an annular ridge 44 on the bonnet 34 and an annular ridge 46 on the valve body 26 clamp the outer periphery of the diaphragm 10 to form a seal between the outer periphery of the diaphragm 10 and the valve body 26 the coating 22 on the periphery of the diaphragm 10 acts as a seal between the diaphragm flexible metallic member 20 or substrate and the valve body 26 in the example illustrated by fig1 2 a and 2 b the actuator 13 is assembled to the valve assembly 12 by the bonnet nut 36 the illustrated bonnet nut 36 includes internal threads 56 that engage external threads 58 of the actuator 13 the actuator 13 selectively extends an actuator rod 60 to move a button 62 along a path of travel defined by the bonnet 34 when the rod 60 is extended the button 62 deflects the diaphragm 10 into sealing engagement with the valve seat 18 when the rod 60 is retracted the diaphragm 10 flexes away from the valve seat 18 to open the flowpath between the inlet port 14 and outlet port 16 fig4 a schematically illustrates where the bonnet annular ridge 44 engages the diaphragm 10 when the valve arrangement 12 is assembled phantom line 50 illustrates the contact location of the bonnet annular ridge 44 on the actuator side 28 of the diaphragm 10 the bonnet annular ridge 44 may contact the diaphragm 10 along the phantom line 50 or may contact an area of the diaphragm 10 such as for example the area on the diaphragm.