How to Select Anti-Vibration Mounts for Machinery

What anti-vibration mounts do

Anti-vibration mounts, also called vibration isolators or AV mounts, sit between a machine and the surface it stands on. They absorb the vibration a running machine produces, so less of it passes into the floor, the structure and nearby equipment. That protects the building from shaking and noise, protects the machine from shock, and keeps vibration from disturbing sensitive equipment close by.

How they work

A machine vibrates because its moving parts are never perfectly balanced. An anti-vibration mount places a flexible rubber element, bonded to metal fixings, between the machine and its base. That element flexes under the vibration and absorbs the energy instead of passing it through to the floor.

The weight of the load and the hardness of the rubber have to be considered together when selecting a mount. Neither means anything on its own. Rubber that works well under a heavy engine will be far too stiff under a light one, and the mount will barely isolate anything.

What varies between mounts

Machine mounts are built around the same idea, but they differ in how much movement they allow and in how the machine is held:

• Standard machine mounts are the everyday choice. They isolate vibration, take up a little misalignment and are simple to fit. They suit engines and generating sets.
• High-deflection mounts allow more movement under load. The extra deflection isolates the slow, heavy vibration that a stiffer mount passes through.
• Fail-safe mounts include a captive fixing that keeps the machine located on its base. They are used where the machine must not shift, such as on a vessel or a raised structure.

AVM supplies GMT rubber mounts, including the Triflex machine-foot range, high-deflection mounts and fail-safe types.

How to choose the right one

Four things decide the mount, and they are worked out together rather than one at a time:

• The load on each mounting point. Weight is rarely shared evenly, so work out what each mount carries, not just the total weight of the machine.
• The rubber hardness that suits that load. Load and hardness are chosen as a pair, and the mount is matched to the weight it actually takes.
• The force to be damped, and its direction. Running speed alone is not enough. Speed together with weight gives the force the mount has to absorb, and that force acts in particular directions. A mount that handles it vertically may not handle it sideways, which matters on a vessel that rolls and pitches.
• The environment. Salt water, oil, heat and UV all attack rubber, so the compound and the finish are chosen to suit the setting.

Sizing a mount on weight alone, or on running speed alone, is the usual reason an installation still shakes after the mounts are fitted.

Where anti-vibration mounts are used

Anti-vibration mounts are fitted under engines and generating sets, and on the machinery around them: pumps and compressors, fans and exhaust systems, gearboxes and shaft lines. They are used anywhere a machine would otherwise shake its base, pass noise into a structure, or disturb sensitive equipment nearby. On vessels they have to keep working while the hull itself is moving.

To see the anti-vibration products AVM supplies, visit the anti-vibration category.

Frequently asked questions

What are anti-vibration mounts for?

They sit between a machine and its base to absorb vibration, so less noise and shaking pass into the floor, the structure and nearby equipment. The mount is matched to the weight it carries and to the rubber hardness that suits that weight.

How do I choose the right anti-vibration mount?

Work out the load on each mounting point, pick the rubber hardness that suits that load, then check the force the machine produces and the directions it acts in. Finally match the rubber to the environment.

Why does the load on each mount matter so much?

A mount only isolates well when the load it carries and the hardness of its rubber are matched. Too stiff for the weight and it barely works.

Why is running speed alone not enough?

Speed tells you how often the force is applied, not how big it is. The weight has to be added to work out how much force the mount absorbs, and in which directions.

What is a high-deflection mount?

A mount that allows more movement under load. The extra deflection isolates slow, heavy vibration that a stiffer mount would pass straight through.

Do anti-vibration mounts work on a vessel?

Yes, and the choice is stricter there. The mount has to cope with the machine's vibration and the movement of the vessel, and the rubber has to resist salt water, oil and temperature swings.