HVAC vibration isolation and equipment mounting field guide

Vibration isolation, and why the structure is what you protect

Vibration isolation separates rotating or reciprocating HVAC equipment from the structure it sits on, so the shaking the machine makes stays in the machine and does not travel into the building. Fans, pumps, chillers, air handlers, and compressors all have parts that spin or stroke, and none of them run perfectly balanced. The leftover imbalance becomes a force that pushes on the equipment feet at the speed the machine turns. Bolt the feet straight to a concrete deck and that force goes into the deck, then into the columns and the slab above, and comes out as a rumble in the space below or two floors over.

The isolator is the soft layer in between. A spring, a rubber mount, an air bag, sized so the equipment can ride on it and the force has somewhere to go besides the structure. The job is narrow and the physics is old, but the field execution is where it lives or dies. An isolator that is shorted out by a rigid pipe, a forgotten shipping bolt, or a chunk of grout under the base does nothing at all, and the equipment might as well be hard-mounted.

This guide covers the theory you need to pick the right mount, the isolator types, the bases under them, and the connections that have to stay flexible for any of it to work. The air handler and the pump each get their own treatment in their own guides. Here the focus is the mounting and isolation that ties any of that equipment to the building.

What you are actually preventing

Three things drive the decision to isolate, and they do not weigh the same on every job.

The first is noise in the occupied space. Vibration that reaches the structure radiates back out as low-frequency sound, the rumble and drone an occupant feels as much as hears. It travels far through concrete and steel and shows up in a conference room or a patient room nowhere near the mechanical room. This is the complaint that gets the contractor called back, because it is hard to chase after the building is closed up and the equipment is already bolted down.

The second is the equipment and its connections. A machine that transmits its vibration into rigid pipe, conduit, and duct is also feeding that vibration back into its own joints and the building's. Pipe connections fatigue and weep, flex points crack, and the equipment's own bearings and seals wear faster when the whole assembly is shaking against a hard mount.

The third is the contract and the code. Many specs call out an isolation scheme by equipment type and floor, and a mechanical room over an occupied space often carries a structure-borne noise limit the design has to meet. On the comfort side, a tenant who feels the chiller through the floor is a tenant who calls the property manager. Isolation is cheaper to design in than to retrofit, every time.

How does vibration isolation actually work?

Isolation works by tuning the mount so its natural frequency sits well below the frequency of the force the equipment makes. Every spring-and-mass system has a natural frequency, the rate it wants to bounce at when you push it and let go. The equipment makes a disturbing frequency, set mainly by its running speed: a fan at 1,200 rpm pushes at 20 cycles per second, its rotating speed. When the disturbing frequency is far above the mount's natural frequency, the force tries to push the equipment faster than the soft mount can follow, so most of it gets absorbed in the mount instead of passing through to the floor.

The ratio is what matters. A common rule of thumb is that you want the disturbing frequency at least three times the natural frequency of the isolator to get meaningful isolation, and many references tie roughly 90 percent isolation to a natural frequency near one-third of the disturbing frequency or lower. The further apart they are, the better the isolation.

The trap is resonance. If the mount's natural frequency lands near the disturbing frequency, the system amplifies the vibration instead of cutting it, and you have made the problem worse than a hard mount. This is the danger with low-speed equipment and with variable-speed drives that sweep through a range of speeds on start and stop. A soft enough isolator keeps the natural frequency well below the slowest running speed, so the equipment passes through resonance quickly on startup and runs well clear of it. Confirm the selection against the equipment's actual operating speed, and on drive-controlled equipment, the lowest speed it will hold.

What is isolator static deflection?

Static deflection is how far the isolator compresses under the weight of the equipment, and it is the number that sets the isolation. A mount that deflects 1 in under load has a lower natural frequency than one that deflects 1/4 in, and the lower the natural frequency, the better the isolation for a given equipment speed. That single relationship is why selection tables are written around deflection: pick the deflection and you have picked the natural frequency.

More deflection is better isolation, within reason. A neoprene pad might give you a fraction of an inch. A free-standing spring can give you 1 in, 2 in, or more. Slow equipment needs more deflection than fast equipment to clear the same isolation target, because its disturbing frequency is lower and the natural frequency has to drop further to stay well below it. That is the core of why a high-speed inline fan can ride on rubber while a low-speed reciprocating compressor wants tall springs.

