Abstract: A cryogenic apparatus cools an object to, and maintains it at, very low terature and is of the kind in which a refrigerating medium comprising superfluid helium II is evaporated from a supply container into an evacuable exhaust system through a throttle element. Such element includes a valve comprising a valve element displaceable relative to a valve sleeve, and the element and sleeve define a passage gap which, in the normal control range, has a width of less than 10 .mu.m and a length determined by the position of the element relative to the sleeve. Such valve may have an additional control range in which the width of the passage gap is greater than 10 .mu.m. The valve element may be a cylindrical plunger which is axially movable within the sleeve and which defines with the sleeve over at least part of its movement an annular gap having a width less than 10 .mu.m.