Abstract text

A valve assembly (10), a seal assembly, an indexing arrangement, a downhole/circulation tool (12) incorporating a valve seat assembly, methods of controlling fluid flow and fluid circulation are described, wherein the valve assembly is used for controlling fluid flow by bringing a valve member (34) into sealing abutment with a deformable body (36) of the valve seat assembly, wherein at least one locking element in the form of a dog or key (38) mounted for movement relative to the body selectively between a retracted position, shown in FIGS. 1 and 2, and an extended position, shown in FIG. 7 permits a good seal between the valve member and the valve body whilst ensuring that the valve member will not be prematurely or inadvertently blown through a bore (40) in the valve body, due, for example, to variations in well conditions such as temperature and pressure.