Back pressure valve

A method comprising:

• positioning a valve seat in a first bore portion of a housing of a valve assembly;
• positioning a valve element in a second bore portion of the housing, the second bore portion having a larger radial dimension than the first bore portion, wherein the first and second bore portions are radially offset;
• and
• linearly actuating the valve element from a closed position in which the valve element blocks fluid flow through the housing in at least one direction to an open position in which the valve element is spaced axially apart from the valve seat.

A downhole valve, comprising:

• a top sub comprising an upper connection for connecting to a superposed tubular of a workstring;
• a first valve assembly coupled to the top sub;
• a second valve assembly coupled to the first valve assembly;
• and
• a bottom sub coupled to the second valve assembly and comprising a lower connection for connecting to a subjacent tubular of the workstring,
• wherein:
• the top sub, first valve, second valve assembly, and the bottom sub cooperatively define at least a portion of a bore extending axially therethrough, and
• the first valve assembly comprises:
• a housing coupled to the top sub and the spacer sub;
• and
• a module including a valve seat and a valve element, the module being non-concentrically disposed within the housing, such that a centerline defined through the valve seat and the valve element is offset from a central axis of the housing,
• wherein the valve element is linearly actuatable between a closed position in which the valve element engages the valve seat and blocks the bore and an open position in which the valve element permits flow of fluid therethrough.