Overspeed safety device

An overspeed safety device for a pneumatic rotation motor, comprising a housing (10, 18) and a valve element (28) guidingly supported in a bore (27) in the housing (10, 18) and arranged to block at least the main part of the air supply to the motor when shifted from a normally open position to a closed position, an activating means coupled to a rotating part (14) of the motor and arranged to be shifted from a normal rest position to an active position at a predetermined motor speed level, and a trip means (29, 31) supporting said valve element (28) in said open position and arranged to be triggered by said activating means (37, 38) to thereby release said valve element (28) for movement toward said closed position,

• wherein said trip means (29, 31) comprises:
• an open spring wire lock ring (29) pretensioned toward a closed condition and located in a groove (30) in said valve element (28),
• a shoulder (32) in said bore (23) having an inner diameter that is larger than the outer diameter of said lock ring (29) as said lock ring (29) occupies its closed condition, and
• a holding means (31) normally located between ends of said lock ring (29) so as to maintain said lock ring (29) in an expanded condition in which an outer diameter of said lock ring (29) exceeds an inner diameter of said shoulder (32), thereby supporting the valve element (28) in said open position.