Nested flapper spring

A device in accordance to an embodiment includes a tubular housing having an inside diameter defining an axial bore, a top surface and an outer surface, a groove formed along the outer surface below the top surface, a flapper pivotally connected with the housing and pivotal between an open position to allow flow through the bore and a closed position to block flow through the bore and a torsion spring having a spring diameter and disposed in the groove and in connection with the flapper to bias the flapper to one of the open and the closed position. The torsion spring may be nested in a C-shaped groove.