A valve (1) comprises a spring arrangement comprising a stiff (5) and a weak spring (6). The weak spring (6) has the form of a thin, circular disc having a first spring surface (6′) and a second spring surface (6′), and an inner spring part (6a) and an outer spring part (6b) substantially separated from each other with cavities (6c), yet at two points, at least, connected with legs (6d). The effect of the connection is that the outer spring part (6b) and the inner spring part (6a) can deflect in relation to each other.