Operating manual – DualPAC with reciprocating compressors
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4.2.4
Vibration dampers
The number of vibration dampers is adapted to each specific DualPAC unit. For installation on sol-
id concrete floor, anti-vibration machine feet are sufficient. Such machine feet are designed for
minimum 70% vertical isolation (100% capacity).
For installation on decks, special dampers are often required. Please consult a vibration expert or
a Johnson Controls representative for further information.
To ensure optimum effect of each individual anti-vibration machine foot, the load on the feet must
result in roughly the same deflection of all machine feet, see Fig. 21. Deflection of a machine foot,
type TF, can be adjusted by increasing or reducing the load compared to the other supports by
turning the adjusting rod.
Fig. 21: Anti-vibration machine foot
4.2.5
Variable speed drive
A reciprocating compressor where the motor drive speed is controlled by a frequency inverter is
also called a rotatune compressor in UniSAB terminology. See the UniSAB III Engineering manual
for further description.
For some DualPAC models with reciprocating compressors, mechanical vibrations caused by reso-
nance may occur in the actual operating range 500-1800 rpm. This will in some cases result in an
increased vibration level over an interval of approximately 100-150 rpm. As a rule of thumb the
rpm area is skipped if the vibration level exceeds the recommended maximum vibration level
(see the compressor manual).
All DualPAC units are tested from factory. If skipping of rpm is required, this has been done and
noted in the vibration report.
It is recommended to check the vibration level during pre-start. The resonance rpm area may
change after shipping and installation.
4.3
Secondary system
4.3.1
General information
Designing a secondary system is a complex task where many things must be considered, for
example:
•
load variations
•
pressure loss
•
service
•
maintenance
•
corrosion
•
fouling.
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