the type of the measuring device 6 is conveyed to the back side where the contact line 61 runs into a link 62 the measuring device 6 as well as the contact line 61 is preferably applied in thin film technology on the flattening 24 of the basic body 2 as measuring device 6 preferably an elastic measuring strip 60 is used however also other concepts are known and can be used for that purpose in a first modification of the invention it is provided that the membrane 4 with its front end facing the pressure space 3 acts directly on the seal 5 in another alternative improved embodiment the membrane 4 is linked at its front end facing the pressure space 3 to a support edge 21 which stabilises the membrane mechanically respectively supports the cylinder wall 36 additionally by means of this support edge 21 an improved sealing between the membrane and the pressure space 3 is generated as a considerably larger seal surface is provided for interacting with the seal 5 at the support edge if this is designed for example in three segments according to the invention however both variants are possible that means the arrangement with or without supporting edge 21 the invention shown in fig1 is characterised in.