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Casa / Casos / Rubber Vibration Isolator Engineering Case Study

Rubber Vibration Isolator Engineering Case Study

2026-10-14
mais recente caso da empresa sobre Rubber Vibration Isolator Engineering Case Study
Case Detail

  1. Executive Summary

Core judgment: For pumps running at 2,900 r/min, shear-type or spring–rubber composite rubber isolators are a viable and economical choice. Controlling selection with a frequency ratio r = f/f0 ≥ 2.5 and targeting r ≈ 5 brings theoretical transmissibility down to about 4% and isolation efficiency to about 96%; combined with an inertia base and flexible pipe connections, structure-borne sound to adjacent rooms is markedly reduced.
Conclusion: This case can be executed through the workflow “measure speed → calculate frequency ratio → select model by load → install with inertia base and flexible connections → re-measure and accept”. Rubber isolators with a rated load ≥ 400 kg per mount satisfy the vibration-isolation targets.
Basis:
  • GB 50019-2015 requires the ratio of equipment running frequency to isolator natural frequency to be ≥ 2.5, and recommends rubber or other elastic-material isolators when equipment speed exceeds 1,500 r/min.
  • The pump disturbing frequency f = 2,900/60 ≈ 48.3 Hz; with an isolator natural frequency of about 9 Hz, r ≈ 5.4, giving a theoretical transmissibility of about 3.6%, an isolation efficiency of about 96.4%, and a force transmission reduction of about 28.9 dB (undamped formula).
  • Industry retrofit case figures: pump-set vibration transmissibility can be reduced below 10%, with 20–30 dB noise reduction in areas adjacent to the pump room.
Constraints: The above calculations are based on an undamped single-DOF model; in practice rubber damping and secondary transmission through piping affect results, so field re-measurement governs. Small-load E-type rubber isolators have static deflections of only 0.6–0.9 mm and relatively high natural frequencies; per the code, low-speed equipment should use spring isolators instead.
Action: Implement per the workflow at the end of this document; acceptance is based on measured vibration velocity and noise, with records kept of isolator deflection and base levelness.

  1. Case Overview and Isolation Objectives

  1. Project Background

An HVAC plant room on the second floor of an industrial building houses two chilled-water pumps and two cooling-water pumps (2,900 r/min), with offices and a precision inspection area directly below. Pump vibration propagates through the floor slab and piping to adjacent rooms; field measurements showed excessive micro-vibration at the inspection bench and excessive noise in the office area, calling for a vibration-isolation retrofit of the pump sets. This document is a typical engineering case (equipment parameters and quantities are replaceable); all calculations and parameters are annotated with their source or basis.

  1. Isolation Objectives and Acceptance Criteria

Objective
Indicator
Target/Limit
Basis
Frequency ratio
r = f/f0
≥ 2.5, preferably 4~5
GB 50019-2015, Cl. 12.3.4
Isolation efficiency
I = 1 − T
≥ 93% (at r ≥ 4)
GB 50019-2015 commentary
Vibration transmissibility
T
≤ 0.1
Engineering practice / vendor case figures
Noise in adjacent rooms
Night-time equivalent level
≤ 35 dB(A)
GB 22337-2008
Sources: GB 50019-2015 “Code for Design of Heating Ventilation and Air Conditioning for Industrial Buildings”; GB 22337-2008 “Emission Standard of Environment Noise for Social Life” | Targets are common engineering values; follow project-specific requirements

  1. Vibration Source Analysis and Isolation Calculation

  1. Equipment Vibration Parameters and Isolation Form Selection

Equipment
Speed (r/min)
Disturbing frequency f = n/60 (Hz)
Code-recommended isolation form
Chilled/cooling water pumps
2 900
48.3
Rubber isolator or elastic-material pads (speed > 1,500 r/min)
Roof exhaust fan (comparison)
1 450
24.2
Spring isolator (speed ≤ 1,500 r/min)
Source: GB 50019-2015, Cl. 12.3.4; disturbing frequency computed as f = n/60

