Large commercial or industrial refrigeration systems may have multiple expansion valves and multiple evaporators in order to refrigerate multiple enclosed spaces or rooms. In such systems, the condensed liquid refrigerant may be routed into a pressure vessel, called a receiver, from which liquid refrigerant is withdrawn and routed through multiple pipelines to the multiple expansion valves and evaporators. Filter Dryers, installed before the compressors to catch any moisture or contaminants in the system and thus protect the compressors from internal damage Some refrigeration units may have multiple stages which requires the use of multiple compressors in various arrangements.[4]