Extensible piston with breakable or displaceable coupler

Abstract From the Canadian patent

A fluid pressure actuated piston (78) is slidably carried in a fluid pressure actuated cylinder (50) which in turn, is slidably carried in a fixed carrier or casing (21). Movement of the cylinder (50) is resisted by a breakable or displaceable coupler (90, 94 184, 185) which, engages the cylinder (50). Fluid pressure acting upon the cylinder (50) and piston (78) causes the coupler (90 94, 184, 185) to break or be displaced and release the cylinder (50) for axial movement in the direction of movement of the pressure responsive piston (78).