The deflection that matters is the deflection in service, with the equipment at operating weight and the springs free to move. A spring rated for 2 in that is only seeing 1/2 in because the equipment is lighter than assumed, or because the base is also resting on something rigid, is not giving you the isolation the table promised. Hedge the exact figures to the manufacturer's selection and the project's specified deflection by equipment and floor. The deflection-drives-isolation rule holds, but the specific number is theirs to set.

Neoprene pads and mounts

Neoprene pads and molded rubber mounts are the basic isolator, for lighter and higher-speed equipment where you do not need much deflection. A ribbed or waffle pad under the feet of a small pump, a cabinet fan, or a packaged unit gives a fraction of an inch of deflection and takes the edge off the high-frequency vibration and the structure-borne hum. Molded neoprene mounts add a bolt hole and a steel top plate so you can fasten the equipment and still keep the rubber in the load path.

Rubber works well at high frequency and runs out of room at low frequency. It cannot give you the 1 in or 2 in of deflection a slow machine needs, so on heavy low-speed equipment a pad alone is not enough. Where you see it: small inline and cabinet fans, small circulators, condensing units, transformers, and as a second stage under spring isolators or under an inertia base.

Neoprene also ages. It takes a set under sustained load, hardens with heat and ozone over the years, and loses some of its give, so the oldest pads on a roof are doing less than the day they went in. Pick the durometer for the load so the pad sits in its working range, not crushed flat and not barely loaded. A pad squashed solid has no deflection left and is just a spacer.

Spring isolators

Steel spring isolators are the workhorse for larger and lower-speed equipment that needs real deflection. A coil spring can give you 1 in, 2 in, or more, which drops the natural frequency far enough to isolate slow machines that rubber cannot touch. Free-standing open springs sit between a top plate on the equipment and a base plate on the floor, usually with a neoprene cup or pad under the base so the steel does not couple high-frequency vibration straight through. A bare steel spring passes high frequencies well, which is the opposite of what you want, so the rubber under it covers that gap.

Springs come open or housed. Open springs are easy to see and to check: you can read the free height, confirm the spring is not coiled solid, and see daylight around the coil. Housed or enclosed mounts hide the spring in a can, which protects it but makes it harder to confirm it is actually working and not bottomed. Either way the operating point should leave the coil with travel left, so a load swing or a startup surge does not slam it shut.

The detail crews miss is that the spring has to be free to move. Painted in, grout-bridged, or bolted down so tight the spring is fully compressed, and it is not isolating anything. The spring earns its keep only while it can bounce.

Restrained and seismic springs

Restrained spring isolators are spring mounts with a built-in housing that limits how far the equipment can move, for seismic and high-wind locations and for equipment with a big weight swing. The housing has snubbing built in: under normal running the spring works as a spring, and only when a shock or a quake tries to throw the equipment past its limit does the restraint catch it. The goal is to hold the isolation during operation while keeping the equipment captive when it counts.

You need restraint where the equipment cannot be allowed to walk or topple: rooftop units exposed to wind, equipment in seismic zones, and machines like cooling towers and large fans that have a large operating-to-empty weight change or a big startup thrust. A free spring left unrestrained in a quake lets the equipment jump off its mounts, tear its connections, and become a hazard.

Restrained springs and separate seismic snubbers do the same family of job, and the principle is the same one repeated across the seismic restraint topic: the restraint has to engage only in the event, not drag on the spring during normal running. If the housing is adjusted so it is touching the equipment while it runs, you have shorted the isolator through the restraint. Set the gaps per the manufacturer so the spring is free in normal operation and the restraint is there only for the shock.

Air springs

Air springs, or pneumatic isolators, are for the very low frequencies where even tall steel springs run short. An air bag can be tuned to a natural frequency below what a practical coil spring reaches, so it isolates the slowest and most sensitive equipment and protects the most vibration-sensitive spaces. They usually come as a base frame with several air mounts, height-control valves, and a small air supply that holds the equipment at a set level as the load changes.

You do not see them on routine jobs. They show up under sensitive equipment, in critical spaces, and where the spec calls for a natural frequency a steel spring cannot hit. They cost more and they need an air supply and leveling valves that have to be maintained, so they are specified where the isolation target actually demands them, not as a default. Treat the selection as the manufacturer's and the acoustician's call.

What is an inertia base?

An inertia base is a concrete-filled steel frame the equipment is mounted to, sitting on the isolators, so the springs carry the machine plus a block of mass. The added weight does several things. It lowers the center of gravity and steadies the assembly, so the equipment rocks and moves less under its operating forces and its startup torque. It gives the isolators a heavier, more stable mass to work against, which improves the isolation and keeps a pump or fan from walking on its springs. And it soaks up the reaction from the equipment instead of letting the machine shake itself loose.

