Emerson Copeland Scroll Introduction Manual page 40

4.4 Oil equalization line
The oil equalization line between the two or three compressors must be at least 7/8" (22 mm) with a minimum inner diameter of 19
mm. On no account must the internal diameter of any fitting in this line be less than 19 mm. It is strongly recommended that a sight
glass be fitted using adaptors. Kits consisting of the adaptor shown below, plus conversion to brazed connections are available (see
spare parts lists for details). The equalization tube must be level, and the compressors must be mounted level. Tests have shown that
smaller tube diameters do not provide proper oil balancing. An oil separator may be used and the oil return line from the separator
should be connected to the oil equalization line.
If no oil separator is installed the oil returns into the suction header and is picked up there from the individual compressor suction lines.
1 1/4" – 12 UNF 3/4" – 14 NPTF
7/8"
Figure 4: Adaptor for oil sight glass connection
NOTE: Tightening torque: 41-54 Nm. Use Loctite string or Everseal 483 White Pipe Sealant.
4.5 Oil and gas equalization plus oil regulator
If the OMB or other device is fitted to the equalization line, one device serving 2 or 3 compressors, the proper functioning of
the system has to be checked to ensure that no nuisance tripping occurs. The OMB sight glass, remote from the sump, does not
always accurately follow the sump oil level. The oil separator must be of the combined separator/reservoir high-pressure type, or
alternatively a separate oil reservoir may be used if the separator has its own float valve. The separator float valve outlet must not be
connected directly to the OMB.
5. Oil return to running compressors
If oil returns to the compressor at approximately the same rate as it leaves then the oil level will be maintained. It is always preferable
to design the suction manifold in such a way that oil returning with the suction gas can only enter the running compressor(s). This
can be done in a number of ways. Perhaps the most common is to use a suction header with vertical pick-ups to each compressor
which induces sufficient velocity to lift the oil. Again certain designs have been shown to be satisfactory but each one has to be
proven by testing. With some system designs this is sufficient to ensure adequate oil level at all times but there is no fail-safe
pressure switch if one compressor loses oil.
Recommended Not recommended
From evaporator(s)
From evaporator(s)
From evaporator(s)
Suction lines to compressors
Figure 5: Suction header/lines to compressors – Recommendation
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