US Patent 9464510 Trigger mechanism

A trigger mechanism for a ball activated device comprises a seat sleeve with seat defining members forming a fluid seal between the ball and the seat in an initial state and allowing the ball to pass through the seat in a final state. An alternating member can move radially in an aperture through an inner sleeve and abuts an outer surface on the seat sleeve in the initial state, is received in a recess on the seat sleeve in an intermediate state, and is received in a groove in the outer sleeve in the final state. A protective sleeve may extend axially from the seat sleeve over a seat receiving area. The mechanism is suitable for cementing and fracturing as particles cannot penetrate to its moving parts.