures)

The company also supply a free Autocad add-on which will help you design it yourself from a list of standard companents and report a Bill of materials which you send to "ITEM" for quotation.

Please note "ITEM" are not the only company specializing in this field. Have a Google if there are no ITEM distributors within reasonable shipping distance.

Regards

J.

Russ, is it the noise that is objectionable, or is it the transmitted vibrations, or a combination of both?

Setting the pumps on isolation mounts would solve the transmitted vibration problem, and sound insulating blankets or a sound enclosure would work for the rest. You should be able to goggle sound enclosures for pumps and find something...

Your ME department should have a vibration guy that could design the isolation mounts, but google isolation mounts and you will find plenty of options as well.

What kind of vacuum pumps are you using? Nash liquid ring pumps should not be very noisey...

Hi,

I am operating several high vacuum systems: pre-pumps, no roots-blowers, turbo-molecular pumps.

Pre-pumps are vibrationally decoupled by flexible connections, noise is tolerated or pumps are relocated into next rooms.

Turbo-pumps are very sensitive to vibrations: avoid these to a much lower level than in any other equipment (except ultra-precision machining and inertial quality gyros).

(Or select turbo-pumps with magnetic-bearings.)

The sensitivity of turbo-pumps with ball-bearings is a result of the high angular momentum (from rotor z-inertia and high speed) and the cross-coupling of radial into angular vibrations (by mass- and stiffness distribution).

Depending on the flexible construction that supports the outer rings of the ball-bearings this is generating radial loads on the bearings (frequency dependent).

This should be avoided as far as possible: any vibration above the level that can be feeled by fingertips is to be considered as shortening the useful life.

As any ball-bearing units are generating disturbing noise there is only one simple remedy: make a second housing around the turbo-pump ( a distance of 1 mm is ok but 10mm is convenient) that is totally flexibly decoupled from the pump and use this second housing as a conduct for cooling air if air-cooled.

If vibration level has to be much more down (electron microscopes and tunnelling microscopes) then a flexible (very flexible) metallic connection between pump and vessel will be necessary.

Have success

RHABE

The previous comments about isolation mounts & flexible bellows in the connecting pipes are the first steps. We have built our own housings out of MDF sheet lined with acoustic foam but you have to consider how this affects the running temperature of the pump.

I have the same problem- loud vacuum pumps in the immediate vicinity of work stations. There are two complicating factors that make soundproofing difficult. 1; the motors are air-cooled, which prevents the use of a simple soundproof enclosure. 2; the longer the connecting tubing that goes from the pump to the device being evacuated, the less efficient the pump becomes. This can prevent removing the vacuum pump to an adjacent room. I would like to know how active noise cancellation may be used in this situation (much of the noise is high frequencies).

Bill Morrow

Active noise cancellation is very effective, but application specific. For mid to high frequencies it gets a little complicated because one has to identify what is radiating the energy, and in what directions in order to properly place transducers. As I said earlier, there's not a lot that can be done without knowing the exact installation.

If it were my dilemma, I would begin empirically with the equipment as installed measuring the noise spectrum in various locations away from the equipment, and on the equipment. If the propagation is coming from singular sources on the equipment it is easier to find a way to damp those fields.

I know I've talked too much without offering any concrete solutions, but it is difficult without being able to know more and analyze more. Sorry.

Still, active noise cancellation is a bona fide way (not the only way or always the best) to tackle some problems.

http://www.chrisruckman.com/ancfaq.htm

This site may give you some answers.

If you want to 'plow' further with this, let me know and maybe I can help.

(please don't misinterpret this as a solicitation ... I'll help all I can with 'suggestions', but tangibly there is not much I can do other than 'point you' in this direction or that.)

Take care ...

Hi,

we directly attach the pump to the chamber (if inlet diameter is 100 mm then there is a 100mm long tube with some ports for pressure measurements and may be a protective grid).

If air-cooled its easy (and necessary) to switch to water cooled: press some turns of copper tubing near the motor to the housing with a bandage and make sure there is good thermal contact by using heat conducting paste (from power semiconductors) or SiC filled epoxi. We use mesh 800 SiC, the mixture is very very high in viscosity but still a Newtonian fluid!

RHABE