A common rule for sizing the mass is that the inertia base plus fill weighs on the order of one and a half to two and a half times the weight of the equipment it carries, with the manufacturer and the design setting the actual figure for the machine and its forces. Pumps are the classic case: a base-mounted end-suction or split-case pump on an inertia base with springs under it and flexible connectors at the suction and discharge is the standard mounting on a hydronic loop. Large fans with significant startup torque and unbalanced forces get them too.

Where a machine has a big single-direction thrust, like some fans, the base also resists that push so the equipment does not lurch on its mounts at startup. The base does not isolate by itself. It is mass the isolators carry, and the springs still do the isolating. The pump install guide covers the pump-specific base and connector detail; the point here is that the inertia base and the isolators are one assembly, designed together.

The housekeeping pad

A housekeeping pad is the raised concrete pad poured on the structural floor that the equipment, or the equipment's isolators, sits on. It is not an isolator. It is a mounting and a protector: it lifts the equipment and its connections above the floor so you can clean and drain around it, it gives anchors something solid to grab, and it raises the base out of any water on the deck.

Confusing the housekeeping pad with isolation is a basic error, and it shows up as equipment hard-mounted to a pad with no isolators at all, on the theory that the concrete will handle it. It will not. The pad transmits vibration to the structure as well as the bare slab does.

The isolators go on top of the housekeeping pad, and the pad has to be sized and anchored to take both the equipment load and the seismic anchorage. On an inertia base job you have a sequence: structural floor, housekeeping pad, isolators, inertia base, equipment. Keep them straight, because each layer does a different job, and the pad is the one that does no isolating. The AHU and pump install guides show the pad in the larger mounting sequence.

How do you select a vibration isolator?

Selection comes down to matching the isolator type and deflection to two things: the equipment, and where it sits in the building. The equipment side is its weight and its lowest operating speed. Heavy and slow wants more deflection and points you toward springs; light and fast can ride on neoprene. The location side is what is under the equipment and what is below that. Equipment on a slab on grade can use less deflection, because the ground under the slab is stiff and does not transmit much. The same equipment on an upper floor, especially over an occupied space, needs more deflection, because the floor structure flexes and carries vibration to the space below.

That floor rule is the one people miss when they reuse a grade-level detail upstairs. A unit that was fine bolted on light pads in a grade-level mechanical room becomes a rumble complaint when the same detail goes on the third floor over offices. The longer and more flexible the floor span beneath the equipment, the more isolator deflection it takes to clear it, which is why selection tables are organized by equipment type and by floor span or floor location.

The honest version is that the selection comes from the manufacturer's tables and the project's vibration isolation schedule, which list deflection by equipment and by floor. Use them. The principles here tell you whether a selection looks right, heavy-and-slow getting springs, upper-floor getting more deflection than grade, but the specific deflection by equipment and floor is the spec's call and the manufacturer's.

Why do you need flexible connectors on equipment?

Because a rigid pipe, duct, or conduit bolted to isolated equipment is a path that carries the vibration straight into the structure and shorts the isolators out. You can float the equipment on perfect springs and still feel it three floors away if a hard copper line ties the pump to the building. The vibration does not care that the feet are isolated; it takes the rigid path it has. Break every path or the isolation is for show.

At a pump, that means flexible pipe connectors at the suction and discharge, a braided or molded flex section that lets the equipment move on its springs without dragging the pipe along. At a fan or air handler, it means a flexible duct connection, a fabric break at the inlet and outlet so the fan's vibration does not pump straight into the sheet metal and out through the duct hangers. For power, it means a length of flexible conduit, a flex whip, into the equipment instead of rigid conduit landing hard on the housing. Even the condensate and the small gauge lines should not be rigid bridges.

This is the part the isolation drawing assumes and the field forgets. The springs get installed, then someone runs the gauge tubing or the conduit hard and tight from the equipment to the wall, and that one rigid line undoes the whole scheme. Every service that lands on isolated equipment gets a flexible break: pipe, duct, electrical, drain. Treat it as a rule, not a suggestion, because a single hard connection is enough to defeat the mounts.

Isolating the piping and duct near the equipment

The vibration does not stop at the equipment connection. It rides the pipe and the duct and can re-enter the structure through their supports and hangers downstream, so the piping and duct near isolated equipment get isolated too. The standard practice is resilient hangers, spring or combination spring-and-neoprene, on the pipe and duct for a run out from the equipment, commonly the first stretch from the connection, with references citing on the order of the first 50 ft or the first several hangers.

