Coupling with pressure relief

A coupling for a break-away valve assembly, said coupling comprising:

• an annular body, the annular body having a first end, a second end, a valve seat comprising a first portion and a second portion, the second portion being adjacent to the first portion and having an internal diameter larger than an internal diameter of the first portion,
• a main flow valve arranged in the annular body, the main flow valve being biased in a first direction toward the first end to seal against the valve seat on disconnection of the coupling from an adapter,
• wherein the main flow valve is biased in a second direction toward the second end,
• wherein the main flow valve is adapted to extend past the first portion into the second portion of the valve seat to release a volume of fluid if the pressure acting on the main flow valve exceeds a predetermined surge pressure threshold,
• wherein the main flow valve has a valve head, a perimeter of the valve head having a sealing surface, and
• wherein the sealing surface of the valve head contacts the first portion of the valve seat in a first position and moves in the first direction to a second position in the second portion of the valve seat to release the volume of fluid, the sealing surface of the valve head spaced from the second portion of the valve seat in the second position.