Backhead and drill assembly with backhead

A portion of a drill assembly operated by a supply of compressed fluid, comprising:

• a backhead having a proximal end connectible to the supply, an axial bore and an open distal end having defined therein an integrated cylinder portion, the backhead having passages extending between the axial bore and outer surface of the backhead;
• a cylinder portion aligned with and in selective fluid communication with the backhead;
• a hollow elongate wear sleeve surrounding the cylinder portion and connected to the backhead;
• a piston housed by the wear sleeve and having a proximal end shaped to fit within the cylinder portion, the piston being slidably movable along the wear sleeve and the cylinder portion in response to compressed fluid conveyed through the backhead;
• wherein when the drill assembly is in a drop open position, the proximal end of the piston is spaced apart from the cylinder portion and the wear sleeve.