Vibration isolators for machinery · Spring vs elastomeric, static deflection and natural frequency, reserve deflection, horizontal stability, rubber loading and hardness
A vibration isolator is a spring or elastomer mount placed between a vibrating machine and its support so that the machine's vibration is not passed on to the structure. Ask three things first: the machine's weight distribution and lowest operating speed, the static deflection needed to isolate that speed, and whether springs, elastomers or both suit the load, environment and any restraint needs.
Spring, elastomeric and combined isolators, mounts and hangers for motors, pumps, fans, compressors, vibrating machinery and building services equipment. Cable vibration dampers for overhead lines, shock absorbers for vehicles, and active isolation tables are outside this page.
01
The University of Houston's facilities master specification for vibration isolation (section 23 05 48) requires spring isolators for all equipment driven by motors of 3 hp and larger, and elastomeric mounts or hangers sized for ½ in deflection for equipment driven by motors of 2 hp and smaller, unless noted otherwise. It treats listed deflections as minimums, leaving the isolation manufacturer to determine the spring deflection needed to prevent objectionable vibration and meet the noise criteria, and requires all isolators under a given piece of equipment to be selected for approximately equal deflection. [1]
Editorial calculation (simple spring-mass physics): natural frequency fn ≈ 15.76 ÷ √(static deflection in mm) Hz, so ½ in (12.7 mm) gives about 4.4 Hz, 1 in (25.4 mm) about 3.1 Hz and 2½ in (63.5 mm) about 2.0 Hz. Isolation only begins once the forcing frequency exceeds about √2 times fn; a motor at 1,450 rpm (24.2 Hz) on ½ in mounts runs at about 5.5 times fn. [1]
Give the supplier the machine weight and centre of gravity, number of support points, lowest operating speed, required isolation or deflection, location (floor, roof, outdoors, seismic zone), base or inertia block arrangement, and environment (oil, temperature, weather).
02
The specification requires spring isolators to be completely stable in operation with at least 30% reserve deflection beyond operating conditions (springs capable of 30% over-travel before becoming solid), and horizontally stable with a horizontal-to-vertical spring-rate ratio kx/ky of at least 1.2 times the static deflection divided by the working height. Elastomeric isolators and components must be neoprene or high-quality synthetic rubber with antioxidant additives, sized for a maximum load of 60 psi at 40 durometer; open spring mounts carry a bonded ¼ in neoprene pad of that grade under the base plate. [1]
It also lists isolator types: free-standing open and enclosed spring mounts with levelling bolts, aluminium-housed and restrained spring mounts, and spring or combination spring-and-elastomer hangers whose steel boxes withstand 200% overload without visible deformation; isolators for outdoor equipment must restrain it under normal wind and withstand wind loads of 50 lb/ft². [1]
Mason Industries' guide specification for its unhoused SLF spring mounts sets tighter stability and travel figures: springs free-standing and laterally stable without a housing, a ratio of spring diameter to compressed spring height of no less than 0.8, a minimum additional travel to solid equal to 50% of the rated deflection, a moulded neoprene cup or ¼ in (6 mm) neoprene acoustical friction pad between base plate and support, levelling bolts rigidly bolted to the equipment, and equal installed and operating heights. It asks that submittals include spring diameters, deflection, compressed spring height and solid spring height. [3]
Editorial calculation: for a 1 in (25.4 mm) rated deflection, Mason's 50% travel to solid means at least 12.7 mm more travel before the coils close, against 7.6 mm under the 30% reserve in the University of Houston specification; a spring compressed to 100 mm working height needs a diameter of at least 80 mm to meet the 0.8 ratio. Compare both rules when two specifications apply. [3] [1]
Qingdao Todo Rubber, a supplier linked to this page, lists rubber vibration isolators, mounts, shock absorbers, pump dampers with threaded studs and rubber-metal bushings. [2]
03
Mason's SLF guide specification above describes unhoused springs that must be laterally stable on their own. Where the supported equipment can move sideways, makers offer housed mounts instead. nVent CADDY's housed spring mount VIBHSM2A500 is listed at 2 in deflection and 500 lb, for HVAC equipment, generators, compressors, pumps, chillers and cooling towers where lateral movement is anticipated. Its listed features are a powder-coated cast iron housing, colour-coded spring elements for selection and field verification, a rubber pad that gives anti-skid properties, a rubber snubber that prevents metal-on-metal contact, and a built-in levelling device for fine adjustment. [4] [3]
Editorial calculation: 500 lb at 2 in deflection is a spring rate of about 250 lb/in (about 4.5 kg/mm), and 2 in (50.8 mm) of static deflection gives a natural frequency of about 15.76 ÷ √50.8 ≈ 2.2 Hz, against about 4.4 Hz for the ½ in elastomeric mounts in the University of Houston specification. The deflection is only reached at the rated load, so a mount loaded to half its rating deflects about 1 in and runs at about 3.1 Hz; ask the supplier to select each spring for the actual corner load. [4] [1]
Editorial note: the University of Houston specification asks for all isolators under one machine to be selected for approximately equal deflection, and the colour coding on the CADDY springs is one way to check on site that the specified spring went under each corner. [1] [4]
| Data point | Housed mount (nVent CADDY VIBHSM2A500) | Unhoused mount (Mason SLF guide specification) |
|---|---|---|
| Lateral restraint | Cast iron housing with rubber snubber [4] | Spring laterally stable without housing; diameter ÷ compressed height ≥ 0.8 [3] |
| Rated deflection and load | 2 in at 500 lb [4] | Per submittal; travel to solid ≥ 50% of rated deflection [3] |
| Base | Rubber anti-skid pad [4] | Moulded neoprene cup or ¼ in neoprene pad [3] |
| Levelling | Built-in levelling device [4] | Levelling bolts bolted to the equipment [3] |
04
The suppliers linked to this page list vibration isolators or rubber mounts; their cards link to the pages reviewed.
