Downhole assemblies and methods for isolating a wellbore. A downhole tool can include a body having a bore or flowpath formed therethrough, and one or more sealing members disposed therein. The one or more sealing members can include an annular base and a curved surface having an upper face and a lower face, wherein one or more first radii define the upper face, and one or more second radii define the lower face, and wherein, at any point on the curved surface, the first radius is greater than the second radius. The sealing members can be disposed within the bore of the tool using one or more annular sealing devices disposed about the one or more sealing members.

An inlet support structure for use with a rupture disc, the inlet support structure including an annular member having an inner diameter, an outer diameter, a plurality of spaced apart cut-outs extending from the inner diameter towards the outer diameter, a central non-circular opening extending through the annular member and including the cut-outs, the cut-outs providing additional space for the petals of a rupture disc to be received therein when the rupture disc ruptures so as to provide a greater flow area through the rupture disc.

An inlet support structure for use with a rupture disc, the inlet support structure including an annular member having an inner diameter, an outer diameter, a plurality of spaced apart cut-outs extending from the inner diameter towards the outer diameter, a central non-circular opening extending through the annular member and including the cut-outs, the cut-outs providing additional space for the petals of a rupture disc to be received therein when the rupture disc ruptures so as to provide a greater flow area through the rupture disc.

Downhole assemblies and methods for isolating a wellbore. A downhole tool can include a body having a bore or flowpath formed therethrough, and one or more sealing members disposed therein. The one or more sealing members can include an annular base and a curved surface having an upper face and a lower face, wherein one or more first radii define the upper face, and one or more second radii define the lower face, and wherein, at any point on the curved surface, the first radius is greater than the second radius. The sealing members can be disposed within the bore of the tool using one or more annular sealing devices disposed about the one or more sealing members.

A control regulator includes a diaphragm assembly with an integrated pressure relief mechanism. The diaphragm assembly includes a diaphragm with a locally weakened area and a diaphragm plate with an opening aligned with the locally weakened area.