Evaporator and expansion valve

The explanations here apply to most screw compressors and most refrigerants. For OS.A compressors with R717 (ammonia):

The expansion valve and evaporator must be coordinated with the greatest care, especially in systems with a large control range (e.g. capacities of 50 to 100% or 25 to 100%, cf. ST-430). Sufficient suction gas superheat and stable operation must be assured at both full load and part load. After switching from part to full load, there is a risk of liquid slugging. Therefore, the evaporator and expansion valve must be dimensioned in such a way that oil is not separated in the evaporator even at part load.

Depending on the design and capacity range of the evaporator, it may therefore be necessary to divide it into several refrigerating circuits (Systems with multi-circuit condensers and/or evaporators).

If electronic expansion valves with a shut-off function are used, the control must be programmed so that the valve closes tightly immediately after the compressor is shut off or, for example, in the event of a power failure.