the annular flange 48 of the bellows 46 and the valve plate 50 and is connected to these parts in each case in a gas tight manner by welding adhesive bonding or screwing in the drawing for the sake of clarity in each case only the snap disk determining the function is shown in practice it may be expedient to use in each case a plurality of identical snap disks fitted in the same direction the function of the valve arrangement 24 is described below with reference to fig4 to 13 the position of the snap disks which is shown in fig4 and 5 is maintained during heating up to 115 u00b0 at 115 u00b0 c the snap disks 94 and 94 a switch over into their opposite curvature position according to fig1 the overall height and thus the position of the valve ball 90 does not change in the process when the second switch over temperature of 117 u00b0 c is reached the snap disks 96 and 96 a additionally switch over into their opposite curvature position as can be seen from fig1 the overall height of the stack and the position of the valve ball 90 remain unchanged so that the valve ring 26 remains lifted from its valve seat 28 i e the valve remains open so that the media exchange can continue to be effected without hindrance according to the invention measures are taken in order to hold the valve in the open position even when during the sterilization operation a flow pressure loads the valve body formed by the valve plate 50 this flow pressure attempting to close the valve.