US Patent 7168492 Wellbore annulus flushing valve

The invention relates to downhole wellbore apparatus and particularly, but not exclusively, to apparatus for use in wellbore cleaning operations. A downhole tool (2) comprises a body (4) having a bore extending longitudinally therethrough, wherein the tool (2) further comprises a one-way valve (24,26) for allowing a flow of fluid in a first direction through the tool bore and preventing a flow of fluid in a second direction through the tool bore, the second direction being opposite to the first direction. The tool further comprises mandrel (38) for rendering the one-way valve (24,26) inoperable so as to be ineffective at preventing fluid flow; and a shear pin assembly (44,40) for selectively making the one-way valve operable so as to be effective at allowing fluid flow in the first direction and preventing fluid flow in the second direction.