Non-return check valve and check valve apparatus for vacuum system

A vacuum system non-return valve comprising:

• a baffle for extending across a flow path in said vacuum system, said baffle comprising an aperture, a perimeter of said aperture comprising a valve seat;
• a valve member comprising a curved sealing surface configured to mate with said valve seat, said valve member and aperture being configured such that said valve member obscures said aperture and seals with said valve seat to impede a flow of fluid from an outlet end to an inlet end in a closed position and is displaceable in use to move away from said valve seat and allow a fluid flow from said inlet end to said outlet end in an open position;
• at least a portion of a surface of said baffle surrounding said aperture slopes inwardly towards said inlet end of said valve such that said aperture is smaller at said inlet end than it is at said outlet end;
• wherein
• diametrically opposing portions of said sloped surfaces of said aperture subtend an angle of between 30° and 70°;
• and
• wherein the angle of the sloped surface and the relative sizes of the aperture and valve member are selected so that the sloped surface at the valve seat is tangential to the curved sealing surface of the valve member.