070.750-IOM2 (JUN 22)
Page 9
HPS 273 and 407 Rotary Screw Compressor
Installation - Operation - Maintenance
• In CO
2
applications using miscible oil types POE and
PAG, it is critical to keep water content to the lowest
possible. Down to 10 ppm is the goal. The installation
must have large lter dryers with replaceable elements
that you can effectively service and vacuum dry before
putting back into service.
• If the temperature difference becomes greater than or
equal to 250°F (138.9°C) between suction and dis-
charge, unload the slide valve to less than 50% but
above 40%.
• The minimum discharge temperature must be at least
54°F (30°C) above the actual dewpoint of the discharge
gases. This applies to part load conditions and full load
operation.
Vibration and sound data
The rotors balance grade is G 2.5 according to ISO 1940.
The male rotor drive end of the HPS 273
and 407
com-
pressors is keyless.
Effective vibration velocity must not exceed 8 mm/s RMS
(0.32 in./s) anywhere on the compressor. Alarm level is 12
mm/s RMS (0.47 in./s).
Table 6: Number of rotor lobes
Male rotor lobes Female rotor lobes
6 8
Table 7: Critical frequencies
Driver speed, rpm
3,000 3,600 4,200
Exiting member and event Main exciting fre-
quencies (Hz)
Male rotor, rotational, rst order 50 60 72
Male rotor, rotational, second order 100 120 144
Female rotor, rotational, rst 37.5 45 54
Female rotor, rotational, second 75 90 108
Discharge gas pulsation, rst 300 360 432
Discharge gas pulsation, second 600 720 864
Vibration level on the package can be higher, especially
on piping elements, and when the natural frequency of an
element falls together with one of the exciting frequen-
cies. If the vibration level gets too high, a skip frequency
function in the control system activates. After activating,
the motor runs through the critical speed very fast, not
causing any continuously high vibration.
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