The cold head and its operating principle

Within the cold head, a cylinder is divided into two working spaces and Vj by a displacer. During operation the right space is warm and the left space Vj is cold. At a displacer frequency f the refrigerating power W of the refrigerator is  

The displacer is moved to and fro pneumatically so that the gas is forced through the displacer and thus through the regenerator located inside the 

The series-manufactured refrigerator cryopumps from LEYBOLD use a two-stage cold head operating according to the Gifford-McMahon principle (see Fig. 2.67). In two series connected stages the temperature of the helium is reduced to about 30 K in the first stage and further to about 10 K in the 

The displacer is at the left dead center Vj where the cold is produced has its minimum size. Valve N remains closed, H is opened. Gas at the pressure p flow/s through the regenerator into Vj. There the gas viarms up by the pressure increase in VI. 

With valve N open the displacer moves to the left the gas from Vj flows through the regenerator, cooling it down and then flows into the volume V and into the low pressure reservoir. This completes the cycle. 

---