HSO 2024 to HSO 2035 Installation, Operation and Maintenance Manual
Page 36 of 94
Publication 2-119
Issue 1.2 : 03/10
6.4.1.
Oil Return
As already mentioned in 6.2, the separator must be positioned at a
suitable height such that the standing oil level (compressor stopped) is
significantly below the bottom of the compressor. For applications using
a continuously running oil pump a drain line must be installed between
the compressor casing and the oil separator.
The oil separator must have a sufficient free volume to accommodate the
oil drainage from the compressor or oil returned from another part of the
system.
6.4.2.
Suction/Discharge Non-return Valve
To prevent excessive reverse rotation of the compressor at shutdown it is
necessary to fit a non-return valve adjacent to the compressor in the
suction and/or discharge lines:
•
Single compressor application - either a suction or discharge
non-return valve must be fitted. A non-return valve in the
suction line must be located before the suction strainer.
•
Multiple compressor application - all compressors must be
fitted with a discharge non-return valve.
NOTE: discharge non-return valves must be sized
according to the operating conditions.
6.4.3.
Oil Heaters
The separator must be fitted with oil heaters of sufficient capacity to
maintain an oil temperature 20
°
C above the ambient temperature,
thereby preventing refrigerant migration into the oil and the resultant loss
of viscosity and potential foaming. The oil heaters must be electrically
interlocked to energise when the compressor stops.
If the plant is sited in a cold environment then oil lines must be suitably
lagged and if necessary heater tape applied in order to prevent oil
foaming.
6.4.4.
Oil Low Level
A level switch or sensor must be fitted to the oil separator or the main oil
line at a point corresponding to a dangerously low oil level. The switch or
sensor must be electrically interlocked to prevent the compressor starting
unless there is sufficient oil in the reservoir, and stop the compressor
should the oil level fall below the danger level.
6.4.5.
Oil Balance Lines
In installations using multiple compressors/oil separator units on the
same refrigeration circuit, oil returning from the system must be
distributed such that an adequate oil level is maintained in each oil
separator. If an oil balance system is adopted that relies on solenoid
valves to prevent oil returning to the separator when the compressor is
stopped, these solenoid valves must be selected and tested as suitable
for use with refrigeration oils. Many such valves fail to close, with the
possibility of oil flowing through the non running oil system/compressor
and filling the compressor. This can occur even when a non return valve
is fitted after the separator.
