How SPGs are made?

As divers, we often make important decisions based on the cylinder pressures indicated by these very simple mechanical devices. But have you ever wondered how it’s made and what goes on inside them?

A typical SPG has an all brass chrome plated housing with a tempered mineral glass face and features a beryllium copper coiled Bourdon tube mechanism. The rack and pinion movement (aka ‘pinned’) provides the greatest degree of accuracy and reliability. The Bourdon tube bend slightly as the SPG is pressurized and as the tube flexes, the indicator needle rotates around the dial in relationship to the movement of the tube.