Overpressure switch with ball valve contact

Abstract From the Canadian patent

An electrical pressure switch that can be readily adapted for either normally open or normally closed operation and that has opposed annular seats, a movable contact and ball valve movable between and individually engageable with the seats and an O-ring uniquely associated, with the ball valve and a related sealing surface in seated unseated and, all intermediate positions of the valve to maintain an effective seal at all times against fluid pressure to which the switch is connected.