Abstract: An extremely accurate and reliable fluid pressure sensor for monitoring process pressure and sensing when predetermined pressure set points or limits have been reached. A Bourdon tube with a pivotally moving lever end responds to the process pressure. When the process pressure is within the desired pressure range, a fluid operated block and bleed relay is operated to provide a first pressure level at its outlet. As the preset pressure point is reached, the relay is operated to provide a change in the outlet pressure level for actuating suitable safety units. A pivoting beam responds to pivoting movement of the Bourdon tube lever arm about the pressure set points and effectively amplifiers or increases such movement to rapidly operate the relay. Snap-acting cap means with a self-aligning disc cap a nozzle port in the relay in response to pivoting beam movement.