AG 31-011 • REFRIGERANT PIPING DESIGN 14 www.DaikinApplied.com
Discharge Line Piping Details
Discharge lines carry both refrigerant vapor and oil. Since
refrigerant may condense during the OFF cycle, the piping
should be designed to avoid liquid refrigerant and oil from
flowing back into the compressor. Traps can be added to the
bottom of risers to catch oil and condensed refrigerant during
OFF cycles, before it flows backward into the compressor.
Intermediate traps in the risers are unnecessary in a properly
sized riser as they increase the pressure drop. Discharge lines
should be pitched 1/8 inch per foot (10.4 mm/m) in the direction
of refrigerant flow towards the condenser (
).
Whenever a condenser is located above the compressor,
an inverted trap or check valve should be installed at the
condenser inlet to prevent liquid refrigerant from flowing
backwards into the compressor during OFF cycles. In some
cases (i.e. with reciprocating compressors), a discharge muffler
is installed in the discharge line to minimize pulsations (that
cause vibration). Oil is easily trapped in a discharge muffler, so
it should be placed in the horizontal or downflow portion of the
piping, as close to the compressor as possible.
Figure 10: Discharge Line Piping Details
Slope in
direction of
refrigerant flow
Keep trap at
bottom of riser
as small
as possible