Ball seat assembly and method of controlling fluid flow through a hollow body

A method of controlling fluid flow through a hollow body, the method comprising the steps of:

• mounting a ball seat within a bore of the body;
• locating the ball seat in an extended position in which the ball seat defines a restriction to passage of a ball along the body bore;
• bringing a ball into abutment with the ball seat, to restrict fluid flow through the body bore and thereby causing an increase in a fluid pressure force acting on the ball seat for a given fluid pressure;
• and
• subsequently lowering the fluid pressure force acting on the ball seat, to facilitate movement of the ball seat from the extended position to a retracted position spaced axially along the body bore from the extended position, in which position the ball seat releases the ball and permits passage of the ball along the body bore to thereby re-open fluid flow along the body bore.

A ball seat assembly comprising:

• a hollow body defining a body bore;
• a ball (20) adapted to be passed down into the body bore in a first axial direction;
• and
• a ball seat mounted within the body bore, the ball seat adapted to receive the ball and being selectively movable relative to the body bore in a second axial direction opposite to said first axial direction between an extended position in which the ball seat defines a restriction to passage of the ball along the body bore, and a retracted position in which passage of the ball along the body bore is permitted.