A check valve (20) with a body (22) and a hole (30) extending from an inlet (24) to an outlet (26). A piston assembly (52), mounted in the body (22), includes a piston (54), a check valve seal (60) and a piston spring (55). The piston spring (55) biases the piston (54) to a first location preventing air from flowing from the inlet end (24) toward the outlet end (26). The check valve seal (60) is positioned to seal against a check valve seat (37). Movement of the piston (54) removes the check valve seal (60) from the check valve seat (37), allowing air to flow from the inlet end (24) toward the outlet end (26). A tapered portion (64) of the hole (30) permits usage with systems having different volume output levels. A dampener (31) reduces fluctuations of the piston (54) caused by cyclical fluctuations in fluids controlled.