Suction line accumulators are installed between the evaporator and the compressor. They hold liquid refrigerant so the compressor does not ingest liquid and only vapour is sent on. A U-tube and tube-in-tube design is used for maximum refrigerant flow and minimum oil hold-up: vapour is drawn from the top while oil and liquid collected in the vessel return through a hole in the return tube with the gas. Heat-exchanger accumulators are used when evaporation temperature is very low. They are recommended for parallel compressors, transport refrigeration, two-stage systems, hot-gas defrost, container cooling, long lines, reverse cycle, heat pumps and flooded evaporators. Hold-up capacity should not be below 50% of system charge; 50–70% is advised. A GVN SLA example is 33 bar maximum working pressure, 1.7 L, Ø114 mm, ODS 1/2 in, HCFC, HFC, R290 and R717, PED CAT.I/CAT.II, -20°C to +130°C.