Measurement report:
Elastic bearing for compressors
Effective vibration isolation with Getzner Isotop®

Complete unit

Decoupled reciprocating compressor

Measuring point on the f loor next to the unit

Construction

Benefits

In order to compare the insulation behaviour of different elastic bearings, vibration measurements werecarried out on a compact unit. The main excitation
came from a GEA Bock refrigerant compressor, whose
mass, including the attachments and oil, was around
80 kg (see fact box).

— Measurable reduction of vibrations inwa wide frequency range and thus reductionof secondary airborne noise— Unit installation also possible in criticallocations— Easy and convenient installation— Long service life and maintenance-free

For the purpose of the measurement, the compressor
was operated at the frequencies 30 Hz, 50 Hz and
70 Hz. The fan runs at an intensity of 30 % and serves
to balance the temperature of the refrigerant system,
although this component does not emit any measurable vibrations at this low level of utilisation.
For the comparison of the different elastic bearings,
a measuring point was selected on the floor directly next to the unit. This also allows conclusions to bedrawn about secondary airborne noise.

Fact box
Type:

Pmax:
Vth:
Weight:

GEA Bock
Reciprocating piston compressor
Semi-hermetic
HGX22P/160-4S
18/28 bar
13.7 m3/h
80 kg

Investigated bearing types
Different types of bearings were fitted, in order to obtaina meaningful comparison. The reference product is aconventional metal-rubber bearing, which is normally installed in the test unit as standard. In addition, measurements were carried out with steel springs and metalpolyurethane combinations.

Also investigated was the influence of an additional intermediate plate weighing 22 kg – i.e. roughly 27 % of thecompressor weight – on the insulating effect. This measurement was performed with Isotop® MSN-DAMP andIsotop® Compact.

Conventional rubber-metal
bearing

Isotop® MSN

Isotop® DMSNIsotop® DZE Mini

Isotop® MSN-DAMP

Isotop® Compact

Isotop® MSN-DAMP withadditional mass

Isotop® Compact withadditional mass

Measurement results
Direct bearing comparison
For the comparison of the different bearing types,
an operating frequency of 50 Hz was selected on thefrequency converter of the compressor. At this operating point, the direct bearings demonstrate a significant improvement in the insulating effect of up to12.3 dB compared to the conventional rubber-metal element. Attention must also be paid to stability and sturdiness of compressors. Here, steel spring solutions withSylodamp® damper cores (Isotop® DMSN) or elementswith a polyurethane core (Sylomer®/Sylodyn®) are preferable to pure steel springs.

Improved insulating effect in comparison to conventional rubber-metal bearings
20 dB
18 dB
16 dB
14 dB
12 dB

12.3 dB

10 dB
8 dB

9.1 dB9.4 dB

Isotop® MSN

Isotop® Compact

10.6 dB

11 dB

Isotop® MSN-DAMP

Isotop® DMSN

6 dB
4 dB
2 dB
0 dB

50 Hz

Isotop® DZE Mini

Compressor operating frequency: 50 Hz Measuring point: Floor

Influence of additional intermediate plate
When designing an elastic bearing arrangement, it
is important to focus on the selection of the correct
bearing elements. The capacity of the elastic Isotop®
elements should be at least 70 %. The dynamically effective mass is increased by fitting additional metal

plates beneath a refrigerant compressor. This reduces
the natural frequency of the elastic bearing, because its
capacity is optimally utilised. For example, the capacity of the Isotop® Compact was increased from 74 % to95 % by the additional mass and a further 2.5 dB improvement in the insulating effect was achieved.

Additional improvement of the insulating effect with an intermediate
plate compared to conventional rubber-metal bearings
20 dB
18 dB
16 dB
14 dB
12 dB
10 dB

11.9 dB

12.4 dB

Isotop® Compact withintermediate mass

Isotop® MSN-DAMP withintermediate mass

10.6 dB
9.4 dB

8 dB
6 dB
4 dB
2 dB
0 dB

Isotop® Compact
50 Hz

Isotop® MSN-DAMP

Compressor operating frequency: 50 Hz Measuring point: FloorImpact excitations show that the floor has a natural
frequency at about 70 Hz. Nevertheless, a significant
improvement was also achieved in this range.

Results over all three operating frequenciesof the compressor
If the previous bearing comparison is extended to include the further operating frequencies of the compressor of 30 Hz and 70 Hz, a significant improvementin the insulating effect compared to the conventionalrubber-metal bearing is also demonstrated here.

Improved insulating effect when compared to conventional rubber-metal bearings
20 dB
18 dB
16 dB
14 dB
12 dB

14dB

13.7
dB

10 dB
9.1
dB

8 dB
6 dB

7.6
dB

4 dB

11dB

10.6
dB

9.4
dB

8.9
dB

13.7
dB

6.3
dB

11.9
dB
9.3
dB

7.2
dB

8dB

11.3
dB

12.3
dB

11.6
dB
9dB

12.4
dB
9dB

6.8
dB

2 dB
0 dB

30 Hz

Isotop® Compact

50 Hz70 Hz

Isotop® MSN-DAMPIsotop® DMSN

Compressor operating frequency: 30, 50, 70 Hz

Isotop® Compactwith intermediate mass

Isotop® DZE Mini

Isotop® MSN-DAMP
with intermediate mass

Measuring point: Floor

Put us to the test!
Every unit is different. And the structure and foundation also differ.
We would be delighted to support you in selecting the right bearing
for your unit or in conducting measurements!

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