  1. Frequency Ratio and Transmissibility Calculation: r ≈ 5.4, Isolation Efficiency ≈ 96%

Disturbing frequency: $$f = n/60 = 2900/60 approx 48.3 mathrm{Hz$$
The natural frequency of the isolation system is determined by the isolator stiffness and the supported mass, and can be estimated from static deflection; shear-type/composite rubber isolators typically provide natural frequencies of 8–10 Hz. This case assumes $$f_0 = 9 mathrm{Hz$$.
Frequency ratio: $$r = f/f_0 = 48.3/9 approx 5.3$$
Undamped transmissibility: $$T = 1/(r^{2}-1) = 1/(5.37^{2}-1) approx 0.03$$
Isolation efficiency: $$I = (1-T) times 100% approx 96.4$$; force transmission reduction: $$R = 20 lg(1/T) approx 28.9 mathrm{dB$$

Fig. Transmissibility and isolation efficiency vs frequency ratio (calculated curve) | Basis: undamped single-DOF model T = 1/(r²−1), sampled at r = 1.5~10; GB 50019-2015 requires r ≥ 2.5, and its commentary notes efficiency >93% at r = 4~5, with diminishing returns beyond r = 5
Conclusion: r ≈ 5.4 falls in the “efficiency >95%” region, providing clear isolation with margin; avoid the amplification region r < 1.41 (√2) and the resonance region r ≈ 1.

  1. Isolator Selection

  1. Selection Principle: Match the Isolation Form to the Natural-Frequency Range

Per the selection ranges in the “Code for Design of Noise Control in Industrial Enterprises” and the GB 50019-2015 commentary, the isolator natural frequency must be sufficiently separated from the equipment disturbing frequency (r ≥ 2.5), and the isolation form is chosen by the target natural frequency:
Isolation form
Natural-frequency range
Typical application
Rubber isolation pad
10~20 Hz
High-frequency small equipment (1–2 layers)
Shear-type rubber isolator
5~12 Hz
Medium/high-speed pumps, fans, compressors (2–5 layers or shear type)
Metal spring isolator
2~5 Hz
Low-speed equipment ≤ 1,500 r/min
Air spring isolator
1~8 Hz
Precision equipment, large low-frequency disturbances
Source: isolation ranges from the “Code for Design of Noise Control in Industrial Enterprises” and GB 50019-2015 commentary | Shear-type rubber isolators and 2–5 layer rubber pads cover 5~12 Hz; 1–2 layer pads cover 10~20 Hz

  1. Load Calculation and Model Selection

The pump set (pump + motor + base) weighs about 1,200 kg; with 4 mounting points, the static load is about 300 kg per point. Applying a dynamic factor of 1.2 for starting impact gives a design load of about 360 kg per point.
Selection follows “rated load ≥ actual load, and deflection not exceeding 1/3–1/2 of the ultimate deflection”. Excerpts from the E-type rubber isolator parameter table (manufacturer-published values):
Model
Rated load Z (kg)
Static deflection at rated load (mm)
Dynamic stiffness Z (kg/cm)
Typical application
E25
25
0.9
750
Small instruments, fans
E60
60
0.7
1 600
Small pumps
E120
120
0.9
2 500
Small/medium equipment
E220
220
0.6
7 000
Medium equipment
E400
400
0.7
13 000
This case, per point (≥ 360 kg)
Source: Shanghai Huanxin Rubber Products E-type rubber isolator parameter table (manufacturer-published values) | Note: E-type isolators have small static deflection and a relatively high natural frequency, suiting high-speed small equipment; E400 meets the per-point load in this case, or a JG-type spring–rubber composite isolator can be used for a lower natural frequency and greater deflection

