A Shot of Vib Isolation

8/22/2019 A Shot of Vib Isolation

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A SHOT OF ISOLATION TO PREVENT AN

OUTBREAK OF VIBRATION

Presented By:

Robert Simmons, PE

ASHRAE 2006 Winter Meeting, Chicago

Seminar 11

AMBER/BOOTH COMPANY


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STRUCTURE BORNE VIBRATIONINDUCED BY MACHINERY

OBJECTIONABLE

VIBRATION TRANSMITTED

THROUGH STRUCTURE

COOLINGTOWER

Vibration interferes with precision equipment


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Components of Vibration Transmission

Machinery Generating Vibration

F Cooling Towers, Motors, Fans, Pumps, AHU, Water flow,

etc....F PipingF Large and small

Medium Through Which Vibration is Transmitted

F Most bldg. components (floors, beams, columns, walls, etc)F Pipe

F Resonant conditions can amplify the vibration

F An isolation systemmust be used to block the path

The OccupantF Building owners and tenants demand for comfortable work

space. Quality of workplace affects worker production

F Quality of classroom affects student learning

F High - tech equipment in hospitals or micro-electronic

RECEIVER

PATH

SOURCE


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Sou rce Vs. Receiver

VIBRATION SOURCE IS 10 TO 1000 TIMES ACCEPTABLE LEVELS

High tech. receiver can onlytolerate 0.00013 to 0.006 in./sec

Rotating equipment createsvibration from 0.08 to 0.2 in./sec

Mechanical Source


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A VIBRATION ISOLATION SYSTEM CUTS OFF THE TRANSMISSIONPATH AND PREVENTS VIBRATION PROBLEMS

A PENNY OF PREVENTION IS WORTH A POUND OF CURE

NO STRUCTURE BORNE VIBRATION

NO OBJECTIONABLE

VIBRATION TRANSMITTEDTHROUGH STRUCTURE

COOLINGTOWER

SPRING ISOLATION BASE

SPRING ISOLATION FOR PIPE

ISOLATED CONCRETE INERTIA BASE


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KEYS TO PRESCRIBING AN EFFECTIVE

ISOLATION SYSTEM

F DETERMINE HOW MUCH ISOLATION IS REQUIRED

How much static deflection is required to eliminate source vibration

Greater deflection = Greater Isolation

F ISOLATOR TYPE

Spring, Elastomeric, Air spring

F LOCATION & SUBSTRUCTURESlab on grade, Non-sensitive area

Upper level (10-30span), Sensitive areaCritical area (30-40span), Lightweight / Flexible construction

F SUPPORT METHOD

Floor mount, HangingPoint load, Base, Rail, Concrete Inertia Block

Wind and Seismic Restraint


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1st Determine the vibration frequency

Frequency(fd) = RPM/60 = cycles/sec (cps)

= Hertz (Hz)

Mechanical Source

1 CYCLE

RPM


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2nd Determine the isolator natural frequency

Isolator Natural Frequency

F More deflection giveslower natural frequency


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Prescribe a low isolator natural frequency to rid

the equipment vibration


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Vibration Transmissibility Curve

FT = Transmissibility - Thefraction of vibration that

transmits through isolatorsto structureFResonance = The range of

fd/fn where vibration isamplified

FT = 1/[1- (fd/fn)2 ]Lower natural frequency

giveslower transmissibility


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Transmissibility Quick Reference Chart


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Isolators Types


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How much iso lat ion can be expected fo r

each type?

ISOLATOR

TYPE

STATIC

DEFLECION

(IN)

NATURAL

FREQUENCY

(CPM) (1)

350 500 650 800 1000 1200 1750 3600

2.5 119 13.07% 6.00% 3.47% 2.26% 1.44% 0.99% 0.46% 0.11%

1.5 154 ---- ---- 5.95% 3.85% 2.43% 1.67% 0.78% 0.18%

0.75 217 ---- ---- ---- 7.94% 4.94% 3.38% 1.56% 0.36%

0.5 375 ---- ---- ---- ---- ---- 10.82% 4.81% 1.10%

0.375 430 ---- ---- ---- ---- ---- ---- 6.43% 1.45%

ELASTOMERIC

PAD0.15 680 ---- ---- ---- ---- ---- ---- ---- 3.70%

NOTES:

1). Theoretical natural frequencies and transmissibility for elastomers have been adjusted for average inherent dampening.Note that the actual properties of elastomers may vary considerably. Elastomeric isolator manufacturing should be consulted.

2). Applies to open or housed spring. Housed springs must have sufficient clearance to avoid "short out" of spring.

TABLE 1- TYPICAL TRANSMISSIBILITIES FOR DIFFERENT ISOLATORS

ELASTOMERIC

MOUNT

PERCENT TRANSMISSION FOR DISTURBING

FREQUENCIES (CPM)(1)

STEEL SPRING (2)

Design Transmission for Critical:


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Effect of location and substructure

POOR

BETTER

BEST


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ASHRAE

APPLICATIONS

HANDBOOK

CHAPTER 47

SELECTION GUIDE


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TYPICAL APPLICATIONS AND

CASE STUDIES


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Open spring isolator for AHU: 1-1/2 deflection


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Open spr ing appl icat ion w ith angle base


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T-shape base to support pipe elbows

Compressor with large unbalanced forces


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Compressor with large unbalanced forces


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Typical Cooling Tower Isolation


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RESTRAINED SPRING ISOLATORS


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Chiller


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Iso lated Pipe


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Typical Pipe Hangers


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Combination Spring/Elastomeric Hanger


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Suspended Equipment


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Angularity hangers allow misalignment


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Riser Pipe Suppo rt

R ft U it


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Rooftop Units


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Isolation rail for roof curb


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Case 1: Failed instal lat ion on roof of hosp ital with no isolat ion


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Case 1: Successfu l retrof i t solv ed noise problem. RETROFITCOST EXTRA $10,000


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Case 2: Successful retrof i t solved operat ing room prob lem.


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Case 3: Successful retrof i t solved laser lab p roblem .


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Case 4: Successful retrofit solved building glass vibration problem.


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SUMMARY

Vibration is a real problem in todays hospital

and high tech industries.

Prescribe the proper isolation to prevent

vibration interference with important equipment.

A PENNY OF PREVENTION IS WORTH A POUND OF CURE

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A Shot of Vib Isolation