The reason is stiffness. A rigid clevis hanger is stiff enough to transmit vibration into the structure, while a spring hanger has very little stiffness in comparison and passes almost none. Hang the pump's discharge pipe on hard clevises right off the flex connector, and the pipe carries the vibration past your flexible break and dumps it into the building through the first hanger. So the first several hangers off the equipment are resilient, sized for the pipe weight including water, and the duct off a fan gets isolated hangers for its first run as well.

The flexible connector and the isolated hangers work as a pair. The connector breaks the direct path at the equipment; the isolated hangers keep the pipe and duct from becoming a new path a few feet downstream. Skip the hangers and you have moved the short-circuit, not removed it.

Seismic restraint on isolated equipment

Isolated equipment still needs seismic restraint, and the two systems do different jobs. The isolators let the equipment move so it does not transmit vibration; the seismic restraint keeps it from moving too far and tearing loose in a quake. A free spring with nothing to catch it lets the machine bounce off its mounts in an event, so in seismic zones the isolators are restrained, with snubbers or restrained-spring housings, sized to the seismic load.

The principle, repeated from the restrained-spring section, is that the restraint must not interfere with the isolation during normal running. The snubber gaps are set so the equipment runs free on its springs and the restraint engages only when a shock drives the equipment past its normal travel. A snubber adjusted tight against the equipment is touching it all the time, which carries vibration through the snubber and shorts the isolator, the same failure as any other rigid bridge.

Seismic design of the anchorage and the restraint is engineered to the local code and the equipment, and the full treatment belongs to the seismic restraint topic. The point to carry here: isolation and restraint are both required on the same equipment, they are set up so the restraint is idle in normal operation, and a restraint left touching the running equipment defeats the mounts it was meant to protect.

Chiller and large-equipment isolation

Chillers are heavy, often slow, and frequently sit in a penthouse or a mechanical floor over occupied space, which makes them prime candidates for spring isolation. A large centrifugal or screw chiller on an upper floor commonly rides on spring isolators selected for the floor span, sometimes restrained springs where seismic or wind governs. The compressor and the machine's running speed set the disturbing frequency, and the spring deflection is picked to stay well below it.

Two chiller-specific traps. The operating weight is not the shipping weight: a chiller full of refrigerant, water, and oil weighs more than the empty machine that came off the truck, and the isolators have to be selected and adjusted for the operating weight so they sit at the right deflection running, not crushed or barely loaded. And the springs are often shipped with the equipment blocked or bolted down for transit. Those shipping restraints have to come out and the isolators have to be released and leveled at startup, or the chiller runs hard-mounted on locked springs and isolates nothing.

The piping off a chiller is large and rigid, so the flexible connectors and the isolated hangers matter as much here as anywhere. Big pipe is a big path. Float the machine, break the pipe connections, and isolate the first hangers, or the chilled and condenser water lines will carry the compressor's signature into the building.

Fan and AHU isolation

Fans and air handlers come two ways: internally isolated, where the fan and motor sit on springs inside the cabinet and the cabinet bolts down, or externally isolated, where the whole unit rides on isolators under its base. Know which one you have before you add mounts. Putting external springs under a unit that is already internally isolated stacks two soft systems and can let the cabinet wallow; hard-mounting a unit that was meant to be externally isolated transmits everything. The submittal tells you which scheme the unit is built for.

Fans also produce thrust. A centrifugal fan pushes air, and the reaction pushes the fan the other way, a steady force on top of the rotating imbalance. On a flexibly mounted fan that thrust would let the assembly shift and pull on the duct connection, so thrust restraints are added, springs set horizontally to take the push while still allowing the fan to isolate vertically. The flexible duct connection at the fan inlet and outlet is what keeps that movement off the duct, and it has to have enough slack to actually flex, not be pulled drum-tight.

The air handling unit guide walks through the unit section by section. The mounting point here: confirm internal versus external isolation, add thrust restraint where the fan needs it, and never let the flexible duct connection get installed so tight it becomes a rigid link.

Pump isolation

A pump on a hydronic loop is the textbook isolation assembly: the pump on an inertia base, the base on spring isolators, and flexible pipe connectors at the suction and discharge. The inertia mass steadies the pump and gives the springs something heavier to isolate; the springs drop the natural frequency below the pump's running speed; the flex connectors keep the vibration off the rigid pipe. Then the first several pipe hangers on the suction and discharge are resilient, so the vibration does not re-enter through the pipe a few feet away.