  1. Option Comparison: Rubber vs Spring vs Air Spring

Dimension
Rubber isolator
Metal spring isolator
Air spring isolator
Natural frequency
5~12 Hz (shear type)
2~5 Hz
1~8 Hz
Damping
High internal damping, good resonance control
Low damping, large resonance amplitude; combine with damping
Adjustable
Cost
Low
Medium
High
Environmental resistance
Sensitive to oil and heat; limited life
Durable; needs corrosion protection
Needs air supply and maintenance
Best suited to
Medium/high-speed equipment > 1,500 r/min
Low-speed equipment ≤ 1,500 r/min
Precision equipment, low-frequency isolation
Source: combined from code selection ranges and engineering experience

  1. Installation Implementation

  1. Base and Foundation

  • Use an inertia base (vibration-isolation base); where necessary, adopt a “floating double-isolation base”: a precast concrete slab placed between the equipment base and the floor, with rubber isolation pads beneath the slab, to lower the equipment center of gravity and shift the system natural frequency (GB 50019-2015, Cl. 12.3.8).
  • Position the equipment center of gravity as close as possible to the geometric center of the isolator array and keep the overall CG low; keep the foundation surface flat, isolator free heights uniform, and loading even and symmetric (Cl. 12.3.5).

  1. Isolator Installation Requirements

  • The design compression deflection of rubber isolators should be taken as 1/3–1/2 of the manufacturer's ultimate deflection; the load on any isolator must not exceed its allowable working load (Cl. 12.3.4).
  • After installation, check that deflection is consistent across all mounting points to avoid uneven loading; keep rubber parts away from oil, heat, and direct sunlight, and inspect periodically for aging.

  1. Flexible Pipe Connections and Structure-Borne Sound Control

  • Connect pump suction/discharge to the piping via rubber flexible connectors (flexible hose) to prevent rigid transmission of vibration and avoid intensified pipe vibration, and possible rupture, after the equipment is isolated (Cl. 12.3.6).
  • Install elastic pads between pipe supports/hangers and the piping; seal gaps where pipes pass through the plant-room enclosure with sound-insulating elastic material (Cl. 12.3.7).

  1. Performance Verification and Case Data

  1. Before/After Comparison (Industry Case Figures)

Indicator
Before retrofit
After retrofit
Data nature & source
Pump-set vibration transmissibility
Rigid connection, near 1
< 10%
Vendor case figures (JG-type solution)
Noise adjacent to pump room
Exceeded limits
Reduced 20~30 dB
Vendor case figures (HVAC pump retrofit)
Cleanroom vibration peak
Exceeded limits
Attenuated 90%, meets VC-C
Industry case report (fire-pump room retrofit at a semiconductor plant in Suzhou)
Metro station pump isolation efficiency
—
96.7%
Industry engineering report
Source: see references at the end of this document | Figures are vendor/engineering report claims (third-party), for reference only; acceptance for this case is based on field measurement
Conclusion: multiple case sources consistently show that code-compliant selection plus correct installation of rubber/composite isolation schemes reduces vibration transmissibility to below 10%, achieves isolation efficiency above 95%, and significantly reduces noise and micro-vibration in adjacent areas.

  1. Acceptance Conclusion

Recheck the calculation against GB 50019-2015 (frequency ratio ≥ 2.5) and re-measure vibration velocity, transmissibility, and adjacent-room noise after the retrofit: acceptance is granted when the targets are met. Simultaneously verify and record isolator deflection, base levelness, and the condition of flexible pipe connections.

  1. Lessons Learned and Notes

  • The frequency ratio is the primary control parameter: for r < √2 the isolator amplifies vibration; avoid the resonance region around r ≈ 1.
  • For low-speed equipment (≤ 1,500 r/min), rubber isolators may not provide a low enough natural frequency; switch to spring isolators per the code.
  • Isolation only addresses the “equipment–foundation” path; untreated piping, hangers, and wall penetrations create secondary sound paths that undermine the retrofit.
  • Rubber aging, oil, and heat change stiffness and damping; inspect deflection and appearance periodically.
  • Calculations use an undamped model; actual rubber damping ratios of about 0.05–0.15 suppress resonance amplitude, and the above formulas are adequate for engineering judgment.

  1. References