Ask any supplier for rated load and static deflection at that load, spring rate (vertical and horizontal), natural frequency, elastomer compound, hardness and temperature range, reserve deflection, restraint and limit-stop features, corrosion protection and the selection calculation for your machine.
05
This is a functional reference built from the sources cited; it is not one maker's specification.
| Part | Role | Fix in the order |
|---|---|---|
| Coil spring | Provide low vertical stiffness. [1] [3] | Deflection; reserve; kx/ky; diameter-to-height ratio. |
| Elastomer element or pad | Isolate and damp; ¼ in neoprene pad under spring base. [1] [2] [3] | Compound; hardness; load psi. |
| Housing or base plate | Carry and locate. [1] | Material; finish. |
| Levelling bolt | Set equipment height. [1] | Adjustment. |
| Restraining bolts or limit devices | Limit movement, e.g. under wind load. [1] | Restraint rating. |
06
An isolator quotation needs values for your machine. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.
| Field | What it means and published values | Ask the supplier for |
|---|---|---|
| Rated Load Capacity (kg) | Load per isolator. | Rated load. |
| Natural Frequency (Hz) | From static deflection (editorial: ½ in ≈ 4.4 Hz). [1] | fn at your load. |
| Transmissibility | Editorial: below 1 once forcing frequency exceeds √2 × fn. | Value at operating speed. |
| Damping Ratio | Elastomer or damper. | Value. |
| Maximum Static Deflection (mm) | e.g. ½ in elastomer; spring with 30% reserve, or 50% travel to solid. [1] [3] | Deflection, reserve, solid height. |
| Operating Temperature Range (°C) | Elastomer limits. | Range. |
| Elastomer Hardness (Shore A) | e.g. 40 durometer. [1] | Hardness. |
| Elastomer Material | Neoprene or synthetic rubber with antioxidants. [1] | Compound. |
| Housing Material | Steel or aluminium housings. [1] | Material; corrosion protection. |
| Dimensions (L×W×H) (mm) | Working height affects stability; spring diameter ≥ 0.8 × compressed height. [1] [3] | Spring diameter; compressed and solid height. |
| Weight (kg) | Mass. | Mass. |
| Mounting Hole Diameter (mm) | Bolting. | Hole size. |
07
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Machine: [weight; centre of gravity; support points] Speed: [lowest operating speed] Isolation: [deflection or efficiency] Type: [spring; elastomer; hanger] Site: [floor; roof; outdoors; seismic] Environment: [oil; temperature; weather]
These companies list vibration isolators or rubber mounts.
Lists rubber vibration isolators, anti-vibration mounts and shock absorbers.
Product scope checked 2026-10-11
Lists vibration isolators with industrial fans.
Product scope checked 2026-10-11
Lists moulded rubber products including vibration mounts.
Product scope checked 2026-10-11
Lists rubber moulding including vibration isolation mounts.
Product scope checked 2026-10-11
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
The University of Houston specification uses springs for equipment driven by motors of 3 hp and larger and elastomeric mounts sized for ½ in deflection for 2 hp and smaller. [1]
At least 30% beyond operating conditions, with springs able to over-travel 30% before going solid. [1]
The specification calls for neoprene or synthetic rubber at 40 durometer, loaded to no more than 60 psi. [1]
Mason's guide specification requires spring diameter at least 0.8 times the compressed height and travel to solid of at least 50% of rated deflection. [3]
nVent CADDY lists its 2 in, 500 lb housed spring mount for HVAC equipment, generators, compressors, pumps, chillers and cooling towers where lateral movement is anticipated, with a cast iron housing and rubber snubber. [4]
Sources checked 2026-10-12. The University of Houston's master specification is owner design guidance for building services; Mason Industries and nVent CADDY publish their own spring-mount data; Todo Rubber is a supplier linked to this page.
Ask for use case, specification boundaries, supplier type, and RFQ preparation information for this product.
Compare manufacturer profiles with relevant product and process capability.