What is the difference between a standard pressure gauge and a safety pattern version?
A safety version (code S3 per EN837) has an additional solid baffle wall welded between the dial and the measuring system. In addition, the case has a back wall that can blow out completely. The window is typically made of laminated safety glass. If a pressure builds up in the housing (e.g. from a rupture in the Bourdon tube), this pressure will exhaust completely through the back wall, which is then ejected from the case by the pressure. A release of pressure through the window cannot occur, so there is no risk to personnel through splinters of flying glass. At WIKA these instruments are specially marked on the dial with an "S" in the circle.