passes through a filter dryer 21 to remove moisture and small dust particles and then through a refrigerant expansion device or pressure reducing device 22 where the refrigerant normally starts changing from the liquid to the gaseous phase within the evaporator 12 reference character 23 illustrates a ball valve or shut off valve used for purposes of pump down or isolation of parts of the system after the refrigerant enters the evaporator 12 where it is boiled off at low temperatures the refrigerant vapor is drawn back to the compressor 10 via line 24 from the top of the evaporator through an accumulator 25 to be re compressed by the compressor thus completing the cycle it should be pointed out that although only one set of components is shown it will be appreciated that one or more compressors can be used with the system as well as one or more of all the other components since most refrigerant hydrocarbons such as freon 22 are completely miscible or compatible with the oils used to lubricate the compressor it is frequently desirable to provide a bleed line to continuously separate the oil from the refrigerant and as well as line 18a illustrated a further line 18b is shown extending from the evaporator to the compressor not shown are pressure gauges or thermometer indicators which are usually installed for purposes of uniform operation although they are not essential to the operation of the system the above explanation covers the refrigeration cycle which is basically similar to all other refrigeration equipment however the evaporator 12 which is approximately half full of low temperature liquid freon 22 acts as a container whereby a liquid pump 26 pumps liquid refrigerant from the.