Overspeed safety device for a rotation motor

Overspeed safety device for a pneumatic rotation motor including a cylinder (10), a pressure air inlet opening (21), and a rotor (13), comprising an actuator (18) co-rotating with the rotor (13) and responsive to centrifugal action, and a valve element (20) arranged to control the air flow through the inlet opening (21), said valve element (20) is arranged to be engaged by the actuator (18) for initiating a shifting movement of the valve element (20) from an open position to closed position as the rotor speed exceeds a predetermined maximum speed level, said valve element (20) is formed by a lid which is tiltable about a pivot axis (C) between the open position and the closed position, and said pivot axis (C) extends substantially along a chord related to the centre of the rotor (13), and the actuator (18) is formed with a cam surface (25) for caming engagement with said lid (20) for accomplishing tilting of said lid (20) about said pivot axis (C), wherein

• said inlet opening (21) is surrounded by a flat seat surface (32) for sealing engagement by the lid (20) in the closed position of the latter,
• said lid (20) is formed with at least one ridge portion (33,34) for resting on said seat surface (32),
• a spring (26) is arranged to retain and bias said lid (20) toward said seat surface (32) such that when shifted between the open position and the closed position the lid (20) is made to perform a bi-stable over-centre movement by the ridge portion or portions.