A fuel vapor storage canister is provided. The canister includes a vapor storage chamber of variable volume, a partition, vapor adsorbing material, and a volume compensator. The partition is movable within the canister and partially defines the vapor storage chamber. The vapor adsorbing material is located in the vapor storage chamber. The volume compensator includes a spring having at least three legs that are deflected by and exert pressure against the movable partition to control the volume of the vapor storage chamber. In one embodiment, the legs of the spring may be evenly spaced to exert a balanced pressure. The spring may include two pairs of opposing legs, where the spring rate between the pairs of legs may vary. The spring may be comprised of two angularly offset band springs and may be formed from a unitary member.