Inline circulators are lighter and faster and often need only neoprene or smaller spring mounts, sometimes isolated through the pipe supports rather than a base. The selection follows the same logic: weight, speed, and floor location set the deflection.

This is covered end to end in the hydronic pump installation guide, including the suction piping and alignment that keep the pump from making vibration in the first place, so go there for the pump specifics. The isolation point is the assembly: base, springs, flex connectors, isolated hangers, all designed together. Leave out any one and the others cannot carry the load alone.

What short-circuits a vibration isolator?

A short circuit is any rigid path that bridges across the isolator and carries the vibration straight into the structure, past the soft mount that was supposed to stop it. It is the number one field failure in vibration isolation, and it is almost always an install or a housekeeping problem, not a design one. The springs are right, the selection is right, and one hard bridge throws it all away.

The usual culprits. A rigid pipe, duct, or conduit run hard to the equipment with no flexible connector, the most common one by far. A bolt run down tight so the spring is fully compressed and cannot move, or an anchor that clamps the equipment to the deck through the isolator. Debris under the base, a chunk of grout, a dropped tool, a hardened glob of mortar, a cut-off of conduit, bridging the gap and touching both the equipment and the floor. A snubber or seismic restraint adjusted so it touches the running equipment. Paint or grout that ran into the gap and set up solid. A shipping bolt or shipping bracket left in place from the factory.

The tell is simple and the check is fast: there should be daylight and free movement across every isolator, and nothing rigid spanning it except the isolator itself. Run a hand or a light around the base. If the equipment is touching anything besides its mounts and its flexible connections, that contact is carrying vibration, and it is doing it whether anyone notices or not. Find the bridge and break it.

This is the failure to look for first, before you doubt the spring selection. A perfectly selected isolator that is shorted out performs exactly like no isolator at all.

Leveling and even loading

Isolators have to be leveled and evenly loaded, with the equipment sitting level and each mount carrying its share. A spring isolator deflects in proportion to the load on it, so if one corner is heavy and another is light, the springs compress unevenly, the equipment sits cocked, and the mounts are working at different points on their travel. The heavily loaded one can be near solid while the light one is barely engaged, and neither is at the deflection the selection assumed.

Free-standing springs usually have a leveling adjustment, a bolt that sets the operating height so you can bring the equipment level and balance the load across the mounts. Set them with the equipment at operating weight where you can, since that is the load the deflection was picked for. Check that each spring is compressed roughly the same amount and that none is coiled solid or barely touched.

Uneven loading also walks equipment and stresses the connections. A pump that sits unlevel pulls on its flex connectors at an angle and loads its bearings off-axis. Level it, balance the springs, and confirm the operating height matches what the isolator schedule called for before you sign off.

Commissioning the isolation

Commissioning the isolation is a short list of physical checks plus a running observation, and it is the step that catches the shorts before they become callbacks. Walk every isolator with the equipment running and look for the things that defeat it.

Confirm the isolators are free and not bottomed: the springs have travel left, the gap is open, nothing is solid. Confirm the shipping restraints are removed and the isolators are released and leveled. Confirm every connection that lands on the equipment is flexible, pipe, duct, conduit, drain, with enough slack to actually move. Look and feel for any rigid contact across the mounts, debris under the base, grout in the gap, a snubber touching, a tight bolt. Then run the equipment and feel the structure: a hand on the floor or the nearby pipe and duct will tell you fast whether vibration is getting through, and where.

Where the spec calls for it, a vibration measurement on the equipment and on the structure quantifies what the hand tells you and confirms the isolation is doing what the design intended. On sensitive jobs that measurement is the acceptance, and it is worth doing before the building is occupied, because finding it loud now is cheaper than chasing it quiet later.

Isolation, room noise, and the harder locations

Vibration isolation is one half of a quiet mechanical space; the other half is the airborne and duct-borne noise that sets the room's noise criteria, its NC level. Isolation kills the structure-borne path, the rumble that comes up through the floor and the pipe. It does nothing for the noise that travels down the duct from the fan to the diffuser, or the noise that radiates off the equipment and the duct into the room. A space that meets its NC target needs both: the equipment isolated from the structure, and the duct, diffuser, and equipment noise controlled by silencers, lining, and layout.

