A gas separation valve assembly for a diesel motor system having a tank with a float therein controlling a valve mechanism through which fuel is dispensed from the tank. A dual sleeve assembly is arranged within the tank having an inner sleeve with a lower end in fluid-tight connection with the tank and an outer sleeve arranged to define an annular space between itself and the outer wall of the tank and an intermediate space between itself and the inner sleeve. Fuel is introduced into the tank through an aperture so as to flow into the annular space between the tank wall and the outer sleeve and then to pass through the intermediate space so as to overflow the inner wall and to flow into an interior space of the tank within which the float is located.