When contractors are installing mechanical equipment and there is a concern the vibration will get into the structure and cause unwanted noise, the "go to" solution is often the humble rubber pad. Pads can come in different durometers (hardness), sizes, and thicknesses. They can be solid or it can be formed in a waffle pattern. There are a variety of options, but how do you pick the right one? Here are 5 tips on how to get the best vibration isolation to ensure that you won't have a noise issue once the equipment is commissioned.
Be Aware of the Limitations - With vibration isolation, increasing the static deflection of the isolators (squash under load) will give you better vibration isolation. Compared to rubber mounts or springs, pads do not have a lot of static deflection. If the equipment you are mounting has an RPM below 1200, a high horsepower motor, or it is close to a sensitive area, you will want to contact your vibration isolation supplier and have them recommend an isolator better suited to your needs.
Size Matters - Bigger is not always better. In fact it is often better to have a smaller pad, but the key is to match the size and capacity of the pad with the weight of the equipment, not the size of the mounting plate. When you buy your isolation pads from a trusted vendor, they will be able to tell you exactly what the loading should be and provide you with documentation to maximize the results. Typically you will want the load on the pad to be close to the capacity so the pad deflects under load. It is the deflection that is the most important aspect of any vibration isolator. Thicker pads will deflect more than thinner pads, and waffle pads will deflect more than solid pads. Choose wisely.
Proper Support - Once you have the perfect pad for your installation, you need to make sure it has a bearing surface large enough for the pad. If you leave the sides of the pad exposed you will not be loading the pad the way it was intended , which will likely overload it. The is particularly an issue with waffle pads since the support is generally around the perimeter. A good practice is to make sure the dimensions of your bearing plate is at least 1/2" greater than the pads.
Don't Keep it Tight - In seismic zones or any application where the equipment will be bolted down, you absolutely must use an isolation grommet on the bolt, and it should never be torqued down on the pad. Use a double nut on the bolts, hand tighten the first nut, back it off a turn, and then lock it into place with the second nut. The double nut is important because the pads allow the equipment to vibrate and a single nut will loosen over time.
Do Keep it Concentric - Sometimes it isn't easy to get that anchor bolt hole drilled in the exact right location or to keep it perfectly plumb, but if there is any pressure on the grommet, vibrations will bypass all your hard work. When the installation is complete there shouldn't be any binding and the grommet should be able to spin freely.
