Diaphragm seals are used to protect the pressure measuring instrument from aggressive, adhesive, crystallising, corrosive, highly viscous, environmentally hazardous or toxic media. A diaphragm made of the appropriate material provides for the separation from the medium to be measured. Thus even the most difficult measuring requirements can be met by combining measuring instruments with diaphragm seals. A fluid inside the system, which can be chosen to suit the particular application, hydraulically transmits the pressure to the measuring instrument. The diaphragm, welded for model without intermediate ring and mechanically clamped between the upper housing and intermediate ring for model with intermediate ring, is leak proof tested to guarantee fill fluid separation from process fluid. This diaphragm seal can be cleaned by removing the lower housing. This construction feature and its compact design suits to many applications requiring frequent maintenance.