11/23/2022

Choosing a simple Anti-Vibration Mount? Part 3: Load

 Written by Daniel Lawes

This is normally an easy step.  Once we understand the static deflection requirements, we need to look at the load we are trying to isolate on each mounting point (or foot).

Key questions:

To understand the load per mount, we need to understand:

1. How heavy is the equipment we are isolating?
   • Use the max load incl. any fuels, pipework etc that can increase the supported weight.  We have seen overloaded mounts due to the shipped or dry weight being used.
2. How many feet does it have?
3. Is the centre of gravity evenly positioned over the feet (so, is the load evenly distributed)? If not, we need to take some moments to calculate the loads per foot.  This is not tricky, but I will cover it separately.  For now, let’s assume loads are evenly distributed as they are for most of our day-to-day enquiries.

From this, we can work out how much load is on each foot or mount.

Why does load matter?

Well, there are a few reasons:

1. Mounts have a working range.
   • If you overload a rubber mount the worst-case scenario is tearing, failure and/or collapse. At a minimum the mount will be less effective at its job as when an AV mount is over compressed it ‘bottoms out’ and becomes solid, which prevents it from isolating.
   • If your mount is insufficiently loaded it won’t do its job either – it might not deflect enough resulting in reduced isolation and potentially resonance.
2. We want all the mounts to have a similar level of deflection to avoid an imbalance in the natural frequency of the system we are generating. We will talk more about this in another post.

So, we need to know that the load will sit in the AV mount’s “goldilocks zone”:

1. Not too much load to avoid overloading
2. Not too little load to work the mount properly and to avoid the risk of resonance.

For simplicity, assume our pump from the example in “Part 2: Static Deflection” weighs 1,000 kgs, and that weight is supported evenly by 4 feet, so 250kg/foot.

Relevant Links:

For other parts of of this lesson, click here:

1. Introduction to this lesson
2. Basic Principles of Vibration Management
3. Static Deflection
4. Mount Selection