This is where the room NC, the duct design, and the isolation scheme come together, and it is a topic of its own. The mounting point is that isolation and noise control are complementary, not interchangeable. You can isolate a fan perfectly and still fail the NC target because a diffuser is whistling, and you can quiet the diffusers and still feel the chiller through the floor because the isolation was shorted.

Two scenarios push isolation hard. Equipment on a roof over occupied space, where the deck is light and the structure-borne path is short and direct, and equipment in or around a data center or other sensitive space, where the floor and the served space can be unusually intolerant of vibration. Both lean on the same fundamentals: deflection picked for the floor, every path broken, nothing shorting the mounts. The stakes are just higher, so the selection and the field checks get more attention, and the vibration measurement usually becomes part of acceptance.

What to document

Months after signoff, a rumble shows up in a room two floors down, and someone has to work out whether the mounts were ever set right. Record what was installed on each piece of equipment, so the next person can check it against the schedule instead of guessing.

Capture the equipment and its location and floor, the isolator type and the specified deflection, the base if any, the flexible connections installed, the seismic restraint, and the commissioning result including any vibration reading. If a shipping restraint was removed, note it, because that is the one a service tech months later cannot tell from the ground.

Common mistakes

• Isolator short-circuited or bottomed out by a rigid bridge, debris in the gap, or a tightened bolt. The number one failure.
• No flexible connectors on the pipe, duct, or conduit, leaving a hard path that carries vibration past the mounts.
• Wrong deflection for the location, often a grade-level detail reused on an upper floor over occupied space.
• No inertia base where the equipment needs the mass, so a pump or large fan walks on its springs.
• Equipment unlevel or the springs unevenly loaded, so the mounts work at the wrong point on their travel.
• Seismic restraint or snubber adjusted tight against the running equipment, shorting the isolator it was meant to protect.
• Shipping bolts or shipping brackets left in place, so the equipment runs hard-mounted on locked isolators.
• Mounting equipment to a housekeeping pad as if the concrete were the isolator.

Field checklist

Standards and references

The framework for HVAC vibration isolation lives in the ASHRAE Handbook, mainly the noise and vibration control chapter in the Applications volume, which gives the theory, the isolator selection by equipment and floor, and the deflection guidance the schedules are built from. ASHRAE describes isolator types in a numbered scheme, neoprene mounts, spring mounts, restrained spring mounts, thrust restraints, and air mounts, that you will see referenced on isolation drawings and submittals. Treat the deflection and selection figures as guidance to confirm against the specific equipment and project, not as fixed numbers.

The isolator manufacturer is the other authority. The selection tables, the deflection ratings, the operating-height and snubber-gap settings, and the base sizing come from their data for the actual product, and they govern the install over any rule of thumb. SMACNA covers the duct construction and the flexible duct connection detail. The structural engineer governs the seismic anchorage, the restraint loads, and what the floor can carry, and the seismic restraint design is theirs and the local code's.

Cite the source that controls the point. ASHRAE for the framework and the selection approach, the manufacturer for the product's deflection and settings, SMACNA for the duct connection, and the structural engineer and the adopted code for the seismic anchorage. And whatever the tables say, the field rule does not change: keep the natural frequency well below the operating speed, break every rigid path with a flexible connection, and never let a bolt, a snubber, or a piece of debris short the isolator out.

Units, terms, and conversions

Vibration isolation carries a few terms that show up across the schedule, the submittal, and the manufacturer's data, and they are worth keeping straight because a wrong reading of deflection or frequency throws the selection off.

Static deflection is in inches in the isolator tables and millimeters in metric data. Frequency is in hertz, cycles per second, or sometimes cycles per minute to match equipment rpm, so a fan at 1,200 rpm is 20 Hz. Isolation efficiency is a percent, how much of the force the mount keeps out of the structure. Watch the difference between operating weight and shipping weight, because the isolators are selected for the equipment running and full, not empty on the truck.

Static deflection

How far the isolator compresses under load; sets the natural frequency and the isolation

Natural frequency

The rate the equipment-on-mount system bounces at; kept well below the operating speed

Disturbing frequency

The frequency of the force the equipment makes, set mainly by running speed

Isolation efficiency

The percent of the equipment's vibration force the isolator keeps out of the structure

Inertia base

Concrete-filled frame that adds mass under the equipment on top of the isolators

Housekeeping pad

Raised concrete pad the equipment or its isolators sit on; a mounting, not an isolator

Short circuit

Any rigid path bridging the isolator that carries vibration into the structure

Thrust restraint

Spring restraint that takes a fan's air thrust while still isolating vertically

Related tools

Calculators and readiness checks for this work

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