A slam-shut safety valve for a gas distribution system the slam-shut safety valve comprising: a valve body; a diaphragm disposed at least partially within an interior portion of the valve body, with at least part of the diaphragm being displaceable into the interior portion of the valve body, the diaphragm having a first side being exposed to gas system pressure; a cam assembly comprising a cam and a torsional spring, the cam having an elongated first cam arm, a planar first side surface, and an opposite planar second side surface parallel to the first side surface, and being pivotable about a rotational axis disposed adjacent to a first end of the first cam arm; a plunger connected to the first side of the diaphragm and to the first cam arm; and a reset pin assembly, the reset pin assembly including an elongated reset rod and a relatch plug fixedly coupled to the reset rod; wherein the cam is rotatably mounted within the interior of the valve body; the cam includes an elongated cam body that extends longitudinally along a cam body axis that intersects the rotational axis and has a top portion and a bottom portion opposite the top portion; the first cam arm extends from the bottom portion of the cam body along a first cam axis that bisects the first cam arm and intersects the cam body axis at an acute angle; a second cam arm extends from the top portion of the cam body in a direction opposite and parallel to the first cam axis of the first cam arm; the cam has a third cam arm; the torsional spring is operatively coupled to at least one surface disposed in the interior portion of the valve body and comprises a pair of stationary outer arms (20a, 20b), a first pivotable inner arm positioned adjacent the first side surface of the cam, and a second pivotable inner arm connected to the first pivotable inner arm through a cross arm that extends from a distal end of the first inner arm to a distal end of the second inner arm and positioned adjacent the second side surface of the cam; the first pivotable inner arm and the second pivotable inner arm prevent the cam from laterally displacing, are coupled to a portion of the first cam arm through engagement of the cross arm with a shoulder of the first cam arm that is adjacent to a distal end of the first cam arm, and are adapted to act on the first cam arm to bias the cam into a position that allows the cam to be relatched in a valve rearming process; and the torsional spring is adapted to act on the first cam arm to bias the cam into a desired position that allows the third cam arm to engage a shoulder portion of the relatch plug when the reset rod is displaced towards the cam in a valve rearming process, thereby relatching the cam. a valve body; a diaphragm disposed at least partially within an interior portion of the valve body, with at least part of the diaphragm being displaceable into the interior portion of the valve body, the diaphragm having a first side being exposed to gas system pressure; a cam assembly comprising a cam and a torsional spring, the cam having an elongated first cam arm, a planar first side surface, and an opposite planar second side surface parallel to the first side surface, and being pivotable about a rotational axis disposed adjacent to a first end of the first cam arm; a plunger connected to the first side of the diaphragm and to the first cam arm; and a reset pin assembly, the reset pin assembly including an elongated reset rod and a relatch plug fixedly coupled to the reset rod; wherein the cam is rotatably mounted within the interior of the valve body; the cam includes an elongated cam body that extends longitudinally along a cam body axis that intersects the rotational axis and has a top portion and a bottom portion opposite the top portion; the first cam arm extends from the bottom portion of the cam body along a first cam axis that bisects the first cam arm and intersects the cam body axis at an acute angle; a second cam arm extends from the top portion of the cam body in a direction opposite and parallel to the first cam axis of the first cam arm; the cam has a third cam arm; the torsional spring is operatively coupled to at least one surface disposed in the interior portion of the valve body and comprises a pair of stationary outer arms (20a, 20b), a first pivotable inner arm positioned adjacent the first side surface of the cam, and a second pivotable inner arm connected to the first pivotable inner arm through a cross arm that extends from a distal end of the first inner arm to a distal end of the second inner arm and positioned adjacent the second side surface of the cam; the first pivotable inner arm and the second pivotable inner arm prevent the cam from laterally displacing, are coupled to a portion of the first cam arm through engagement of the cross arm with a shoulder of the first cam arm that is adjacent to a distal end of the first cam arm, and are adapted to act on the first cam arm to bias the cam into a position that allows the cam to be relatched in a valve rearming process; and the torsional spring is adapted to act on the first cam arm to bias the cam into a desired position that allows the third cam arm to engage a shoulder portion of the relatch plug when the reset rod is displaced towards the cam in a valve rearming process, thereby relatching the cam.