Cryogenic refrigerators

Abstract

The present invention provides a coldhead drive unit for a cryogenic refrigerator including a casing having an inlet for supplying a fluid into the casing at a working pressure and a valve positioned within the casing for controlling the supply of the fluid to and from the cold head. The valve comprises a valve plate and a valve head positioned against the valve plate and having a surface distal to the valve plate against which the working pressure acts. An effective pressure of less pressure than the working pressure acts at the interface between the valve head and the valve plate so that an axial force is exerted upon the distal surface of the valve head, driving the valve head against the valve plate. Additionally, a motor is included having a drive shaft for rotating the valve head against the valve plate. The drive shaft engages the valve head in a fluid tight manner within a bore formed in the distal surface of the valve head and the valve head has a channel linking the sealed interior of the bore and the interface between the valve head and the valve plate. As a result, the area of the distal surface subjected to the working pressure is reduced in an amount equal to the cross-sectional area of the bore to thereby reduce the magnitude of the axial force.

Dependencies are inferred from the claim text.