like those designed for pleasure boat ice box conversions have to deal with design and application concepts that are all different. Because there are no two boat installations the same pressure drop and velocity changes do occur. Compressor
manufacturers establish high and low pressure refrigeration
tubing size required by size of line connectors on their compressors. Small pressure drops throughout a refrigeration system, line flow frictions, turns, line connecters and tubing bend losses are normally controlled within reason by the refrigerant flow control device.
When 134a refrigerant is used in a boat refrigerator
the low side pressure is rarely higher than 10 psi. If your installation
has all devices sized to compressor
flow line sizes, flow velocity will be your concern and not pressure drop. The compressor depends on flow velocity to return lubricating oil
and to cool compressor.