Notes On Replacing The Shaft Seal; Avoiding Liquid Shocks - Danfoss BOCK FK20 Operating Manual

5| Commissioning

5.6.1 Notes on replacing the shaft seal

Since changing the shaft seal involves encroaching into the refrigerant circuit, this is only recom-
mended, if the seal is losing refrigerant, or if oil is escaping in excess of the permissible amount (see
information on page 14, chapter 5.6, "Shaft seal"). Changing the shaft seal is described in the relevant
spare part kit.
The shaft seal is a wearing part, and its service life depends on the prevailing conditions.
Damaging effects on the shaft seal:
• Too little suction gas superheat, particularly during wet operation
• Too high or too low belt tension
• Thermal overload (operation outside the limits of application)
• Frequent cycling
• Long periods of stoppage
• Material deposits / dirt from the system
Due to these effects, the shaft seal can develop leaks, and it must then be replaced.
5.7 Avoiding liquid shocks
ATTENTION! Slugging can damage the compressor and cause refrigerant to
To prevent liquid shocks:
The complete refrigeration plant must be correctly designed and executed.
The capacities of all components must be compatible (particularly evaporator
and expansion valve).
Suction gas superheating at the evaporator output should be at least 7 – 10 K (check setting
of the expansion valve).
The system must reach a state of equilibrium.
Particularly in critical systems (e.g. several evaporator points), suitable measures, e.g.
use of liquid traps, solenoid valve in the liquid line, etc. are recommended.
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