Abstract: There is disclosed a flow control mechanism for a downhole tool and a downhole tool incorporating the flow control mechanism. In one embodiment, a flow control mechanism (202) is disclosed for controlling a centralizer (200). The flow control mechanism (202) comprises a body (212) defining a fluid chamber (234); an inlet flow path (292) for fluid flow into the chamber (234); at least one tool flow path (294) for fluid flow between the chamber (234) and at least part of the downhole tool (200); an exhaust flow path (297) for fluid flow from the chamber (234) to a fluid exhaust (240); and control means including a control member (218) mounted for movement within the chamber (234) for controlling flow into and out of the chamber (234) along the inlet flow path (292), the at least one tool flow path (294), and the exhaust flow path (297). The mechanism (202) controls flow to a piston (214) of the centralizer (200) for centralizing the centralizer (200) within, for example, a tubular (211) in the bore hole.